Electricity A Level summary

A battery charger contains a microprocessor circuit so that it can charge an AA rechargeable cell at a constant current of 450 mA. It takes 4 hours 40 minutes to charge a 1.5 V cell from a fully discharged state.

Calculate the charge Q passing through the cell during the charging process. (2 sig fig with units)

A battery of negligible internal resistance is connected across two resistors of resistance values R and 2R as shown in Fig. 24.1.

The same battery is now connected to the same resistors as shown in Fig. 24.2.

Calculate the ratio between the currents of the 2 circuits: = current from battery in circuit 24.1 / current from battery in circuit 24.2

(answer to 2 sig fig, no unit)

Two batteries, each of e.m.f 6.0 V and negligible internal resistance, are joined in parallel. The cells are connected to two identical resistors, joined in parallel.

What is the voltage across each resistor?

• 1.5 V

• 3.0 V

• 6.0 V

• 12.0 V

The circuit in Fig. 2.1 consists of a cell and five resistors.

Calculate the p.d. across the 6.0 Ω resistor. The current at point X is 0.16 A.

(2 sig fig + unit symbol)

The circuit in Fig. 2.1 consists of a cell and five resistors.

Calculate the value of the internal resistance r. The current at point X is 0.16 A.

(2 sig fig, no unit needed)

Two filament lamps X and Y are connected in parallel to a supply.

The power dissipated by lamp X is 24 W and the power dissipated by lamp Y is 6.0 W.

The supply has electromotive force (e.m.f.) 12 V and negligible internal resistance.

What is the total current drawn from the supply by the lamps?

• 0.4 A

• 0.5 A

• 2.0 A

• 2.5 A

Fig. 24.2 shows a circuit designed by a student.

The cell has e.m.f. 1.5 V and an internal resistance r.

The uniform wire AB has length 1.0 m and resistance 16 Ω.

When the contact X is in the middle of the wire, the voltmeter reading is 1.2 V.

Calculate the internal resistance r of the cell in ohms. (2 sig fig, no units)

The circuit in Fig. 5.1 consists of a d.c. supply of e.m.f. 45 V and negligible internal resistance and three resistors.

Two of the resistors have resistances 1000 Ω and 750 Ω as shown.

The current drawn from the supply is 0.030 A. Calculate the resistance of R. (2 sig fig, no unit needed)

A 14 V d.c. supply is used to charge a 12 V car battery of internal resistance 0.80 Ω for 6.0 hours. The current in the circuit is 2.5 A.

How much electrical energy is provided by the charging supply?

• 13 kJ

• 110 kJ

• 650 kJ

• 760 kJ

What current would flow?

• 0.36 A

• 1.04 A

• 0.021 A

• 0.82 A