Electricity: GCSE questions with answers

Answer: C The rate of flow of electric charge

Current is the rate of flow of charge: how much charge passes a point each second. In metal wires the moving charges are electrons. Current is not a flow of energy, although the moving charges do transfer energy.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.2 Electrical charge and current

Answer: C A source of potential difference and a closed circuit

Charge only flows if there is a source of potential difference, such as a cell, and an unbroken (closed) circuit. In a single loop, current is not used up: it has the same value at every point.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.2 Electrical charge and current

Answer: A Charge = current × time

Charge = current × time (Q = I t), with charge in coulombs (C), current in amperes (A) and time in seconds (s). A current of 1 A means 1 coulomb of charge passes each second.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.2 Electrical charge and current

Answer: B Ohm (Ω)

Current is measured in amperes (A, or amps), potential difference in volts (V) and resistance in ohms (Ω). The current through a component depends on both the potential difference across it and its resistance.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.3 Current, resistance and potential difference

Answer: D Potential difference = current × resistance

Potential difference = current × resistance (V = I R). For a given potential difference, a bigger resistance means a smaller current. For a fixed resistor at constant temperature, the current is directly proportional to the potential difference.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.3 Current, resistance and potential difference

Answer: D The energy transferred per unit of charge

Potential difference is the energy transferred for each coulomb of charge that passes between two points (energy = charge × potential difference). So 1 volt is 1 joule per coulomb. Charge per second is current, and energy per second is power.

Checked against Pearson Edexcel GCSE Physics 1PH0 specification, 10.5 and 10.6 Potential difference

Answer: B A straight line through the origin

For some resistors the resistance stays constant as the current changes, as long as the temperature stays the same. Their current is directly proportional to the potential difference, giving a straight line through the origin. Lamps, diodes, thermistors and LDRs are not like this.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.4 Resistors

Answer: D It increases

A bigger current makes the filament of a lamp hotter, and the resistance of the filament increases as its temperature rises. So its current against potential difference graph is a curve that gets less steep.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.4 Resistors

Answer: B Lets current flow in one direction only

A diode lets current through in one direction only. In the reverse direction its resistance is very high, so almost no current flows. Its current against potential difference graph is flat for one direction and rises steeply in the other.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.4 Resistors

Answer: A It decreases

The resistance of a thermistor (the usual NTC kind) decreases as its temperature increases. Because its resistance depends on temperature, it is used in circuits that respond to temperature, such as thermostats.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.4 Resistors

Answer: A It decreases

The resistance of an LDR decreases as the light intensity increases. In the dark its resistance is high, so the current is small. Circuits use this to switch lights on when it gets dark.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.4 Resistors

Answer: A In parallel with the lamp

An ammeter goes in series with a component to measure the current through it; a voltmeter goes in parallel, across the component, to measure the potential difference. A variable resistor lets you change the current to take a range of readings.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.4 Resistors

Answer: D It is bigger than either resistor

In series, the total resistance is the sum of the resistances, so it is bigger than either. In parallel, the total resistance of two resistors is less than the smaller one on its own.

Checked against AQA GCSE Physics 8463 specification, 4.2.2 Series and parallel circuits

Answer: C It gives the charge an extra path to flow along

In series there is only one path, so every charge must pass through each resistor in turn, and the total resistance goes up. In parallel each extra branch is another path, so more charge can flow for the same potential difference and the total resistance goes down.

Checked against AQA GCSE Physics 8463 specification, 4.2.2 Series and parallel circuits

Answer: C It is the same through each component

In a series circuit the same current passes through every component, and the supply’s potential difference is shared between them. Since V = I R and the current is the same, the bigger resistance gets the bigger share.

Checked against AQA GCSE Physics 8463 specification, 4.2.2 Series and parallel circuits

Answer: B It is the same across each branch

In parallel, each branch is connected straight across the supply, so each has the same potential difference. The currents in the branches add up to the total current. Adding another lamp in parallel does not dim the others; the cell just supplies more current.

Checked against AQA GCSE Physics 8463 specification, 4.2.2 Series and parallel circuits

Answer: B Series has one path for the charge; parallel has two or more

In a series circuit the components are joined one after another in a single loop. In a parallel circuit they are on separate branches, so the charge has more than one path. Many circuits have both series and parallel parts.

Checked against AQA GCSE Physics 8463 specification, 4.2.2 Series and parallel circuits

Answer: C A light-dependent resistor (LDR)

Circuit symbols are standard. An LDR is a resistor box with two arrows pointing in (light falling on it). A diode is a triangle pointing at a bar, showing the one direction current can flow. In a cell, the longer line is the positive terminal.

Checked against AQA GCSE Physics 8463 specification, 4.2.1.1 Standard circuit diagram symbols

Answer: B The current through it and the potential difference across it

Resistance = potential difference ÷ current, so you measure the current with an ammeter in series and the potential difference with a voltmeter in parallel. A longer wire of the same kind has a bigger resistance, because charge must pass through more of it.

Checked against AQA GCSE Physics 8463 specification, 4.2.2 Series and parallel circuits

Answer: A a.c. at 50 Hz and about 230 V

Mains electricity in UK homes is an alternating current (a.c.) supply with a frequency of 50 Hz and a potential difference of about 230 V. The frequency means the direction reverses back and forth 50 times a second.

Checked against AQA GCSE Physics 8463 specification, 4.2.3.1 Direct and alternating potential difference

Answer: B Keeps changing direction

A direct potential difference stays in one direction, so it drives a direct current (d.c.), with charge flowing one way only, as from a battery. An alternating potential difference keeps reversing, so the current keeps changing direction (a.c.), as in the mains.

Checked against AQA GCSE Physics 8463 specification, 4.2.3.1 Direct and alternating potential difference

Answer: A Carries the alternating potential difference from the supply

The live wire carries the alternating potential difference from the supply. The neutral wire completes the circuit. The earth wire is a safety wire: it stops the metal case of an appliance becoming live, and only carries a current if there is a fault.

Checked against AQA GCSE Physics 8463 specification, 4.2.3.2 Mains electricity

Answer: D About 230 V

The live wire is at about 230 V compared with earth. The neutral wire is at, or close to, earth potential (0 V). The earth wire is at 0 V and only carries a current if something goes wrong.

Checked against AQA GCSE Physics 8463 specification, 4.2.3.2 Mains electricity

Answer: D It is still at a high potential compared with earth

Your body is at earth potential (0 V), so touching the live wire puts about 230 V across you and a current flows through you, even if the switch is open. A direct connection from live to earth has very little resistance, so a huge current flows that can overheat wires and start a fire.

Checked against AQA GCSE Physics 8463 specification, 4.2.3.2 Mains electricity

Answer: D Power = potential difference × current

Power is the rate of energy transfer: the energy transferred each second. For any circuit device, power = potential difference × current (P = V I), and energy transferred = power × time. Power is measured in watts (1 W = 1 J/s).

Checked against AQA GCSE Physics 8463 specification, 4.2.4.1 and 4.2.4.2 Power and energy transfers in everyday appliances

Answer: C It doubles

Since P = V I, doubling the current at the same potential difference doubles the power. The energy a device transfers is power × time, so it transfers more energy the longer it is on.

Checked against AQA GCSE Physics 8463 specification, 4.2.4.1 and 4.2.4.2 Power and energy transfers in everyday appliances

Answer: A It heats up

When a current flows through a resistance, work is done and energy is transferred to the thermal store of the resistor, so it heats up. This heating is useful in kettles and toasters but wasted in most other devices.

Checked against Pearson Edexcel GCSE Physics 1PH0 specification, 10.22 to 10.24 The heating effect of a current

Answer: A The thermal store of the water

Appliances transfer energy electrically from the mains or from a battery’s chemical store. Heating devices such as kettles fill the thermal store of what they heat; motors, as in a fan, fill the kinetic store of what they turn. Some energy is always wasted, dissipated to the thermal store of the surroundings.

Checked against AQA GCSE Physics 8463 specification, 4.2.4.1 and 4.2.4.2 Power and energy transfers in everyday appliances

Answer: C The 2000 W kettle

A power rating tells you how much energy an appliance transfers each second. In the same time, a 2000 W kettle transfers twice as much energy as a 1000 W one. The energy transferred depends on both the power and how long the appliance is on.

Checked against AQA GCSE Physics 8463 specification, 4.2.4.1 and 4.2.4.2 Power and energy transfers in everyday appliances

Answer: A Increases the potential difference for transmission

The National Grid links power stations to homes with cables and transformers. Step-up transformers raise the potential difference for the transmission cables; step-down transformers lower it to a much smaller value for homes.

Checked against AQA GCSE Physics 8463 specification, 4.2.4.3 The National Grid

Answer: B The current is lower, so less energy is lost heating the cables

For the same power, a higher potential difference means a lower current. A lower current heats the cables less, so less energy is dissipated on the way. That makes the National Grid an efficient way to transfer energy.

Checked against AQA GCSE Physics 8463 specification, 4.2.4.3 The National Grid

Answer: D Electrons moved from the cloth to the rod

Rubbing two insulators together moves electrons from one to the other. The material that gains electrons becomes negatively charged; the one that loses them is left with an equal positive charge. Protons do not move; charge is moved, not made.

Checked against AQA GCSE Physics 8463 specification, 4.2.5.1 Static charge (physics only)

Answer: B They repel

Like charges repel and unlike charges attract, even without touching: this is a non-contact force. If enough charge builds up, electrons can jump through the air to an earthed object, which you see as a spark.

Checked against AQA GCSE Physics 8463 specification, 4.2.5.1 Static charge (physics only)

Answer: B A region where a charge feels a force

A charged object has an electric field around it: a region where another charge feels a force. The field is strongest close to the object and gets weaker further away, so the force between two charges is bigger when they are closer.

Checked against AQA GCSE Physics 8463 specification, 4.2.5.2 Electric fields (physics only)

Answer: D Each balloon is in the other’s field and feels a force

A charge placed in another charge’s electric field feels a force, which explains attraction and repulsion at a distance. When the field between a charged object and an earthed one is strong enough, charge flows through the air and makes a spark.

Checked against AQA GCSE Physics 8463 specification, 4.2.5.2 Electric fields (physics only)