D. C. circuits

A student varies the variable resistor R and measures the current I and potential difference V. He plots a graph of V against I. Which is the correct answer?

• gradient = e.m.f.; y-intercept = internal resistance

• gradient =internal resistance; y-intercept = e.m.f.

• gradient = internal resistance; y-intercept = 1/e.m.f.

• gradient = 1/ e.m.f.; y-intercept = internal resistance

What is meant by the electromotive force (e.m.f.) of a cell?

• the e.m.f. of a cell is the energy converted into electrical energy when unit charge passes through the cell.

• the e.m.f. of a cell is the energy transferred by the cell in driving unit charge through the external resistance.

• the e.m.f. of a cell is the energy transferred by the cell in driving unit charge through the internal resistance of the cell.

• the e.m.f. of a cell is the amount of energy needed to bring a unit positive charge from infinity to its positive pole

The value of the external resistance R is slowly increased from zero. Which statement is correct? (Ignore any temperature effects.)

• A potential difference across the external resistance decreases.

• A potential difference across the internal resistance increases.

• The power dissipated in r increases and then decreases.

• The power dissipated in R increases and then decreases.

A high-resistance voltmeter connected across a battery reads 6.0 V. When the battery is connected in series with a lamp of resistance of 10 W, the voltmeter reading falls to 5.6 V. Which statement explains the observation?

• The electromotive force (e.m.f.) of the battery decreases because more work is done across its internal resistance.

• The e.m.f. of the battery decreases because work is done across the lamp.

• The potential difference (p.d.) across the battery decreases because more work is done across it internal resistance.

• The p.d. across the battery decreases because work is done across the lamp.

A source of e.m.f. of 9.0 mV has an internal resistance of 6.0 Ω . It is connected across a galvanometer of resistance 30 Ω. What will be the current in the galvanometer?

• 250 μA

• 300 μA

• 1.5 mA

• 2.5 mA

A power supply of electromotive force (e.m.f.) 12 V and internal resistance 2.0 Ω is connected in series with a load resistor. The value of the load resistor is varied from 0.5 Ω to 4 Ω. Which graph shows how the power P dissipated in the load resistor varies with the resistance of the load resistor?

• A

• B

• C

• D

The sum of the electrical currents into a point in a circuit is equal to the sum of the currents out of the point. Which of the following is correct?

• This is Kirchhoff’s first law, which results from conservation of charge.

• This is Kirchhoff’s first law, which results from conservation of energy.

• This is Kirchhoff’s second law, which results from conservation of charge.

• This is Kirchhoff’s second law, which results from conservation of energy.

Which of the following is not true for resistors in series?

• the sum of p.d. across all the resistors equal to the source of e.m.f. of negligible internal resistance

• the current through each resistor is the same.

• the combined resistance is always greater than any individual resistance.

• the p.d. across each resistor is the same.

Which of the following is incorrect for resistor in parallel?

• the sum of p.d. across all the resistors equal to the source of e.m.f. of negligible internal resistance

• the sum of current through each resistor is equal to the current supplied.

• the combined resistance is always less than any individual resistance.

• the p.d. across each resistor is the same.

The current in the external resistor is 0.50 A. What is the internal resistance r of each battery?

• 1.0 Ω

• 2.0 Ω

• 4.0 Ω

• 6.5 Ω