Physical quantities
Physical quantity is a Physical property that can be measured. Eg: length,time, mass, velocity,
force,
Physical quantity
S.I Base unit
Symbol
Length
meter
m
Mass
kilogram
kg
Time
second
s
Scalar quantity
A quantity which has only magnitude and no direction. Eg:distance,speed, pressure,kinetic
energy,work
Vector quantity
A quantity which has both magnitude and direction. Eg: Displacement, Velocity, moment,
torque, momentum, weight, force, acceleration
Distance
The distance travelled by an object is the total length that is traveled by that object.
SI unit: meter (m)
Quantity: Scalar
Displacement
Displacement is the distance travelled in a particular direction. Or The shortest distance from
the initial point to the final point.
SI unit: meter (m)
Quantity: vector
School
Home
Speed
speed =
m
dis tan ce (travelled)
 m/s
=
time*(taken)
s
-
Scalar quantity
Speed is the distance travelled per second
1
Displacement
“rate” means divided by time. rate =
1
time
So the rate of change of distance is called speed.
Eg : You are running at 10ms-1. This means that every second you are running 10 m.
Average speed =
total dis tan ce travelled
total time taken
Velocity
Velocity =
displacement m
  m/s
time
s
Vector quantity
Rate of change of displacement is called velocity.
Change in velocity = final velocity – Initial velocity
= v  v  u
Acceleration -Acceleration =
“” means “change in”
rate of change of velocity
change in velocity / ( gain in velocity)
time taken
=
v v  u

a
t
t
m/s
 m / s2
s
-
Vector quantity
If
velocity is constant
acceleration is zero
Deceleration ( retardation )
Deceleration =
loss in velocity m / s

 m / s2
time taken
s
Negative acceleration is known as
deceleration
Deceleration = - acceleration
2
Q1) An aeroplane flies a distance of 1150 km from London to Oslo in 1 hour and 30 minutes.
The return journey follows a different flight path and covers a distance of 1300 km in 2
hours. Calculate:
1. the average speed of the aircraft
2. its average velocity over the two trips.
Q2) Calculate the average speed in ms- of
I)
a sprinter who completes 100 m in a time of 10 s,
ii)
a marathon runner who takes 2 ¼ hours to run 42.5 km.
Graphs
Equation of a straight line graph is y = mx + c where m Usually x – Independent variable
y=mx+C
y
y
y – Dependent variable
x
y(1
y2
x
A (x1, y1)
B
x2

x
y
y = m1 x
y
y = m2 x
1
x1
gradient = m =
y1  y 2  y

x1  x2  x
m = tan  =
y
x
2
m 1 > m 2 1 > 2
x  is less than 90

gradient is positive
 > 90 gradient
is negative
A gradient is a measure of the steepness of a line or curve ie the steepest part of a curve has
the biggest gradient.
A tangent shows the gradient on a curve at a specific instance the gradient of a curve varies.
The gradient of a curve represents the quantity that you get from dividing the y quantity by
the x quantity.
3
The area under a curve represents the quantity that you get from multiplying the y quantity
and the x quantity.
Gradient increases
3
y
y
Gradient decreases
y
2
A
1
x
x
x
y
y
y


x
x
x
Motion graphs
Distance – time graph
Rest
d Constant velocity
Gradient of a displacement - time graph =
d
Constant acceleration
Constant deceleration
 y displacment

 Velocity
x
time
Speed – time graph
Gradient of a velocity – time graph =
 y  Change in volocity

x
time
= acceleration
Area between the velocity – time graph and the time axis = y  x = displacement or distance.
4
Mass - scalar quantity
It is the amount of matter contained in a substance.Unit- kg
Inertia ---Inertia is the reluctance of a body to change its velocity.
Newton’s first law of motion
A body will remain at rest or continue to move with constant velocity in a straight line as long
as the forces on it are balanced.
Gravitational acceleration ( g )
An object falling freely under the gravitational attraction of the Earth is moving with uniform
acceleration. This acceleration is called gravitational acceleration or acceleration of free fall.
The value of gravitational acceleration is 10 ms-2.The gravitational acceleration decreases
with height and it is independent of the mass of a body.
Force
A force is a push or pull exerted by one object on another. Force is a vector quantity
Force = mass x acceleration
F = ma
unit kg ms-2 = 1 N
F – resultant force
One Newton is the force which gives a mass of 1 kg and acceleration of 1 ms 2.
Since a force is a vector quantity it can be represented by a line with an arrow on it. The
length of the line represents the magnitude of the force and the arrow shows in which
direction it is acting.
10 N force acting to the right
Scale 1 cm 2N
5 cm = 10 N
Types of force
1. Gravitational force (Weight)
weight is the gravitational force of the earth acting on a body.
weight = mass x gravitational acceleration
w =mg
unit of weight = N
weight is a vector quality
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2. Solid -solid contact forces
a. Normal Reaction forces / Normal contact force
When two solids are in contact they will push each other.
The force is normal (perpendicular) to the plane of contact
Reaction = R
Reaction = R
R = WCosθ
θ
W θ
Weight = W
b. Tangential Frictional forces
It is the force that opposes relative sliding motion between
two surfaces in contact.
R
R
F
Frictional
W
W
force
3. Thrust
Thrust
Reaction
Thrust
Frictio
Weight
Weight
4. Tension forces
When we pull a string down, an equal and opposite force called tension acts as shown
pull
Tension
T
tension
T
Weight
Forces on the string Forces on the bob pull
of string
5. Electrostatic forces (force between two changes)
Like charges repel each other
+
Unlike charges attract each other
Q1
r
_
Q2
6
Magnetic forces
Between two magnets or between a magnet and another piece of magnetic material there
are magnetic forces
N
F
S
F
F
F
N
S
N
S
N
Unlike poles attract each other
S
Like poles repel each other
Drag ( Solid – fluid contact force)
When an object is moving through fluid (liquid or gas) it experiences an opposing force called
drag.
The drag caused when an object moves through air is called air resistance.
air resistance
air resistance
upthrust
Drag
v
weight
weight
W
1. Drag opposes the motion
2. Drag increases with speed of object
Upthrust
upthrust
Fluids exert pressure on immersed object. The bottom of an
immersed object experiences greater fluid pressure than the
top. The pressure difference between top and bottom results
an upward force called upthrust.
P1
P2 > P1
P2
Newton’s third law
When a body A exerts a force on body B, body B exerts an equal and opposite force on body
A.or
Every action has an equal and opposite reaction.
7
Combining forces / Adding forces
(1) Resultant force
It is a single force that could replace all forces acting and have the same effect.
1. Two forces acting in the same direction
10N
=
15N
5N
2. Two forces acting the opposite direction
5N
=
10N
5N
3. Tow force acting at an angle to each other
The parallelogram rule
If two forces acting at a point are represented in magnitude and direction by two adjacent
sides of a parallelogram, their resultant force is represented in magnitude and direction
by the diagonal of the parallelogram form the point.
3N
30
3N
R
30
5N
5N
1cm = 1N
Newton’s second law of motion
The acceleration of a body is proportional to the resultant force and takes place in the
direction of the force.
Centre of gravity or centre of mass
The point (G) where all the weight of a body appears to act.
G
W
G
8
Centre of mass of a plane lamina
1. get a flat object , stand and a plumb line.(a string with a
weight on it
1. Make/ punch 3 holes in the object/ lamina
2. Hang it from the hole( so it can swing freely) and attached the
plumb line to the same hole.
3. Hang a plumb line in the hole and mark the line it passes
through
4. Repeat the procedure(for all other holes) again to get another
line
5. Their intersection point is the centre of mass.
Stability of simple objects
The position of the centre of mass affects its stability. If the centre of mass of an object is low
,it is less likely that will tip over if we tilt it.To increase stability we should
1. increase the surface area
2.making the object shorter.
How to know if an object will not tip over after tilting it?
The vertical line through the centre of mass should be within the base.
The turning effect of a force
The moment of a force is a measure of the turning effect of the force about a particular point
.it is defined as follows.
moment of a force  force  perpendiculardis tan ce fromthe po int
about a po int
The principle of moments
When an object is in equilibrium ,the sum of the anticlockwise moments about any point is
equal to the sum of the clockwise moments about that point.
9
Ticker Tape Timer
A ticker tape timer consists of an
electrical vibrator which vibrates 50
times per second.
1. This enables it to make 50 dots
per second on a ticker-tape being
pulled through it.
2. The time interval between two
adjacent dots on the ticker-tape is called one tick.
3. One tick is equal to 1/50 s or 0.02 s.
The distance between dots on a ticker tape
1. The distance between two adjacent dots on a tickertape represents the displacement of the object in a tick (0.02 s).
2. If the object moves quickly, the dots are far apart. If the object moves slowly, the dots are
close to each other.
3. Figure below shows the ticker-tapes produced by a fast and a slow-moving object.
Example:
Diagram above shows a strip of ticker tape that was pulled through a ticker tape timer that
vibrated
at
50
times
a
second.
What
is
the
a.
time
taken
from
the
first
dot
to
the
last
dot?
b. average velocity of the object that is represented by the ticker tape?
10
Example:
The ticker-tape in figure above was produced by a toy car moving down a tilted runway. If the
ticker-tape timer produced 50 dots per second, find the acceleration of the toy car.
Terminal velocity. (sky Diving)
Action
results
Sky diver jumps from plane
He accelerates downwards
Weight is greater than air resistance
There is a resultant force downwards.
According to F=ma he accelerates.
He reaches terminal velocity
as speed increases air resistance increases
When air resistance and weight balance
There is no resultant force(no acceleration)
He falls at a constant speed called terminal velocity
Sky diver opens parachute
his air resistance increases (
Resultant force is upwards
He decelerates
His speed continues to decrease until air resistance
And weight are balanced .he then falls at a much
Lower terminal velocity.
11
)
Stopping distance
the distance travelled by a vehicle between the diver’s noticing the need to stop and the car
stopping.
Stopping distance is the sum of the two distances
Stopping distance = Thinking distance + Braking distance.
Reaction time (thinking time)
Reaction time is the length of time between the moment when the driver realizes that the
car must be stopped and the moment when he applies breaks.
Factors that affects the reaction time
Driver is tired or under the influence of alcohol or other drugs that slow reaction time.
Poor visibility
Thinking distance
Thinking distance is the distance a vehicle travels during the driver’s reaction time(while
driver is reacting before applying the brakes)
Factors that affect the thinking distance
The speed of a vehicle.
The reaction time of the driver.(tiredness,drugs,alcohol,old age)
Poor visibility.
Braking distance.
Braking distance is the distance the vehicle travels whilst braking.
Factors that will affect the braking distance are:
The Speed of the vehicle.
Condition of the tyres or breaks
Condition of the road (wet,icy,or oil spillage)
Mass of the vehicle
12
Hooke’s law

Extension of a spring (wire) is directly proportional to the
force (tension) up to the elastic limi (limitt of
proportionality).
Force/N
force  Extension
F  x
F  k x
extension
Extension /m
force
Limit of proportionality
Force is proportional to extension up to a certain limit. This limit is called as the limit of
proportionality.
Elastic limit
When a force is applied to a spring and then removed, the spring returns to its original length.
This will happen up to a limit, called the elastic limit.
Elastic material
A material is said to be elastic if it returns to its original shape and size when the stretching
force is removed
Plastic material
A material is plastic if it doesn’t return to its
original shape when the force is removed.
Force/N
Elastic bands
Rubber bands do not obey Hooke’s law.
Because the graph is not a straight line
through origin. Force is not proportional to
extension
13
Extension /m
Conditions for equilibrium
1. Forces on the object are balanced (
)
2. The principle of moments must apply
Work (scalar quantity)
Work done = force x distance moved in the direction of the force
unit
= Joules = J
Energy (E) (scalar quantity)
Energy is the ability of a system to do work. (unit J)
Types of energy
Gravitational potential energy
An object of mass m at a vertical height h above the ground has a gravitational potential
energy of mgh
G.P.E = mg h
y
m x
where m – mass
G.P.E /J
g – gravitational acceleration
gradient = mg
h – vertical height
height /m
Kinetic Energy (scalar quantity)
K .E 
1 2
mv
2
An object of mass m traveling at a velocity v has a kinetic energy of
14
1
mv 2
2
Law of conservation of Energy
Energy cannot be made or destroyed, but it can be changed from one form into another
Work done = Energy transferred
Power (P)
Rate of doing work is called power
Power 
work done
Energy transferred

time
time
unit of power = Js-1 = W (watts)
Efficiency
Efficiency
useful work out put
x 100 %
Energy input
Efficiency
Power out put
x 100 %
Power input
Density (scalar quantity).
Density =
mass
Volume
=
Unit
m
v
=
kg
= kgm-3
m3
1
Density is defined as mass per unit volume and usually symbolized by  (rho).
Density of water is 1000 kgm-3. This means that 1m3 of water has a mass of 1000kg.
15
Pressure (scalar quantity).
Pressure =
P=
P
F
A
Force
Area
The pressure is defined as the force per unit area.
Unit =
N
 Nm 2 =Pa (Pascal)
2
m
2
p
Const f
P
Const f
1/A
A
Const A
F
Pressure in liquids (fluids)
The pressure at a point h vertically beneath the surface of the liquid
of density  is given by hg.
 = hg
h
x
A
16
States of matter
There are three states of matter. Solid ,liquid and gas
17
Change of state from solid to liquid -- melting
Change of state from solid to liquid – boiling / Evaporation
Boiling - Change of state from solid to liquid at boiling point.
•Evaporation:. It is the escape of the more energetic particles from the surface of a liquid. If
the more energetic particles escape, the liquid contains fewer high energy particles and more
lower energy particles so the average temperature decreases.
•Evaporation can be accelerated by:
-increasing temperature: more particles have enough energy to escape
-increasing surface area: more molecules are close to the surface
-reduce the humidity level in the air: molecules in the water vapour return to the liquid at
around the same rate that particles escape the liquid, when the air is humid. If the air is less
humid, fewer particles are condensing.
-blow air across the surface: removes molecules before they can return to the liquid
Boiling
Evaporation
1.
2.
constantly occurs on the surface of liquids
18
Brownian motion.
19
Gas Laws
Boyle’s law
For a fixed mass of gas at constant temperature the pressure of the gas is inversely
proportional to its volume.
P
P
Pressure 
1
Volume
P=
V
P
1
P
V
k
V
1/
PV
V
P
PV = k
P1 V1 = P2 V2
Investigating Boyle’s law
Set up the apparatus as shown.
Measure the pressure and volume of the
trapped air.
Use a foot pump to increase the pressure.
Record a series of corresponding readings of
pressure and volume.
Tabulate the readings and plot a graph of
pressure against
If the graph is a straight line through the origin
V = A xl
Vl
Pressure Volume
/ Pa
/ cm-3
5
60
300
10
30
300
20
15
300
(When A is constant)
20
PxV
1/V
Precautions
Allow time between readings for the compressed air to return to room temperature and it
also allows time for the oil on the sides of the tube to run down the tube.
Throughout the experiment it is important to check that the temperature of the laboratory
remains constant.
Boyle’s law and kinetic theory
Q1) A balloon filled with air at a pressure of 10 atmospheres squeezed to 1/5 of its original
volume, what will be the new pressure of the air?
Pressure law
For a fixed mass of gas at constant volume, the pressure is directly proportional to the Kelvin
temperature (absolute temperature)
PT
P = const x T
P
k
T
P1 P2

T1 T2
Investigating Pressure law
set up the apparatus shown.
Submerge as much of the flask as possible in water.
Use a short length of tubing to connect to pressure gauge.
Measure the temperature and pressure.
21
Heat the water bath with a Bunsen burner.
For a range of temperatures, record a series readings of the pressure of the gas.
Plot a graph of pressure against temperature.
Pressure / Pa
-273°C
Zero – Pressure
Temperature / °C
-273°C = 0 k This temperature is called absolute zero, the lowest temperature theoretically
possible. Absolute zero is the temperature at which molecular motion stops and pressure of
all gases would be zero.
Kevin temperature = Celsius temperature + 273
Tk  Tc  273
Temperature / k
Precautions
1) Immerse the flask fully into the water.
2) Use a short length of tubing to connect to pressure gauge since the air init will not
get fully heated.
3) Remove the Bunsen burner and stir for some time before taking a reading.
4)
Pressure law and kinetic theory.
22
Q1) A tin can at 27°C is heated to 327°C. If the pressure inside the can was increased by 120
Pa find the initial pressure.
Charles’s law
For a fixed mass of gas at a constant pressure, the volume occupied by the gas is directly
proportional to its absolute temperature
23
24
25
Heat transfer
Heat energy is transferred from a hotter place to cooler place by conduction ,convection and
radiation.
Conduction
Thermal conduction is the transfer of heat energy through a substance without the substance
itself moving .they transfer energy through molecular vibration and electron diffusion.
Metals are good thermal conductors. Because their atoms are packed close together and
they have large number of free electrons.
Good conductors- copper , aluminium, iron, graphite.
Bad conductors – glass ,water, plastic ,rubber, wood,air,material containing trapped air (wool
,fibre glass , expanded polystyrene).
Double glazing.- two layers of glass with an air gap between
26
Convection
Convection is the transfer of heat through fluids by the upward movement of warmer, less
dense of fluid.
When a liquid or gas (fluid) is heated, the particles move faster, and the fluid expands,
becoming less dense. The warmer, less dense fluid rises above its colder denser surrounding.
As the warmer fluid rises; cooler fluid takes its place(/sinks).This circular movement of fluid
is called a convection current.
To heat the whole of an oven the heat source must be at the bottom.
To cool the whole of a fridge the cooler must be placed at the top.
Sea breezes.
27
Radiation
Radiation is the transfer of heat energy by infra-red(IR) waves
Dull black surfaces are good absorbers and good emitters of infra-red radiation but bad
reflectors.
Shiny surfaces are bad absorbers and bad emitters. They are good reflectors.
28
Static Electricity.
Charge (Q)
There are two types of charges.
Positive charge- charge on the proton
Negative charge – charge on an electron
Unit of charge is coulombs (C)
Normally atoms have equal number of protons and electrons.so they are neutral.
If an atom (object) gains extra electron, it becomes negatively charged.
If an atom loses electrons, it becomes positively charged.
Ionisation - Production of ions by addition or removal of electrons.
Electrostatic force.
The force between two charges is called electrostatic force.it depends on
The distance between two charges
The magnitude of the charges.
Like (similar) charges repel each other
Unlike (opposite) charges attract each other.
Conductors
Materials which allow electrons to flow through them are called conductors.(
)
Good Conductor – metals (silver, copper, aluminium) ,carbon
Poor conductors – water, human body ,earth , semiconductors, silicon ,germanium
Insulators
Materials which do not conduct charge are called insulators.(
Insulators – rubber, plastics ( PVC, polythene, Perspex,) ,glass , dry air.
29
)
Charging materials by friction.
When a polythene rod is rubbed with a dry cloth electrons are transferred from the cloth to
the rod. The rod gains electron and becomes negatively charged. The cloth loses electrons
and becomes positively charged.
Before rubbing
after rubbing
When a perspex rod is rubbed with a dry cloth electrons are transferred from the rod to the
cloth. The cloth gains electron and becomes negatively charged. The rod loses electrons and
becomes positively charged.
*Conductors can be charged by rubbing –but only if held by in insulating handles; otherwise
electrons are transferred between the conductors and the ground via the person’s body.
Earthing.
when a charge object is earthed it becomes neutral.
Attraction of uncharged object.
A charged object will attract an uncharged object close to it.
Charge a balloon by rubbing it against your sleeves and the balloon will cling to a wall.
Charge a comb/ by pulling it through your hair and the comb will pick up small pieces of
paper.
Records become charged when you pull them out of their sleeves, and will attract dust as a
result.
30
When a charged Perspex (positive)
rod is brought closer to a small piece of aluminium foil/paper free
electrons in the aluminium are pulled towards the positively
charged rod, the top end of the foil becoming negatively charged
while the bottom end is left with a net positive charge. The charge
rod attracts the top end of the foil and repels the bottom end. As
the top end is closer to the rod, the force of attraction is the
stronger of the two forces and foil is pulled towards the rod as a
result.(the rod induces a charge in the foil)
Uses of static electricity.
Electrostatic paint spraying.
The nozzle of the spray is connected to the positive terminal.
The paint becomes positively charged as they emerge from the nozzle.
Repulsion between the similarly charged droplets keeps the paint as a fine spray.
The object to be painted is connected to a negative terminal.
This method gives an even coat.
Less paint is wasted and really awkward spots(
) still get a good coat of paint.
Inkjet printers.
Photocopiers.
Electrostatic precipitators.(removing dust from smoke)
Problems with static electricity.(dangers of static electricity)
Lighting
Refuelling
An aircraft in flight may become charged by rubbing the air.
If a refuelling tanker approaches the plane on landing before the charges are removed a
discharging spark could cause an explosion.
31
The charge is removed safely by earthing the plane. A wire is attached to it to provide an
escape route for the charges
Television screen / computer monitors become charged with static electricity as they are
used. These charges attract light uncharged dust particles.
Our clothing can, under certain circumstances, become charged with static electricity. When
we remove the clothes there is the possibility of receiving a small electric shock as the charges
escape to earth.
Gold-leaf electroscope
Gold-leaf electroscope is used for
1. Detecting charges
When a positively charged rod is
brought close to the metal cap of an uncharged electroscope
electrons in the leaf and plate are attracted upwards towards
the cap leaving a positive charge on the metal rod and the
gold leaf. Theses like charges repel each other, so the leaf
rises
The bigger the charge on the rod, the greater the deflection of the gold leaf.
When a negatively charged
rod is brought close to the metal cap of an uncharged
electroscope electrons are pushed away from the cap and
down into the leaf and plate. The leaf and the plate become
negatively. Theses like charges repel each other, so the leaf
rises
Charging an electroscope
Uncharged electroscope
a negatively charged object
Touches the metal cap
32
electroscope is negatively
charged
Uncharged electroscope
a positively charged object
Touches the metal cap
electroscope is positively
charged
2. Testing for positive or negative
If a negatively charged object is brought towards the cap of a negatively charged electroscope
free electrons are pushed away from the cap and down into the leaf and the plate. This
increases the repulsion between the leaf and the plate, and the leaf rises even more
If a negatively charged object is brought towards the cap of a positively charged electroscope
fre
33
Electricity
Charge (Q)
Charge = Current x Time
Q=I t
The property that gives rise to electrical forces. Charge is either positive or negative.
= 1.6 x 10 -19C
(+) positive -
The charge on the proton
(-) negative -
The charge on the electron = - 1.6 x 10-19C
Unit of charge = coulomb (C)
.
Number of free electron 
total ch arg e
ch arg e of an electron
Current ( I )
Current 
I 
Rate of flow of charge is called current.
ch arg e
time
Q
t
Unit of current = Cs-1 = A (Amperes)
1A=1C/s
Q1) Calculate the charge that flows when a current of 25mA flows for 2 hour?
Q2) a charge of 10mC flows past a point in a wire in 4 seconds. Calculate the current flowing
in the wire and the number of electrons passing the point each second?
Cell
A Cell is device supplying electricity from two electrodes placed in a chemical.
+
Cu
e
-
Symbol
Zn

+ -
34
I
e
Battery -
Battery is a collection of cells connected together.
Battery of 3 cell
Battery of any number of cells
Direct Current (D.C)
The cell pushes the electrons in one direction. If the
e
I
electrons (current) flow in one direction in a circuit the
current is called D.C.
current
current
0,0
0,0
time
time
Alternating Current (A.C)
current
AC power supply pushes the electrons
+
first one way and then the other. The
0,0
-
symbol
A.C
tim
electrons in the circuit moves
backwards and forwards. The power supply still supplies energy but without the electrons
moving steadily in any one direction.
Potential difference (V) or Voltage difference or voltage
Potential difference 
V 
work done
ch arg e
W
Q
unit JC 1  V (volt)
Voltage is the energy transferred per unit charged passed
One volt = one joule per coulomb
35
Q. In 10 sec a charge of 25C leaves a battery and 200J of energy is delivered to an outside
circuit as a result.calculate
a .the p.d across the battery
b .the current flows from the battery
Ohm’s law
A current through an ohmic conductor is directly proportional to the potential difference
across it provided the temperature and other physical conditions remain constant
V  I
R - Constant
V  IR
R – Resistance (of the conductor)
I
V
gradient 
V
R
I
I
V
Resistance
Resistant is a property of a component that opposes the current flow
R 
V
I
Fuse
= VA-1 = Ω (ohm)
Variable resistor
Fixed resistor
Resistance of a conductor depends on
1. Length of the conductor (l) ,
Cross sectional area of the conductor (A)
Material of the conductor and temperature.
36
Series circuits
V
Components are connected so that
I
I
V1
V2
1. the same current through each component
2. the total voltage is equal to the sum of the voltage
V3
across each component.(the larger the resistance of
the component,the bigger its share of voltage
Parallel circuit
Components are connected so that
V
1. the voltage across each component is the same
V
2. the current splits.
V
I
V
I
Series circuits
Parallel circuit
one switch can turn all the
switches can be placed in different parts of the
components on and off together.
Circuit to switch each bulb on and off
individually , all together.
If one bulb breaks ,it causes a gap
If one bulb breaks,only the bulbs on the same
In the circuit and all of the other bulbs
branch of the circuit will be affected.
Will go off.
When more bulbs are added in series
if more bulbs are added to a circuit in parallel
They all become dimmer(as voltage is
they all stay bright.
Shared in parallel circuit.
37
Ammeter
voltmeter
It is used to measure the current.
voltmeter is used to measure the p.d
across a component
It is connected in series.
It is connected in parallel.
An ideal ammeter has zero resistance.
An ideal voltmeter has infinite
resistance.
Power output of a battery / Power dissipated in a resistor
Power = volrge x current
P  VI
Unit – watts ( W )
Electric Energy
KWh is the unit of energy
Energy  Power x time
1kWh = 1unit
EPx t
1kWh = 103 W x 60 x 60 s
= 3.6 x 106 Ws
1kWh = 3.6 x 106 J
38
Ohmic conductor – which obeys ohm’s law
I
V
V
I
Filament lamp
V
I
V
I
Thermistor
It is made of semiconductor
A thermistor is a temperature sensitive resistor.
its resistance decreases with temperature.
Resistance
As it becomes warm the thermal vibration of
the lattice frees more charge carriers so
reducing its resistance.
temperature
Thermistors are often used in temperature
thermostats.
39
Sensing circuits such as fire alarms or
Light dependent resistor (LDR)
LDR is a light sensitive resistor
Resistance
when intensity of light increases its resistance
decreases (when it is in the dark its resistance is
high). This happens because the incident light frees
Light intensity
more charge carriers.
LDR is used in light sensing devices ( Burglar alarms Automatic lighting controls)
Diode
or
The diode allows current to flow freely in one direction only. This is called the forward
direction (or it is said to be forward biased)
I
Diode is forward biased.
Diode is reverse biased
(its resistance is small).
(its resistance is large)
In the reverse direction, very little current flows
I
A diode is a non – ohmic conductor.
0.6
40
V
Diode can be used to change alternating current into direct current
D.C
A.C
Light emitting diode (LED)
The LED has characteristic that are very similar to an ordinary semiconductor diode.
But it emits light when it conducts.
Conventional current –the direction in which positive charges would flow
41
Three pin plugs.
When wiring a plug it is important to check that the three wires in the cable are connected
to the correct terminals. The cable colour code is given below.
Live - brown
Neutral – blue
Earth - yellow and green (or just green)
The live wire.
The live wire alternates between a high +ve and –ve voltage of about 230V .the switch and
the fuse are fitted in the live wire.
The neutral wire
The neutral wire is always at 0 The electricity board earths the neutral wire by connecting it
to a metal plate buried in the ground.
electricity normally flows in through the live wire and out through the neutral wire.
The fuse
This usually consists of a small cylinder or cartridge containing a short piece of thin wire which
overheats,melts breaks if current of more than a certain value flows through it.
Fuse values
Fuses should be rated as near as possible but just higher than the normal operating current.
42
Earth wire
This is a safety wire which connects the metal body of the electrical appliance to earth and
prevents it becoming live if a fault develops.
If a fault develops in which the live wire somehow touches the metal case, then because the
case is earthed ,a big current flows in through the live through the case and out down the
earth wire.
This surge in current blows the fuse (or trips the circuit breaker) , which cuts off the live
supply.
This isolates the whole appliance ,making it impossible to get an electric shock from the case.
It also prevents the risk of fire caused by the heating effect of a large current.
Double insulation
If the appliance has a plastic casing and no metal parts showing then it’s said to be double
insulated. Anything with double insulation like that doesn’t need an earth wire.-just a live
and neutral.
43
Magnetism and Electromagnetism
Magnets
1. Bar magnet
2. Horseshoe magnet
Strongest parts of a magnet are called its poles.
Magnets have two poles: a north pole and a south pole.
The direction of magnetic field is from north to south.
A bar magnet suspended horizontally will align itself with the Earth’s magnetic field so that
its North points its north and its South pole points south.
Like poles repel each other and unlike poles attract each other.
Magnetic fields
The volume of space around a magnet, where magnetism can be detected is called a
magnetic field.
The shape of the magnetic field can be seen using iron filings or plotting compasses.
Magnetic field is invisible and found around magnets, planets and wires carrying current.
Magnetic fields exert a force on
1. magnetic material.( Magnets attract magnetic materials such as Nickel, Cobalt, iron
,steel)
44
2. other magnets
3. a wire carrying an electric current provided field and current are not parallel
4. Moving charges if they are not parallel to the field
Magnet do not attract non-magnetic material,e.g.wood ,plastics ,copper,aluminium.
The shape, strength and direction of magnetic fields is shown using magnetic lines of force.
The lines are close together where the field is strong.
The lines are far apart where the field is weak.
Magnetically soft materials
A Magnetically soft material is easy to magnetise and easily loses its magnetism.e.g iron
Magnetically hard materials
A Magnetically hard material is little difficult to magnetise but once it is magnetized it holds
onto its magnetism. Steel is a magnetically hard material. Some permanent magnets are
made from steel.
Plotting magnetic field lines
1 . Using iron filings
Place a bar magnet under a paper
Sprinkle iron filings on the paper
Tap the paper gently.
45
2. Using a plotting compass
A plotting compass is placed near one end of the
magnet, and a pencil dots are made on the paper to
mark the positions of the ends of the needle. The
compass is then moved so that its needle lines up with the previous dot made ,and so on.
Uniform magnetic field
x - Neutral point
A neutral point is a Position within overlapping
magnetic fields where the fields cancel so that
the resultant magnetic field is zero.
46
Electromagnetism
When a current flows through a wire a magnetic field is created around the wire .this
phenomenon is called electromagnetism.
The magnetic field due to current in a straight wire
If a current is passed through a wire, a weak circular
magnetic is created around the wire.
To make the magnetic field stronger we can increase the current or make the wire in to coil.
The right hand grip rule can be used to
determine field direction.
Point the thumb of your right hand in the
direction of the current and your finger
will curl in the direction of the magnetic
field.
The magnetic field around a flat coil
47
The magnetic field around a solenoid
A solenoid is a long coil.
The magnetic field around a coil or solenoid is
the same shape as that of a bar magnet.
The strength of the magnetic field around a
solenoid can be increased by
1 increasing the current flowing through the coil
2 increasing the number of turns on the solenoid.
3 wrapping the solenoid around a magnetically soft core such as iron
The positions of the poles for a solenoid can be found using the right hand grip rule.
wrap your finger in the direction of the current in
the coils and your thumb will point to the North
pole of the solenoid.
Electromagnet.
If a solenoid is wrapped onto a core made from a material such as iron, the strength of its
magnetic field increases. This combination of coil and core is called an electromagnet. One
of the main advantage of an electromagnet over a permanent magnet is that it can be turned
on and off.
-this combination of soft iron core and solenoid is often referred to as an electromagnet.
48
The Force on a current carrying conductor in a magnetic field
A current carrying conductor in a magnetic
field experiences a force provided the conductor is
not parallel to the field. The force has its maximum
value when the conductor is perpendicular to the
field.The force depends on,
1. The strength of the magnetic field (B)
2. The size of the currents (I)
3. The length of the conductor within the magnetic
field (l)
An increase in any of these three produces an increase in the magnitude of the force acting.
The direction of the force can be found using Fleming’s Left Hand Rule.
Flemings Left Hand Rule
If the first and second fingers and the thumb of the left
hand are placed at right angles to each other, with the first
finger pointing in the direction of the field and the second
finger pointing in the direction of the current , then the
thumb points in the direction of the force.
49
Q.The diagrams show three situation
involving a wire carrying a current
through a magnetic field .for each
situation find the direction of the stated
quantity.
Magnetic Force on a moving charged particle
A charged paraticle moving in a magnetic field experiences a force provided the field is not
parallel to the particle. The force has its maximum value when the particle moves
perpendicular to the field.
The direction of the force can be found using Fleming’s Left Hand Rule.
D.C electric motor
A simple motor to work from direct current consists of
a rectangular coil of wire mounted on an axle which can rotate between the poles of a Cshaped magnet. Each end of the coil is connected to half of a
split ring of copper, called a commutator, which rotates with
the coil. Two carbon blocks, the brushes,, are pressed lightly
against the commutator by springs. The brushes are
connected to an electrical supply. if Fleming’s left hand rule is
applied to the coil in the position shown, we find that side ab
experiences an upward force and side cd a downward force. These two forces form a couple
which rotates the coil.
50
Moving coil loud speaker
The cylindrical magnet produces a strong
radial magnetic field at right angles to the wire in
the coil. The coil is free to move backwards and
forwards and is attached to a stiff paper or plastic
cone. The loud speaker is connected to an
amplifier which gives out alternating current .since
the alternating current through the wire changes
direction it experiences a backward and forward
force .as a result; the cone vibrates and gives out
sound waves.
Electromagnetic induction
Production of electricity by the relative motion between magnetic fields and conductors.
This is the principal of generators and transformers.
When a conductor cuts the magnetic fields an e.m.f
/voltage is induced. Induced voltage depend on
Magnetic field strength
Speed of motion of the magnet or coil
Length of wire
Number of turns in the coil
51
52
Transformers
An alternating voltage applied to the primary produces an alternating current through the
primary coil. a changing magnetic field is produced which cuts the secondary coil since the
soft iron core traps most of the magnetic field .there is now a rate of change of magnetic flux
linkage in the secondary coil and an alternating voltage is induced in the secondary coil due
to electromagnetic induction ..
Vp - primary voltage
VS
N
 S
VP N P
V s - secondary voltage
Np - number of turns on secondary coil
Ns - number of turns on secondary coil
Ip – primary current
Is - secondary current
If Ns > Np, then Vs > Vp , this type of transformer is called a step up transformer.
If Ns < Np, then Vs < Vp , this type of transformer is called a step down transformer.
If the transformer is 100 % efficient, it is an ideal transformer.
So the Power input = Power output
Vp I p = Vs I s
53
The national grid
As the electrical energy travels through a cables some of it is wasted. It is changed into heat
and warms the cable. If the electrical energy is transmitted with a high voltage and a small
current, this loss is small.
Uses of electromagnet
The electric bell
When the bell push is pressed the circuit is
complete and the electromagnet becomes
magnetized. The soft iron armature is
pulled towards the electromagnet and the
hammer hits the gong. At the same time a
gap is created at the contact screw. The
circuit is incomplete and current stop
flowing. The electromagnet is turned off.
The spring’s armature returns to its original
position and the whole process starts again.as long as the bell push is pressed , the armature
will vibrate back and forth striking the gong.
54
Circuit breaker
The
circuit
breaker
uses
an
electromagnet to cut off the current if it
becomes larger than a certain value. If the
current is too high the electromagnet
becomes strong enough to pull the iron
catch out of position so that the contacts
open and the circuit breaks. Once the
problem in the circuit has been corrected the catch is repositioned by pressing the reset
button.
The relay switch
This is a safety device .it is often used to
turn on a circuit through which a large
current (which is danger of the user
receiving a severe electric shock) passes
using a circuit through which a small
current passes. When the switch s is
closed a small current flows turning the
electromagnet on. The. Iron armature is
attracted and at the same time the
contacts are pushed together. A large
current now passes through the second
circuit. If the switch s is open the
electromagnet is turned off ,the iron armature moves back to its original position. The
contacts open and current ceases to pass through the second circuit.
55
56
Waves
Travelling waves or Progressive Waves
WAVES
A wave is a disturbance which transfers
Mechanical
Waves
energy and information from one point to
another without transferring matter (By
Transverse
Waves
Electromagnetic
Waves
Longitudinal
Waves
Transverse
Waves
vibration)
Mechanical waves
Mechanical waves are produced by a disturbance,e.g. vibrating object, in a material medium
and are transmitted by the particles of the medium vibrating to and fro. There are two types
of mechanical waves:
1.Transverse waves
2.Longitudinal waves
Transverse Waves
direction of propagation
direction of
vibration
A wave where the displacements (vibrations) are perpendicular to the direction of travel of
the wave.
Amplitude
The maximum displacement of the wave from the equilibrium position.unit-
57
Wave length ( λ lamda)
The minimum distance between two successive crests or troughs.unit
Time period (T)
frequency 
The time taken to generate one complete wave.unit-
1
Time period
Frequency (f)

The frequency is the number of complete
Waves
1
T
generated per second
Unit Hertz- Hz
wave speed(v)
wave seed = frequency x wavelength
v = f
Q1) displacement (cm)
5
-5
30
15
time (min)
a.
Calculate the frequency of the wave.
b.
The wavelength of the wave is 2 cm. Calculate the
wave speed.
Longitudinal Waves
Waves in which vibrations are parallel to the direction
direction of travel

of travel of wave e.g. sound waves.as a result a
longitudinal wave consists of a series of compressions
.
( C ) and rarefactions ( R )
C - compression
R - rarefaction
wavelength is the distance between two successive compressions or rarefactions
58
Electromagnetic waves
Electromagnetic spectrum
-rays
X-rays
Ultraviolet
Visible
Light
UV
Infrared
Microwaves Radio
waves
IR
VI BGY O R
 increases
f decreases
Properties of Electromagnetic waves
1. All electromagnetic waves travel at the same speed of 3 x 108 ms-1 in vacuum or air.
2. All are transverse waves.
3. They do not need a medium to travel or they can travel through vacuum.
EM Waves
Source (Produced by)
 - ray
Radioactive nucleus
Uses
Sterilizing equipment and food
Radiotherapy
X – ray
Bombarding metals
Targets
with
high
X-raying people and materials (To
energy
broken
bones)To
kill
cancerous cell
electrons
UV – ray
detect
Extremely hot objects (sun)
detecting invisible marking
sterilizing,sun-tanning,fluorescent
lamps
Visible light
Very hot objects
Seeing,optical fibres,photography
59
Infra-red
Hot objects
Remote
controls,Night
vision
eqipment
Infra-red
cookers
and
heaters,
Short-distance communication
Microwaves Klystrons oscillator
Mobile
phones
and
satellite
Communication ,cooking,Radar
Radio
Oscillating currents in aerials
waves
Broadcasting and communication
( radio,TV )
Effects of excessive exposure of the human body to electromagnetic waves
Microwaves : internal heating of body tissue
Infra – red : skin burns
Ultraviolet : damage to surface cells and blindness
Gamma rays :cancer, mutation
Wavefront
The Line joining all points across adjacent rays that have exactly the same phase .
A
C
The direction of travel of wave is perpendicular to
the wavefront.
B

Distance between two successive wave fronts is .
60
Reflection
Where waves hit and rebound from a barrier and remain in the same medium.
Laws of reflection
The angle of incidence equals the angle of reflection
The Incident ray,the reflected ray and the normal all lie in the same plane
Images created by a plane mirror
Properties of an image in a plane mirror
Image is the same size as the object.
The image is virtual.
The image is laterally inverted.
The image is as far behind the mirror as the object is in front.
Virtual image.
images ,through which rays of light do not actually pass and
Image cannot be formed on a screen.
61
Refraction
The change in direction of wave as it passes from one medium to
another in which it has a different speed.
r
glass
air
v = f
f same
i
i = angle of incidence
v
r = angle of refraction
When light travels from optically less dense medium to more dense medium its speed
decreases.It bends towards the normal
sin i
n
sin r
This constant is known as the refractive index of the medium
When light travels from optically more dense medium to less dense medium its speed
increases.It bends away from the normal
sin r
n
sin i
Medium Refractive index
Water
1.33
Glass
1.5
62
Total internal reflection
air
glass
r
When light passes at small angles of incidence from an optically
i i
dense to less dense medium both refraction and reflection take
i<c
place. As angle of incidence increases angle of refraction also
increases
r
i
c=
air
glass
i=c
At a certain angle of incidence the angle of refraction in the less
dense medium is 900. This angle of incidence is called the critical
angle (c).
air
glass
i i
i>c
If the angle of incidence is more than the critical angle all the
incident Light is reflected inside the denser medium. This is called
total internal reflection.
Total internal reflection can occur only when
i. light travels from an optically more dense medium to an optically less dense medium
ii. the angle of incidence is more than the critical angle (c )
The critical angle (c) is the angle of incidence which causes the angle of refraction to be 900
when light travels from optically more dense to an optically less dense medium.
n
63
1
sin c
One of the most important applications for total internal reflection is the optical fibre.
Optical fibres are used in telecommunications.
Optical fibres are used in endoscopes to see inside the body.
measuring refractive index of glass
place a glass block on a sheet of paper and draw the outline of
the block
shine a ray of light at an angle on to the glass block
mark the path of the ray into and out of the block
remove the block and join the points where the light entered and
left the glass block
draw the normals on a paper at the points where the ray enters and where it leaves
Measure the angle of incidence(i) and angle of refraction(r)
.use
sin i
1  2
sin r
to find the refractive index of glass
64
Water waves
Speed of water waves depends on depth of water (depth  , speed )
Frequency depends on speed of vibration of the source (if it is a ripple tank it depends on
speed of motor)
To check  use the equation v = f 
The ripple tank
It consists of a transparent tray containing
water,having a light source above and white
screen below to receive the wave images when
the small electric motor is turned on the wooden
bar vibrates which gives straight ripples if it just
touches the water.if the bar is raised and small
ball
fitted
to
it
circular
ripples
are
produced.continuous ripples are studied more
easily if they are apparently stopped (frozen ) by viewing the screen through a stroboscope(a
disc with equally spaced slits,which can be spun by hand
65
Diffraction
Diffraction is the Spreading out of waves as they pass through a gap (or pass an edge).
Amount of diffraction depends on the slit width and the wavelength of the wave.
There is greater diffraction with a smaller gap
There is greater diffraction with larger wavelength
Diffraction can occur when the width of the slit is comparable to the wave length of the
wave.
66
Dispersion
When white light passes through a glass prism ,the light splits into a range of colours.
White light is actually a mixture of colours rather than a single colour, and the prism refracts
these different colours by different amounts.
The effect described above is called dispersion,and the colour range produced is known as a
spectrum
Sound waves
Sounds are produced by objects that are vibrating.
This is a longitudinal wave.
Sound needs a material to travel through.(cannot travel through a vacuum )
Speed of sound in solid > speed of sound in liquid > speed of sound in air
Speed of sound in air is approximately 340 m/s this is much lower than the speed of light
(approximately 300000000 m/s)
Speed of sound depend on temperature.(speed of sound increases with temperature)
A plane which travels faster than sound is described as being supersonic.
The average person can only hear sounds that have frequency higher than 20 Hz but lower
than 200000Hz .this spread of frequency is called audible range or hearing range.
67
Pitch of sound depends on frequency.
Higher frequency – higher pitch
Loudness of sound depends on amplitude.
Larger amplitude – louder sound
68
The structure of an Atom
Matter is made up of smaller particles called atoms. Atoms are made up of sub – atomic
particles called neutron , protons and electrons. Protons and neutrons are bound together in the
nucleus. Electrons orbit the nucleus.
10-10m
.
Diameter of an atom =10-10m
atom
nucleus
10-15m
Particle
Diameter of a nucleus =10-15m
The Protons and neutrons are called nucleons.
Mass
Charge
Proton
1u  1.67  10 27 kg
1.6  10 19 C
Neutron
1u  1.67  10 27 kg
0
Electron
1u
 9.1110 31 kg
1840
Symbol
P
1
1
1
 1.6  10 19 C
0
0
n
u = atomic mass unit
1
e
-1
Normally atom is neutral. .
Proton Number or Atomic Number (Z)
The total number of protons in the nucleus of an atom. (If atom is neutral proton number is
equal to the number of electron)
Neutron Number (N)
A=Z+N
The total number of neutron in the nucleus.
Mass Number or Nucleon Number (A)
The total number of protons and neutrons in an atom is called its mass number.
69
If an element with a chemical symbol X has a mass number A an atomic number Z, its
A
X
nucleus is represented
by the symbol.
proton
4
For Example: 23
Protons
Neutrons
Protons
He nucleus
2
Na atom
Neutrons
Electrons
Electrons
11
At different times, scientists have proposed various descriptions or models of the atom.
following Thomson’s discovery of the electron in 1897, one of the first atomic models
proposed was the “plum pudding” model. In this model atom was assumed to be a sphere of
uniform positive charge with negatively charged electron spread through it. (it is like plums in
a pudding) In 1911 Geiger and Marsden performed Alpha particle scattering experiment under
the direction of (Ernest) Ruther ford, which led to a new model of the atom.
Alpha particle scattering Experiment
4
Lead
tube
Vacuum
4

Screen
He
2
2
(Coated with Zinc sulphide)
Alpha source
Thin gold foil
(Radium
source in
lead box)
1) A thin gold foil was bombarded with alpha particles.
2) Alpha particles leaving the foil were detected by observing flashes of light (which they
caused on a glass screen coated with zinc sulphide.
70
71
Radioactivity
In 1896 (a Frenchman named) Henri Becquerel noticed some photographic plates which had
been placed close to a uranium compound, had become fogged. This effect is known as
radioactivity.
Radioactive decay is the process by which an unstable nucleus changes spontaneously into a
more stable one, through emission of ionising radiation.
There are three main types of nuclear radiation.
1) Alpha 24 2) Beta ( beta minus
0
1
 , beta plus 10 )
3) Gamma 00
The Emission of radiation both spontaneous and random .
random -you cannot predict when a particular nucleus will decay. (It is like throwing dice).
Spontaneous - Radioactive properties are not affected ( controlled ) by chemical or physical
conditions such as temperature and pressure.
Alpha decay
An Alpha particle is the nucleus of a helium atom and is made up of two protons and two
neutrons. It can be represented as He 
Rn + 
Ra
When a nuclide decays by alpha emission it
becomes a nuclide with an atomic number 2 less than
before and a mass number four less.
Proton
88
---
86
Neutron
138
---
136
Mass Number
226
---
222
72
0
Beta Decay ( Beta- minus
1 
)
Beta particle is a fast moving electron. It is written as
Sr
Y
e or
00
11

+
In beta minus decay, a neutron in the nucleus splits up into a proton
plus an electron. The proton stays in the nucleus ;the electron is
ejected at high speed it is a beta- minus particle.
n
p +

When beta minus decay occurs, the number of nucleon stays the same.
The number of proton goes up by 1.
The number of neutrons goes down by 1.
Beta- plus decay (positron) 10 (positive electron)
In beta plus decay a proton in the nucleus splits up into a neutron plus a positron.
C
Z 6
B +
------
5

When beta plus decay occurs,
The mass number stays the same.
A 11 -----N 5
------
11
6
The number of neutrons goes up by 1
The number of protons goes down by 1
Gamma Radiation
After emitting alpha or beta radiation, a nucleus may have surplus energy. It gives out this
energy by emitting electromagnetic radiation .these photons of radiation are called gamma
() rays.
Ionization – production of ions by removal or addition of electrons
73
Alpha radiation is heavily ionising. Because
1) Alpha particle has two positive charges.
2) Speed of alpha particle is less (than So when it travels it spends more time with
an atom.
When, at the end of its path , an alpha particle stops, its picks up two electron and becomes
a helium atom.
Summary Of the nature and properties of alpha, beta and gamma radiation
 - Radiation
 - Radiation
 - Radiation
4
Nature
Helium nucleus
He
Fast moving electron Short wave length
2
electro magnetic
radiation
(2 protons & 2
neutrons)
Charge
2+
1-
0
Mass
4(u)
1u 
0 

0
9
C
10
C=3x108ms-1
 1840 
Speed
1
C
10
C – speed of light
Penetrating
Least penetrating
More penetrating
power
stopped by thin
than  but less than
sheet of paper
 stopped by 5mm Al
(5cm in air)
sheet
74
Most penetrating
Ionising power
Highly ionising
Much less ionising
Very little ionising
than  but greater
than 
Deflection by
Small deflection
Very large deflection No deflection
magnetic field or
electric field
All three radiations are detected by photo graphic film, cloud chamber, Geiger – muller
tube. (G- M tube)
Activity (A) Rate of decay
The number of atoms of a source that decay per second is called the activity of the source.
Unit = s-1 or Bq (Becquerel)
B ecquerel - The unit of nuclear activity. One Becquerel is equivalent to one decay per
second
Half- life
The average time taken for half the radioactive nuclei of a radioactive substance to decay.
or The average time taken for the activity to fall to 50% of its original value.
e t
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Background radiation
Radiation which is constantly present in our environment is called background radiation.
.it is emitted from a variety of natural and artificial sources,(largely from natural sources).
It varies randomly with time.
Background count -
0.5-30 counts per second
Natural Sources of Background radiation
Artificial Sources of
Background radiation
1) Cosmic Rays (from outer space)
1) X-rays
2) Radio active rocks (uranium deposits in the ground)
2) nuclear power and
weapons
3) Radon gas emitted from the ground
4) Naturally occurring radioactive isotopes present in
our food and drink
Measuring background radiation
1) Place a G – M tube connected to a counter.
2) Measure the counts for 5 minutes in the absence of the source.
3) Repeat it twice. Find the average background count rate.
Safety precautions ( when using radioactive materials)
Do not touch radioactive material-use a handling tool
Keep sources in their lead storage containers when not in use.
Keep as far away as possible from all laboratory sources of ionizing radiation
Wash hands after working with a radioactive sources.
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Investigating Alpha, Beta and Gamma radiations
Place a G.M tube connected to a counter.
Measure the average background count rate in the absence of the radioactive source.( 20
counts/m)
Place the radioactive source less than 5cm from the G.M.tube and Measure the count
rate.(800 counts/min)
Investigating Alpha radiation
Insert a piece of paper between the source and the G.M tube and measure the count rate.
If the count rate falls to background count rate the source emits only alpha.(20 counts per
minute)
If it remains the same no alpha parcels are emitted.(800 counts per min)
If count rate is decreased but not to background count rate (Eg: 500) the alpha and some
other radiation are present.
OR
Move the source more than 5cm from the G.M.tube.
If the count rate falls suddenly to background count rate then the source emits only alpha
particles.If the count rate does not change (nearly same)  is not present.
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Investigating Beta
Insert 5mm thick Aluminium sheet. If the count rate falls to background count rate then
only beta is emitted.
If there is no change in count rate beta is not present. The source emits only Gamma.
If count rate decreases but not to background count rate beta and gamma radiations are
present.
* When 25mm lead is placed count rate decreases by half – if  is present.
Measuring half life
3cm
G.M.tube
Radioactive source
Counter
Place a G.M tube connected to a counter
Measure the background count rate in the absence of the source for 5 minutes.
Repeat it and find the average background count rate.
Place the source less than 5 cm from the G.M tube.
Measure the count rate at regular intervals for a certain period of time.
(Eg:- If half life of a radioactive source is 1 minute then record the counratet every 5 sec for
5 min.)
Calculate the corrected count rate and Plot a graph of corrected count rate against time.
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Uses of radioactive isotopes.
Radioactive materials have many uses in medicine, industry and agriculture.
Radioactive Tracers-the progress of a small amount of a weak radioisotope injected into a
system can be traced by a GM tube or other detectors. The method is used in medicine to
detect brain tumours and internal bleeding (to see if the thyroid gland is working properly
iodine-131) , in agriculture to study the uptake of fertilizers by plants, and industry to
measure fluid flow in pipes.
Radioactive tracers are used to detect leaks in underground pipes.
Radiotherapy- cobatl-60 emits high energy gamma rays and is used in the treatment of
cancer.
Strerilization – gamma rays are used to sterilize medical instruments by killing bacteria.
Food preservation – food goes bad and begins to rot because of the presence of microbes
or germs.if food is irradiated with gamma rays these germs are killed and food can be stored
for a much longer period of time.
Quality control
If the radioisotope is placed on one side of a moving sheet of material and a G M tube on the
other,the count rate decreases if the thickness increases. This technique is used to control
automatically the thickness of paper
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Carbon-14 dating
There are two isotopes of carbon. These are carbon-12 which is not radioactive (stable) ,and
carbon-14 which is radioactive(unstable).All living things have almost the same ratio of
radioactive carbon – 14 to stable carbon –12 as in the atmosphere. When they die no fresh
carbon is taken in and carbon -14 stars to decay with a half-life of 5700 years. So the fraction
of carbon -14 in their remains decreases. From the measurement of the ratio of carbon -14
to carbon-12 in the material such as wood ,linen the age of the archaeological remains can
be estimated.
Dating rocks
Nuclear fission
The process of splitting a nucleus is called fission.
If a neutron is shot into the nucleus of a uranium -235 atom, it becomes unstable and breaks
apart, producing two new lighter elements, some fast moving neutrons and a lot of energy.
235
92
Ur 
1
0
n

141
56
Ba 
80
92
Kr 
n  Energy
The three neutrons may hit other nuclei of
uranium,so causing the process to repeat. This is
called chain reaction. If this continues
uncontrolled ,too much energy is released too
quickly and an explosion results.nuclear
power stations make use of controlled fission
reactions to provide energy..Neutron is
used to split uranium because it has no
charge.
Uranium-235 is called fissile material because it goes through the splitting process easily.
Nuclear reactor
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Control rods
Control rods are made Boron or cadmium.
Control rods are used to control the rate of reaction
These absorb some of the ejected neutrons.
Pushing the control rods further into the reactor slows the reaction down.
Pulling the rods our a little increases the rate of reaction
When the rods are fully inserted into the core ,the chain reaction is almost stopped.
moderator
Graphite is used as moderator
moderator is used to slow down the emitted neutrons
this is because slow neutrons are more easily absorbed by uranium.
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