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OCR Additional Science
P4 Radiation for Life
AGAC
F
Equations for this unit (Foundation)
unit 5
unit6
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H
This slide shows
the equations
needed for this
Unit (Higher)
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unit 5
unit6
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Static Electricity
Static electricity is when charge “builds up” on an object and
then stays “static”. How the charge builds up depends on what
materials are used:
Rod becomes
Rod becomes
negatively
positively
charged
charged
-
+
-
+
-
+
+
-
-
+
It is only the negative charges
-the electrons which move
-
+
-
+
-
+
+
-
-
+
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attracted to duster
positive
negative
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Any three from:
Duster has gained electrons
Dust is positively charged
Dust has lost electrons
Opposite charges attract
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Static Electricity
+
+
-
+
-
-
Unlike charges attract
-
-
-
-
Like charges repel
-
-
Van de Graaf generators
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Use of static - Photocopiers
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+ + + + +
+ + + + +
1)
P
2)
3+4)
+ ++
+
+
+ ++
+
+
Photocopiers use static
electricity. They work by: 1)
image of the page
Copying an ______
onto a charged
______ plate, 2) Light
leak
then causes the charge to ____
away, leaving an “electrostatic
impression” of the page, 3) The
charges left on the plate
attract small drops of black
______
powder, 4) The powder is
transferred from the plate onto
paper 5) The paper is
the _____,
_____
heated to “fix” the powder.
Words – heated, leak, paper, image, charged, attract
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Uses of Static – Smoke Precipitators
Chimney
Negatively
charged
plates
Positively
charged
grid
-
-
-
-
-
+
+
+
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Uses and dangers of Static Electricity
Find out how static electricity is used in the following:
1) Laser printers
2) Paint sprayer
3) Defibrillators
Find out how static electricity is dangerous in the following
situations:
1) Fuel pipes
2) Hospitals
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positive/negative
negative/positive
attracted
knocked
These need to
be opposites
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F
shock or sparks
Wiring a plug
1. Earth
wire
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4. Live
wire
5. Fuse
2. Neutral
wire
3. Insulation
The neutral wire of a plug stays at
a potential close to zero relative
to the Earth
6. Cable
grip
The live wire of a plug alternates
between positive and negative
potential relative to the Earth
Fuses
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Fuses are _______
safety devices. If
there is a fault in an appliance
live and
which causes the ____
neutral (or earth) wire to cross
large current will flow
then a ______
through the _____
fuse and cause it
melt This will break the
to _____.
circuit and protect the
_______
appliance and user from further
harm
_____.
Words – large, harm, safety, melt, live, circuit, fuse
Earth wires
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Earth wires are always used if an appliance has a _____
metal
fault in the appliance, causing the live
case. If there is a _____
touch the case, the current “_______”
surges down the
wire to ______
fuse blows.
earth wire and the ______
Words – fuse, fault, metal, surges, touch
Circuit breakers
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Residual Current Circuit Breakers
(RCCBs) are often used with fuses. They
have some advantages over fuses:
1) They are safer – they don’t get hot
2) They react more quickly
3) They can be switched off for repairs
4) They are easy to reset
5) Each RCCB is attached to a certain
circuit, so if one switches off you can
see which circuit has a fault
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Resistance
Resistance is anything that will
RESIST a current. It is measured
in Ohms, a unit named after me.
Georg Simon Ohm
1789-1854
The resistance of a component can be
calculated using Ohm’s Law:
Resistance
(in )
=
V
Voltage (in V)
Current (in A)
I
R
An example question:
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Ammeter
reads 2A
A
V
Voltmeter
reads 10V
1) What is the resistance across
this bulb?
2) Assuming all the bulbs are the
same what is the total resistance
in this circuit?
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More examples…
3A
6V
12V
3A
2A
4V
2V
1A
What is the
resistance of
these bulbs?
Resistance
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Resistance is anything that opposes an electric current.
Resistance (Ohms, ) =
Potential Difference (volts, V)
Current (amps, A)
What is the resistance of the following:
1) A bulb with a voltage of 3V and a current of 1A.
2) A resistor with a voltage of 12V and a current of 3A
3) A diode with a voltage of 240V and a current of 40A
4) A thermistor with a current of 0.5A and a voltage of
10V
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Break in the circuit
12/1.5 (1)
=8
Waves- Some definitions…
1) Amplitude – this is
“how high” the wave is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
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Some definitions…
Transverse waves are
when the displacement
is at right angles to the
direction of the wave…
Just pick out one particle and follow its motion
Longitudinal waves
are when the
displacement is
parallel to the
direction of the wave…
Just pick out one particle and follow its motion
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Ultrasound
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Ultrasound is the region of sound above 20,000Hz – it can’t
be heard by humans. It can be used in pre-natal scanning:
How does it work?
Ultrasonic waves are partly _________
reflected at the boundary as they pass from
medium to another. The time taken for these reflections can be
one _______
depth of the reflecting surface and this
used to measure the _______
picture
information is used to build up a __________
of the object.
Words – depth, reflected, picture, medium
Other uses of ultrasound
1) Echo sounding
The ultrasound is reflected from the
sea floor.
2) Breaking down kidney stones
Ultrasonic waves break kidney
stones into much smaller pieces
3) Cleaning (including teeth)
Ultrasound causes dirt to vibrate
dirt off without damaging the object
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F
scans
to monitor pregnancy
break down kidney stones
measure blood flow
by measuring frequency change
cleaning instruments
treat cancer
by vibrating particles
makes dirt particles shake off
using an intense beam aimed at tumour
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frequency
vibrate
break up
The structure of the atom
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ELECTRON –
negative, mass
nearly nothing
NEUTRON –
neutral, same
mass as
proton (“1”)
PROTON –
positive, same
mass as
neutron (“1”)
The structure of the atom
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Particle
Proton
Relative Mass
1
Relative Charge
+1
Neutron
Electron
1
0
0
-1
MASS NUMBER = number of
protons + number of neutrons
SYMBOL
PROTON NUMBER = number of
protons (obviously)
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Introduction to Radioactivity
Some substances are classed as “radioactive” – this means that
they are unstable and continuously give out radiation:
Radiation
The nucleus is more stable after emitting some radiation – this
is called “radioactice decay” and the activity is measured in
“Becquerels (Bq)”.
Types of radiation
Unstable
nucleus
New
nucleus
Alpha
particle
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1) Alpha () – an atom decays into a new
atom and emits an alpha particle (2
neutrons – the nucleus of a
protons and 2 ______
helium atom)
______
2) Beta () – an atom decays into a new
atom by changing a neutron into a
proton
_______
and electron. The fast moving,
beta
Beta high energy electron is called a _____
particle particle.
Unstable
nucleus
New
nucleus
Unstable
nucleus
New
nucleus
3) Gamma – after  or  decay surplus
______
energy is sometimes emitted. This is
called gamma radiation and has a very
frequency with short wavelength.
high ______
The atom is not changed.
Gamma
radiation
Words – frequency, proton,
energy, neutrons, helium, beta
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Changes in Mass and Proton Number
Alpha decay:
241
Am
95
237
93
Np
4
+
2
α
Beta decay:
90
Sr
38
90
Y
39
+
0
β
-1
Uses of radioactivity 1
Sterilising medical instruments
Gamma rays can be used to kill and sterilise
germs without the need for heating.
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Uses of radioactivity 2
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Beta
detector
Rollers
Paper
Beta
emitter
This is used to make sure the paper/steel is the correct thickness.
The pressure on the rollers is adjusted depending
on how much of the beta is received by the detector
Uses of radioactivity 3
Smoke detectors
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Alpha
emitter
+ve electrode
-ve electrode
Alarm
This sets off an alarm
This involves `a
NOT gate
See Unit 6
Ionised air particles
If smoke enters here a
current no longer flows
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Uses of Radioactivity 4 - Treating Cancer
High energy gamma radiation can be used to kill cancerous
cells. However, care must be taken in order to enure that the
gamma radiation does not affect normal tissue as well.
Radioactive iodine can be used to treat thyroid cancer. Iodine
is needed by the thyroid so it naturally collects there.
Radioactive iodine will then give out beta radiation and kill
cancerous cells.
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F
/
/
/
/
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F
tracer
decreases
nucleus
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focussed/directed at/concentrated
all of tumour receives the full dose
Healthy tissue does not
receive the full dose
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so gamma can reach the surface
low count rate after the blockage
Half life
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The decay of radioisotopes can be used to measure the
material’s age. The HALF-LIFE of an atom is the time
taken for HALF of the radioisotopes in a sample to decay…
= radioisotope
At start
there are 16
radioisotopes
After 1 half
life half have
decayed
(that’s 8)
= new atom formed
After 2 half
lives another
half have
decayed (12
altogether)
After 3 half
lives another
2 have
decayed (14
altogether)
A radioactive decay graph
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Count
1 half
life
1 half
life
1 half
life
Time
Dating materials using half-lives
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Question: Uranium decays into lead. The half life of uranium is
4,000,000,000 years. A sample of radioactive rock contains 7 times as
much lead as it does uranium. Calculate the age of the sample.
Answer: The sample was originally completely uranium…
1 half life
later…
1 half life
later…
1 half life
later…
8
8
4
8
2
8
1
…of the
sample was
uranium
Now only 4/8 of
the uranium
remains – the
other 4/8 is lead
Now only 2/8 of
uranium remains
– the other 6/8
is lead
Now only 1/8 of
uranium remains
– the other 7/8
is lead
8
So it must have taken 3 half lives for the sample to decay until only 1/8
remained (which means that there is 7 times as much lead). Each half
life is 4,000,000,000 years so the sample is 12,000,000,000 years old.
An exam question…
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Potassium decays into argon. The half life of potassium is
1.3 billion years. A sample of rock from Mars is found to
contain three argon atoms for every atom of potassium.
How old is the rock?
(3 marks)
The rock must be 2 half lives old – 2.6 billion years
Background Radiation
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13% are
man-made
Radon gas
Food
Cosmic rays
Gamma rays
Medical
Nuclear power
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Uses of radioisotopes - tracers
A tracer is a small amount of radioactive material used to
detect things, e.g. a leak in a pipe:
If there is a
Gamma
source
blockage we
know where it is
because there will
be no gamma
reading beyond it
The radiation from the radioactive source is picked up above
the ground, enabling the leak in the pipe to be detected.
Tracers can also be used to develop
better plant fertilisers and in
medicine to detect tumours:
Nuclear power stations
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These work by using nuclear fission reactions using uranium:
Nuclear fuel (uranium) is used to boil water in a “heat
exchanger”. The steam drives a turbine.
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F
uranium
produce
steam
Nuclear fission
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More
neutrons
Neutron
Uranium or
plutonium
nucleus
Unstable
nucleus
New nuclei
(e.g. barium
and krypton)
Chain reactions
Each fission reaction releases
neutrons that are used in
further reactions.
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nucleus
atom/nucleus
neutron
absorb neutrons
fission