GCSE Combined Science Electric circuits questions by topic

This question is about circuit meters and symbols.

1. (a)Name the instrument that measures current.[1]
2. (b)State how it is connected into a circuit.[1]
3. (c)Name the instrument that measures potential difference.[1]
4. (d)State how that instrument is connected.[1]

This question is about charge and current.

1. (a)Write the equation linking charge, current and time.[1]
2. (b)Calculate the charge moved when a 2.0 A current flows for 30 s.[2]
3. (c)State the unit of charge.[1]

A 12 V battery drives a current through a single 4 Ω resistor.

1. (a)Write the equation linking potential difference, current and resistance.[1]
2. (b)Calculate the current in the resistor.[2]
3. (c)State what happens to the current if a second 4 Ω resistor is added in series.[1]

This question is about parallel circuits.

1. (a)State the p.d. across each branch of a parallel circuit.[1]
2. (b)Branches carry 2 A, 1 A and 4 A. Calculate the supply current.[1]
3. (c)Two identical lamps are connected in parallel to a battery. State what happens to the other lamp if one is removed.[1]
4. (d)Give one reason houses wire lamps in parallel rather than in series.[1]

A car headlamp is labelled 12 V, 36 W.

1. (a)Calculate the lamp's normal operating current.[2]
2. (b)Calculate the lamp's resistance at normal brightness.[2]
3. (c)Explain why its cold resistance is much lower.[1]

This question is about the three I–V characteristics.

1. (a)Sketch (or describe) the I–V graph of a fixed resistor at constant temperature.[1]
2. (b)Describe the I–V graph of a filament lamp and explain its shape.[3]
3. (c)State the forward turn-on voltage of a typical silicon diode.[1]

A greenhouse uses an NTC thermistor to control a heater: when the thermistor is cold, the heater must switch on.

1. (a)State what happens to the thermistor's resistance as the greenhouse cools.[1]
2. (b)Explain how the circuit can use this to switch the heater on.[2]
3. (c)An LDR is used for an automatic light. State what happens to the LDR's resistance at dusk and what the circuit does.[2]

A student measures a wire's resistance at different lengths: 0.30 m gives 1.8 Ω.

1. (a)Predict the resistance at 0.60 m, with a reason.[2]
2. (b)Describe how the student should measure the resistance of each length.[2]
3. (c)State one variable that must be controlled.[1]

This question is about tracing a component's I–V curve in the lab.

1. (a)Draw (or describe) the circuit used to obtain a component's I–V characteristic.[3]
2. (b)Explain the role of the variable resistor and why readings are also taken with reversed connections.[2]
3. (c)State one precaution that keeps the fixed resistor's temperature constant.[1]

(Higher) A 12 V battery drives a circuit in which two 6 Ω resistors are connected in parallel, and the pair is in series with a 3 Ω resistor.

1. (a)Calculate the resistance of the parallel pair.[1]
2. (b)Calculate the total resistance and the supply current.[2]
3. (c)Calculate the p.d. across the parallel pair and the current in each 6 Ω branch.[3]

(Higher) Explain, using the model of electrons and ions, the effect of length and cross-sectional area on a wire's resistance.

1. (a)Explain why resistance increases with length.[3]
2. (b)Explain why resistance decreases with cross-sectional area.[3]

A 6.0 V supply is connected across a lamp. An ammeter reads 0.30 A.

1. (a)Calculate the lamp's resistance at this brightness.[2]
2. (b)The supply is raised to 12 V but the current only rises to 0.45 A. Explain what this shows about the lamp.[2]