Topic 2.5: Current and Circuits Questions

A length of constantan wire has a resistance of 6.0 Ω.

A second wire of the same material and the same cross-sectional area has three times the length of the first.

Deduce the resistance of the second wire.

State what is meant by the resistance of an electrical component.

Two resistors, 5.0 Ω and 15 Ω, are connected in series with a cell of negligible internal resistance.

The current in the circuit is 0.40 A.

Determine the emf of the cell.

A cell of emf 4.5 V and internal resistance 1.2 Ω is connected to a single resistor of resistance 7.8 Ω.

Calculate the current in the circuit.

State what is meant by the emf of a cell.

Define potential difference between two points in a circuit.

An electric kettle is labelled 2300 W when connected to the 230 V mains supply.

(a) Calculate the current drawn by the kettle.

(b) Calculate the resistance of its heating element at this operating temperature.

A cell is connected to a fixed external resistor.

Outline why the terminal potential difference of the cell is smaller than its emf when current flows.

State what is meant by an electric current of 1 ampere.

A torch bulb carries a steady current of 0.25 A.

Determine the charge that flows through the bulb in 1.0 minute.

A potential difference of 12 V is applied across a fixed resistor and a current of 2.5 A flows through it.

Determine the resistance of the resistor.

A phone charger delivers a steady 5.0 W to a phone while charging it.

The phone takes 2.5 hours to charge fully.

Estimate the electrical energy delivered to the phone during one full charge, giving your answer in joules.

Identify whether the current or the potential difference is the same for two resistors connected in parallel, and state which resistor — the larger or the smaller — carries the greater current.

A heating element of fixed resistance is run from a supply whose voltage can be adjusted.

The voltage across the element is reduced to half its original value.

State and explain what happens to the power dissipated by the element.

A 9.0 V battery drives a current of 0.50 A through a small motor for 2.0 minutes.

Calculate the total charge that passes through the motor, and the total electrical energy the battery gives to that charge.

In a network, a 3.0 Ω resistor is connected in series with a parallel combination of a 6.0 Ω resistor and a 12 Ω resistor.

Calculate the equivalent resistance of the whole network.

A 12 V car battery transfers 2.4 kJ of electrical energy to charge passing through a heating element.

Calculate the charge that flows through the element.

The current–voltage (I–V) graph of a metal resistor S is a straight line through the origin.

At a voltage of 4.0 V the current is 0.50 A; at 8.0 V the current is 1.0 A.

Calculate the resistance of S, and explain how the shape of the graph confirms that S is ohmic.

Two resistors, 12 Ω and 4.0 Ω, are connected in parallel and the combination is placed across a 12 V supply.

Calculate the equivalent resistance of the pair, then determine the current in each branch and the total current drawn from the supply.

A cylindrical carbon rod has length 0.080 m and diameter 4.0 mm.

The resistivity of the carbon is 3.5 × 10⁻⁵ Ω m.

Calculate the resistance between the flat ends of the rod.