P.3.5.1.6 Electromotive force; internal resistance

The reading on the voltmeter halves when switch S is closed.

What is the internal resistance of the cell?

• 0.50 Ω

• 1.0 Ω

• 2.0 Ω

• 4.0 Ω

Three cells each have an emf ε = 1.5 V and an internal resistance r = 0.6 Ω.

Which combination of these cells will deliver a total emf of 1.5 V and a maximum current of 7.5 A?

• A

• B

• C

• D

The cell in the following circuit has an emf (electromotive force) of 6.0 V and an internal resistance of 3.0 Ω. The resistance of the variable resistor is set to 12 Ω.

How much electrical energy is converted into thermal energy within the cell in 1 minute?

• 0.48 J

• 29 J

• 45 J

• 144 J

The cell in the circuit has an emf of 2.0 V. When the variable resistor has a resistance of 4.0 Ω, the potential difference (pd) across the terminals of the cell is 1.0 V.

What is the pd across the terminals of the cell when the resistance of the variable resistor is 12 Ω?

• 0.25 V

• 0.75 V

• 1.33 V

• 1.50 V

In the circuit shown, V is a voltmeter with a very high resistance. The internal resistance of the cell, r, is equal to the external resistance in the circuit.

Which of the following is not equal to the emf of the cell?

• the reading of the voltmeter when the Switch S is open

• the chemical energy changed to electrical energy when unit charge passes through the cell

• twice the reading of the voltmeter when the switch S is closed

• the electrical energy produced when unit current passes through the cell

A student investigates how the potential difference V across the terminals of a cell varies with the current I in the cell.

Which graph correctly shows how V varies with I?

• A

• B

• C

• D

A battery is connected to a 10 Ω resistor and a switch in series. A voltmeter is connected across the battery. When the switch is open (off) the voltmeter reads 1.45 V. When the switch is closed the reading is 1.26 V.

What is the internal resistance of the battery?

• 0.66 Ω

• 0.76 Ω

• 1.3 Ω

• 1.5 Ω

The circuit in Figure 1 is used to investigate how the potential difference V between the terminals of a cell varies as the current I in the circuit changes. Figure 2 shows the graph of the results.

Which one of the following can be deduced from the gradient of the graph?

• The internal resistance of the cell

• The e.m.f. of the cell

• The power dissipated by the cell

• The resistance of the variable resistor