Electricity

Question 1

What is the unit of electric current?

Answer 1

Ampere (A)

Question 2

Define potential difference.

Answer 2

The work done per unit charge; measured in volts (V).

Question 3

State Ohm’s Law.

Answer 3

V = I × R, where V is voltage, I is current, and R is resistance.

Question 4

What is the equation for charge flow?

Answer 4

Q = I × t, where Q is charge, I is current, and t is time.

Question 5

What is the equation for energy transferred using charge?

Answer 5

E = Q × V, where E is energy, Q is charge, and V is potential difference.

Question 6

What is resistance?

Answer 6

A measure of how difficult it is for current to flow through a component.

Question 7

What happens to resistance when resistors are added in series?

Answer 7

Total resistance increases.

Question 8

What happens to resistance when resistors are added in parallel?

Answer 8

Total resistance decreases.

Question 9

What is a thermistor?

Answer 9

A resistor that changes resistance with temperature; resistance decreases as temperature increases.

Question 10

What is an LDR?

Answer 10

Light Dependent Resistor; resistance decreases as light intensity increases.

Question 11

What is direct current (DC)?

Answer 11

Current that flows in one direction only.

Question 12

What is alternating current (AC)?

Answer 12

Current that continuously changes direction.

Question 13

What is the frequency of mains electricity in the UK?

Answer 13

50 Hz.

Question 14

What is the potential difference of mains electricity in the UK?

Answer 14

230 V.

Question 15

What is the purpose of the earth wire?

Answer 15

To protect the user by directing current to the ground if there is a fault.

Question 16

What is the purpose of the live wire?

Answer 16

Carries current to the appliance; has high voltage (230 V).

Question 17

What is the purpose of the neutral wire?

Answer 17

Completes the circuit and carries current away.

Question 18

Why is the live wire dangerous?

Answer 18

It carries a high potential even when the appliance is off.

Question 19

What is the power equation using voltage and current?

Answer 19

P = V × I.

Question 20

What is the power equation using current and resistance?

Answer 20

P = I² × R.

Question 21

What is the equation for energy transferred using power?

Answer 21

E = P × t.

Question 22

Why do appliances with motors have a high power rating?

Answer 22

Because they need a lot of energy to do work.

Question 23

How does a fuse work?

Answer 23

It melts when current is too high, breaking the circuit.

Question 24

What is a circuit breaker?

Answer 24

An automatic switch that stops the current if it becomes too large.

Question 25

What is the role of the national grid?

Answer 25

To transfer electricity from power stations to homes and businesses.

Question 26

Why is electricity transmitted at high voltage?

Answer 26

To reduce energy loss as heat in transmission cables.

Question 27

How does a step-up transformer work?

Answer 27

Increases voltage and decreases current for transmission.

Question 28

How does a step-down transformer work?

Answer 28

Decreases voltage for safe use in homes.

Question 29

What is the relationship between power input and output in transformers?

Answer 29

For an ideal transformer, power in = power out.

Question 30

Why is energy conservation important in the national grid?

Answer 30

To ensure efficient energy transfer and reduce costs.

Question 31

Is the live wire safe to touch when the appliance is off?

Answer 31

No, it can still carry a high voltage and cause electric shock.

Question 32

Do components in parallel have the same current?

Answer 32

No, current splits across branches; voltage is the same.

Question 33

Does resistance stay the same in all components?

Answer 33

No, some components (e.g. filament bulb) have changing resistance.

Question 34

Is more current always better?

Answer 34

No, too much current can overheat wires and cause damage.

Question 35

Does a fuse prevent all electric shocks?

Answer 35

No, it only protects the appliance by breaking the circuit if current is too high.

Question 36

Is AC more dangerous than DC?

Answer 36

Not necessarily, but AC can be more harmful due to its changing direction and high voltage.

Question 37

Do thicker wires have more resistance?

Answer 37

No, thicker wires have less resistance.

Question 38

Can energy be lost in transformers?

Answer 38

Yes, real transformers lose some energy as heat despite being efficient.

Question 39

What does a straight line on an I–V graph represent?

Answer 39

A constant resistance (Ohmic conductor).

Question 40

What does a curve on an I–V graph represent?

Answer 40

Changing resistance (non-ohmic conductor).

Question 41

How does the I–V graph look for a filament bulb?

Answer 41

Curves as current increases, showing increasing resistance.

Question 42

How does the I–V graph for a diode behave?

Answer 42

Current flows in one direction only after a threshold voltage.

Question 43

How can you find resistance from an I–V graph?

Answer 43

By calculating the gradient: V ÷ I.

Question 44

Why does resistance increase in a filament lamp?

Answer 44

Because the metal gets hotter as current increases.

Question 45

What is the gradient of a V–I graph for a resistor?

Answer 45

The resistance, since V = I × R.

Question 46

How do you recognise an ohmic conductor on a graph?

Answer 46

It shows a straight-line graph through the origin.