P2 - Electricity

Question 1

True or false? The current in a single closed loop of wire is the same at any point.

Answer 1

True

Question 2

What do the circuit symbols in the image represent?

Answer 2

A - a light-emitting diode (LED)
B - a fuse
C - a variable resistor

Question 3

What is the equation that links charge flow, current and time?

Answer 3

Charge flow = current x time
Or
Q = It

Question 4

True or false? For a given potential difference, the smaller the resistance of a component, the smaller the current through it will be.

Answer 4

False. Resistance if anything that slows down the flow of charge. So for a given potential difference, the smaller the resistance of a component, the greater the current through it will be.

Question 5

How can you calculate the resistance of a component if you know the potential difference across it and the current through it?

Answer 5

Divide the potential difference by the current. (V = IR, so R = V / I)

Question 6

True or false? A diode has a very high resistance in one direction.

Answer 6

True. The high resistance in one direction makes it very hard for a current to flow in that direction.

Question 7

What is the relationship between potential difference and current for an ohmic conductor at a constant temperature.

Answer 7

Current is directly proportional to potential difference for an ohmic conductor at a constant temperature.

Question 8

Name the component represented by the symbol.

Answer 8

A light-dependent resistor (LDR)

Question 9

True or false? Thermistors can be used in thermostats that control the temperature of a room.

Answer 9

True. They’re used in lots of devices that need to sense changes in temperature.

Question 10

True or false? All components connected in series will have the same size current flowing though them.

Answer 10

True. The current is the same at any point in a series circuit.

Question 11

How do you find the total resistance of a series circuit?

Answer 11

By adding up the resistance of each component in the circuit.
(You could also work out the total resistance by measuring the current through the circuit and the potential difference across all components, then using the equation V = IR)

Question 12

True or false? The current through all components connected in parallel is always the same.

Answer 12

False. The current is shared between the branches of a parallel circuit. The potential difference across all components connected in parallel is the same.

Question 13

Which will have a higher total resistance: two identical resistors connected in parallel, or the same resistors connected in series?

Answer 13

The resistors connected in series have higher resistance. (When you connect resistors in parallel you lower their total resistance).

Question 14

Each light in a house can be turned on and off without affecting other lights. Are the lights connected in series or parallel?

Answer 14

Parallel.

All the lights would turn on and off at the same time if they were connected in series.

Question 15

True or false? The potential difference across the components in a circuit is not affected by how the components are connected to the power supply.

Answer 15

False. The potential difference (pd) of components in series add up to the power supply pd but components connected in parallel to the supply have a pd equal to the supply pd.

Question 16

True or false? Adding resistors in series to a circuit should increase the total resistance if the circuit.

Answer 16

True.

Question 17

When investigating how connecting resistors in series or parallel circuits affects the overall resistance, why is it important to use the same equipment?

Answer 17

To keep the equipment a fair test. (Eg. Changing the equipment might introduce random errors)

Question 18

True or false? The frequency of the UK mains electricity supply is 230 Hz.

Answer 18

False. The frequency of the UK mains electricity supply is 50 Hz; the potential difference is 230 V

Question 19

Which wire in a three-core cable is covered in brown insulation?

Answer 19

The live wire.

Question 20

What is the potential difference between the live wire and the earth wire?

Answer 20

230 V

Question 21

True or false? Work is done when charges flow in a circuit.

Answer 21

True. Charges in a circuit do work against resistance.

Question 22

Give the equation that links energy transferred, charge flow and potential difference.

Answer 22

Energy transferred = charge flow x potential difference
Or
E = QV

Question 23

True or false. The power of a device depends on the potential difference across it and the current through it.

Answer 23

True. The power of a device is the product of these values.

Question 24

What is the equation that links power, current and resistance?

Answer 24

Question 25

What is the national grid? What is it used for?

Answer 25

A system of transformers and cables that connects power stations to consumers. It is used to transmit electrical power from power stations to consumers anywhere on the grid.

Question 26

True or false? The national grid efficiently transfers energy by transmitting electricity at a high current and a low potential difference.

Answer 26

False. It transfers the energy efficiently by using a high potential difference and a low current. This minimises the nearby dissipated by heating.