Circuits and EMF

A cell of emf ε and internal resistance r delivers current to a small electric motor.

450 C of charge flows through the motor and 9000 J of energy are converted in the motor. 1800 J are dissipated in the cell. The emf of the cell is

• 4.0 V

• 16 V

• 20 V

• 24 V

The electromotive force (emf) of a cell is defined as

• the power supplied by the cell per unit current from the cell.

• the force that the cell provides to drive electrons round a circuit.

• the energy supplied by the cell per unit current from the cell.

• the potential difference across the terminals of the cell.

In the circuits below the cells have the same emf and zero internal resistance. The resistors all have the same resistance.

Which of the following gives the ratio

power dissipated in X / power dissipated in Y ?

• 1/4

• 1/2

• 2

• 4

A battery of internal resistance 2 Ω is connected to an external resistance of 10 Ω. The current is 0.5 A.

What is the emf of the battery?

• 1.0 V

• 5.0 V

• 6.0 V

• 24.0 V

A resistor has a resistance R. The potential difference across the resistor is V. Which of the following gives the energy dissipated in the resistor in time t?

• Vt/R

• Rt/V²

• RV²t

• V²t/R

A cell has an emf of 4.0 V and an internal resistance of 2.0 Ω. The ideal voltmeter reads 3.2 V.

What is the resistance of R?

• 0.8 Ω

• 2.0 Ω

• 4.0 Ω

• 8.0 Ω

The diagram shows a circuit used to investigate internal resistance of a cell.

The variable resistor R is adjusted and the values of potential difference V across the cell and current I are recorded. Which graph shows the variation of V with I?

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