2. ELECTRICITY
A – Units:
2.1 – use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V) and watt (W)
B – Mains electricity:
o Charge (Q) – electrons and protons have charge, in circuits the electrons have charge, so they move – measured in
coulombs (C)
o Time (t) – measured in seconds (s)
2.2 – understand how the use of insulation, double insulation, earthing, fuses and circuit breakers protects
the device or user in a range of domestic appliances
Hazards of electricity:
o Damaged insulation – contact with wire due to gaps in insulation = electric shock/ pose a fire hazard
o Overheating of cables – high currents pass through thin wire conductors wires heat up melt insulation fire
o Damp conditions – water can conduct electricity electric shock
Fuse:
Advantages of circuit breakers (MS):
o Thin piece of wire overheats and melts if current = too high
o Circuit breakers are resettable
o Fuse breaks current stops/ circuit switches off
o Work instantly
o Used so that the circuit cannot overheat if there is a fault
o Doesn’t require earth wire
o Fuse value should only be a little big bigger than the current
o More sensitive
Circuit breaker:
o Consists of automatic electromagnetic switch breaks circuit if the current rises over a certain value
o Better than fuse can be reset + operate faster
Earthing:
o The case must be attached to an earth wire
o Creates a safe route for current to flow in case of a short circuit
prevents electric shocks
o Earth wires have very low resistance so if a strong current surges
through the wires, the fuse breaks and disconnects
Wires:
o Live wire – alternates between positive and negative voltage of about 230V
o Neutral wire – always at 0V
o Earth wire (or fuse/circuit breaker) – safety stops you getting hurt (see last point of earthing)
(Double) insulation: How does an earth wire act as a safety feature (MS):
o Prevent people from touching exposed wires and
o Earth connected to metal casing
getting shocked
o If casing becomes live
o Double insulation is used when there is no earth
o Provides low resistance path to earth
connection
o If large current in earth wire
o Double insulation = plastic casing + no metal parts
o Fuse breaks/blows/melts
showing
o Circuit switches off/current stops
, 2. ELECTRICITY
2.3 – understand why a current in a resistor results in the electrical transfer of energy and an increase in
temperature, and how this can be used in a variety of domestic contexts
o Resistance causes transfer of electrical energy to heat energy
o Some components are designed to have a high resistance to make sure this happens
o For example, electrical heaters have lots of resistors to ensure a high resistance a lot of heat is produced
2.4 – know and use the relationship between power, current and voltage
o Power (watts) = current (Amps) x voltage (Volts)
o P=ɪxV
2.5 – use the relationship between energy transferred, current, voltage and time
o Energy transferred (J) = current (Amps) x time (secs) x voltage (Volts)
o E=ɪxtxV
2.6 – know the difference between mains electricity being alternating current (a.c.) and direct current (d.c.)
being supplied by a cell or battery
o Alternating current – current flows in different directions continuously
o Direct current – current which flows in one direction only
o Mains electricity = alternating current
o Cell/battery = direct current
C – Energy and voltage in circuits:
2.7 – explain why a series or parallel circuit is more appropriate for particular applications, including
domestic lighting
Series Parallel
End to end in one loop Components are connected to the power supply
in separate branches
Same current flows through every component Current is shared on each branch (sum of current
in separate branches = current throughout the
source)
Voltage is shared across each component (sum of p.d. Potential difference is same across every branch
across components = p.d. across the supply)
Resistance: RT =R1 + R2 1 1 1 1
Resistance: = + +
R T R1 R2 R 3
Removing one component = broken circuit Removing one component hardly effects the
others
o Lamps = connected in parallel dimmer lights when adding bulbs but keep voltage constant
o Voltmeters = always in parallel
Advantages of lamps in parallel rather than series (MS):
o Can be switched on separately others stay on when 1 bulb blows
2.8 – understand how the current in a series circuit depends on the applied voltage and the number and
nature of other components
A – Units:
2.1 – use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V) and watt (W)
B – Mains electricity:
o Charge (Q) – electrons and protons have charge, in circuits the electrons have charge, so they move – measured in
coulombs (C)
o Time (t) – measured in seconds (s)
2.2 – understand how the use of insulation, double insulation, earthing, fuses and circuit breakers protects
the device or user in a range of domestic appliances
Hazards of electricity:
o Damaged insulation – contact with wire due to gaps in insulation = electric shock/ pose a fire hazard
o Overheating of cables – high currents pass through thin wire conductors wires heat up melt insulation fire
o Damp conditions – water can conduct electricity electric shock
Fuse:
Advantages of circuit breakers (MS):
o Thin piece of wire overheats and melts if current = too high
o Circuit breakers are resettable
o Fuse breaks current stops/ circuit switches off
o Work instantly
o Used so that the circuit cannot overheat if there is a fault
o Doesn’t require earth wire
o Fuse value should only be a little big bigger than the current
o More sensitive
Circuit breaker:
o Consists of automatic electromagnetic switch breaks circuit if the current rises over a certain value
o Better than fuse can be reset + operate faster
Earthing:
o The case must be attached to an earth wire
o Creates a safe route for current to flow in case of a short circuit
prevents electric shocks
o Earth wires have very low resistance so if a strong current surges
through the wires, the fuse breaks and disconnects
Wires:
o Live wire – alternates between positive and negative voltage of about 230V
o Neutral wire – always at 0V
o Earth wire (or fuse/circuit breaker) – safety stops you getting hurt (see last point of earthing)
(Double) insulation: How does an earth wire act as a safety feature (MS):
o Prevent people from touching exposed wires and
o Earth connected to metal casing
getting shocked
o If casing becomes live
o Double insulation is used when there is no earth
o Provides low resistance path to earth
connection
o If large current in earth wire
o Double insulation = plastic casing + no metal parts
o Fuse breaks/blows/melts
showing
o Circuit switches off/current stops
, 2. ELECTRICITY
2.3 – understand why a current in a resistor results in the electrical transfer of energy and an increase in
temperature, and how this can be used in a variety of domestic contexts
o Resistance causes transfer of electrical energy to heat energy
o Some components are designed to have a high resistance to make sure this happens
o For example, electrical heaters have lots of resistors to ensure a high resistance a lot of heat is produced
2.4 – know and use the relationship between power, current and voltage
o Power (watts) = current (Amps) x voltage (Volts)
o P=ɪxV
2.5 – use the relationship between energy transferred, current, voltage and time
o Energy transferred (J) = current (Amps) x time (secs) x voltage (Volts)
o E=ɪxtxV
2.6 – know the difference between mains electricity being alternating current (a.c.) and direct current (d.c.)
being supplied by a cell or battery
o Alternating current – current flows in different directions continuously
o Direct current – current which flows in one direction only
o Mains electricity = alternating current
o Cell/battery = direct current
C – Energy and voltage in circuits:
2.7 – explain why a series or parallel circuit is more appropriate for particular applications, including
domestic lighting
Series Parallel
End to end in one loop Components are connected to the power supply
in separate branches
Same current flows through every component Current is shared on each branch (sum of current
in separate branches = current throughout the
source)
Voltage is shared across each component (sum of p.d. Potential difference is same across every branch
across components = p.d. across the supply)
Resistance: RT =R1 + R2 1 1 1 1
Resistance: = + +
R T R1 R2 R 3
Removing one component = broken circuit Removing one component hardly effects the
others
o Lamps = connected in parallel dimmer lights when adding bulbs but keep voltage constant
o Voltmeters = always in parallel
Advantages of lamps in parallel rather than series (MS):
o Can be switched on separately others stay on when 1 bulb blows
2.8 – understand how the current in a series circuit depends on the applied voltage and the number and
nature of other components
