What is the unit for current?
What is the unit for voltage?
What IS current?
the rate of flow of charge
What is the unit for energy?
What is the unit for resistance?
What IS voltage?
energy transferred per unit charge, joules per coulomb
What is the unit for power?
What is the equation for charge?
charge = current x time (Q=IT)
What is the equation for resistance, voltage and current?
voltage = current x resistance (V=IR)
What is the equation for power?
power = current x voltage (P=IV)
What is the equation for energy transferred?
energy transferred = power (IV) x time (E=PT)
Mains electricity has an...current
Batteries have a...current
What happens to the current when you increase the resistance?
less current can flow
What colour is the neutral wire?
What colour is the live wire?
What colour is the earth wire?
green and yellow
What are the safety features of a plug (the plug itself)?
- right coloured wire connected to each pin - no bare wires showing inside plug - cable grip tightly fastened over the cable outer layer - metal parts made of copper or brass (good conductors) - case, cable grip and cable insulation made of rubber or plastic (good insulators and flexible)
Order of wires in a plug?
neutral, earth, live
What does the neutral wire do?
current flows out of the neutral wire, which always has 0V
What does the live wire do?
current flows in via the live wire, which alternates between a high negative and positive (alternating) voltage of 230V
What does the earth wire do?
when there is a fault and the live touches the case, a large current builds up in the live, through the case and is sent down the earth wire.
Safety precautions when using plugs?
- damaged (missing/ cracked/ broken case) so that there aren't exposed live wires which could give you a shock - cable isn't frayed, exposed live wires - cables aren't too long, trip hazard - no water near electrics, good conductor - no metal objects in plug as good conductor
A plug with metal casing...
must be earthed to an earth wire so that the conductor can never become live
A plug with plastic casing...
is double insulated. Plastic is an insulator so stops current flowing. Doesn't need an earth wire.
What does a fuse do?
when a fault develops, a surge of current flows though the live and then the earth. This melts the fuse which cuts off the live supply. This isolates the appliance which means you can't get shocked and reduces the fire risk
What does a circuit breaker do?
when a circuit breaker detects a surge in current it breaks the circuit by opening a switch
What are the advantages of a circuit breaker over a fuse?
- works faster - doesn't have to be replaced, can be reset - works for small current charges which might not melt a fuse but are still dangerous
What is an RCCB?
residual current circuit breaker, detects a difference in current between the neutral and the live wire and cuts the circuit
What happens when electric current passes through a resistor?
there is a heating effect on the resistor which increases the resistor's resistance, meaning less current can flow.