Circuits – MCQs (set 6) Internal resistance

A cell C of negligible resistance and a switch are in series with a resistor R. The switch is moved to the on (closed) position for a time t. Which change reduces the amount of charge flowing through R in time t?

• add an identical cell in parallel with C

• add an identical cell in series with C

• add a second resistor in series with R

• add a second resistor in parallel with R

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

Three identical cells, each of internal resistance R, are connected in series with an external resistor of resistance R. The current in the external resistor is I. If one of the cells is reversed in the circuit, what is the new current in the external resistor?

• I / 3

• 4I / 9

• I / 2

• 2I / 3

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?

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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.

In the circuit shown in the diagram the cell has negligible internal resistance. What happens to the reading of both meters when the resistance of R is decreased?

• Reading of ammeter increases, Reading of voltmeter increases.

• Reading of ammeter increases, Reading of voltmeter decreases.

• Reading of ammeter decreases, Reading of voltmeter increases.

• Reading of ammeter unchanged, Reading of voltmeter decreases.

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 EMF of the cell

• The power dissipated by the cell

• The resistance of the variable resistor

The diagram shows a network of resistors connected between the terminals P and Q. The resistance of each resistor is shown. What is the effective resistance between P and Q?

• R

• 2R

• 3R

• 4R

A potential divider circuit consists of a battery connected across a thermistor and variable resistor in series. Which of the following causes the potential difference (PD) across the thermistor to increase?

• increasing the temperature of the thermistor

• increasing the resistance of the variable resistor

• reducing the EMF of the battery

• adding a resistor across the variable resistor