Calderglen High
S3 Physics
Magnetism and Electricity
What I should know and be able to do
Name ___________________
Class
___________________
1
  
What I Should Know
Magnetism
Magnetism is an invisible force that will act at a distance
Magnets attract MAGNETIC material such as iron, nickel and cobalt.
An invisible magnetic field exists around a magnet.
An electromagnet is a coil of wire wound on an iron core
An electromagnet becomes a magnet when a current flows through the coil
The strength of the electromagnet depends upon:
 The number of turns
 Current in the coil
 Length of Coil
I can state uses of electromagnets. e.g. door bell, electric motor
I can explain how an electric motor works
 Coil of wire between two permanent magnets
 Current flows in the coil through brushes
 Coil rotates due to interaction of permanent magnetic field and the
coils electromagnetic field
Electrostatics
I know the structure of the atom
Particle
Charge
Proton
Positive
Electron
Negative
Neutron
Neutral
Location
Nucleus
Orbit around nucleus
Nucleus
Atoms are electrically neutral because:
Number of Positive Protons = Number of Negative Electrons
Charge is built up when electrons are transferred between one substance and
another by rubbing
2
  
What I Should Know
An electric field is a region in which a charge experiences a force.
A Van De Graaff dome becomes positively charged when a rubber belt removes
electrons
A spark is seen when a metal sphere is brought close to the dome. This is
because negative charge moves through the field to the dome.
I can complete electric field diagrams
Current Electricity
Current is the movement of electrical charge around a circuit
Conductors allow current to pass through because there are free moving
electrons.
Metals are good conductors of electricity
Insulators do not allow current to pass through because there are no free
moving charges
Plastics, glass and air are good insulators
Charge is measured in coulombs
Current is measured in amperes
I understand and can use the relationship:
Current = charge / time
3
  
What I Should Know
Potential difference is a measure of the potential energy difference per
coulomb between two points in a circuit or an electric field.
Voltage is another word for potential difference
Potential difference is measured in volts
The voltage of a battery is a measure of the energy given to each coulomb of
charge that moves through it.
Batteries and solar cells produce direct current (D.C.). This electricity flow
only in one direction.
Spinning generators produce alternating current (A.C.). This changes direction
every fraction of a second.
Mains electricity is alternating current (A.C.).
 Mains voltage = 230V
 Mains frequency = 50 Hz
Simple Circuits
I can draw and label component symbols for:
Battery, fuse, resistor, capacitor, variable resistor, diode, lamp, switch
Current is measured using an ammeter. This must be placed in series.
Voltage is measured using a voltmeter. This must be placed in parallel.
Resistors
Resistance in the difficulty charges have in moving through a material.
Increasing resistance decreases the current.
Resistance is measured in Ohms (Ω)
I can use the relationship V = IR
Voltage = current X resistance
Variable resistors can be used to alter the current in a circuit.
4
  
What I Should Know
I can give examples of uses of variable resistors. e.g. volume control, dimmer
switch.
Electrical energy is converted to heat energy when there is resistance in a
wire.
I can state applications of this conversion to heat energy. e.g. kettles.
Variable resistors are altered by sliding contacts or rotary knobs
A thermistor’s resistance varies with temperature
Light dependant resistors vary with light level.
Power and Energy
Electrical power is the rate at which electrical energy is converted into other
forms
I can use the relationship P = E/t
Power = energy / time
(electrical power unit is Watts - W)
I can use the relationship P = IV
power = current X voltage
I can use the relationship P = I2R
Power = (current x current) x resistance
Series and Parallel Circuits
Series circuits have only one path. The current is the same at all points
Switches must all be closed in order for a series circuit to operate.
The supply voltage is equal to the sum of voltages across all components
Vs=V1 + V2….
The total resistance is equal to the sum of resistances in the circuit
Rs=R1 + R2….
Parallel circuits have parallel branches
5
  
What I Should Know
The total current drawn in a parallel circuit is the sum of the currents in each
branch
Is=I1 + I2….
The voltage is the same across each branch in a parallel circuit.
Parallel circuit: total resistance
I know how to use a continuity tester.
I can safely wire a plug
I know how a fuse protects a flex from overheating
I can select an appropriate fuse and flex for a particular power rating
I can explain how an earth wire acts as a safety device
I can explain why double insulated casings do not require an earth wires
I know why household circuits are in parallel
I can explain how a ring circuit works
I understand how a mains fuse works
I know the difference between a mains fuse and a circuit breaker
I can work out kilowatt hours (kWh) used for a given appliance over a set time
period
I can convert between kWh and Joules using the relationship E = Pt
6
Notes:
7