Specimen and sample questions - Electricity

1. The p.d. across a resistor is 12 V. The power dissipated is 6.0 W. Which statement is correct?

• A. The charge passing through the resistor in one second is 2.0 coulomb.

• B. The resistor transfers 6.0 joule for each coulomb passing through the resistor.

• C. The resistor transfers 12 joule in 2.0 second.

• D. The resistor dissipates 6.0 joule when the current is 2.0 ampere.

The diagram below shows a cell with an internal resistance connected to an external resistor. Which of the following will increase the terminal p.d? 1. Increasing the e.m.f. of the cell. 2. Increasing the value of the external resistance. 3. Increasing the value of the internal resistance.

• 1, 2 and 3

• Only 1 and 2

• Only 2 and 3

• Only 1

A battery of e.m.f. of 8.0 V and internal resistance 2.5 Ω is connected to an external resistor. The current in the resistor is 350 mA. What is the power dissipated in the external resistor?

• 1.9 W

• 2.5 W

• 2.8 W

• 3.1 W

A resistor is connected across a power supply. Which statement is correct about the conduction electrons in this resistor?

• They travel at the speed of light between collisions with ions.

• They make random collisions with vibrating electrons.

• They travel at their mean drift velocity between collisions.

• They drift towards the positive end of the power supply.

Calculate the ratio of current from battery in circuit of Fig. 24.1 to current from battery in circuit of Fig. 24.2.

• 1:1

• 2:1

• 1:2

• 3:1

The graph shows the I-V characteristic of a semiconductor diode. Which statement about the resistance of the diode can be deduced from the characteristic?

• It is zero between 0 V and 0.70 V.

• It is constant between 1.0 V and 1.5 V.

• It is 0.4 Ω at 1.2 V.

• It decreases between 0.70 V and 1.0 V.

7. 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. resistance = ........................................ Ω

• 1.6 x 10^-7 Ωm

• 2.4 x 10^{-7} Ωm

• 3.2 x 10^{-7} Ωm

• 4.0 x 10^{-7} Ωm

The voltmeter used in the experiment had a zero error. The potential difference recorded in the experiment was smaller than it should have been. How would the actual value of the resistivity of the metal differ from the value calculated?

• The actual resistivity would be higher than calculated.

• The actual resistivity would be lower than calculated.

• The actual resistivity would be the same as calculated.

• The actual resistivity cannot be determined.

9. *In order to determine the I-V characteristic for an LED, one student connects to the incomplete circuit X shown in Fig. 4.2(a) and a second student connects to the incomplete circuit Y shown in Fig. 4.2(b). Each adds an LED with a resistor in series and suitable meters to take the measurements between terminals A and B. Only one of these circuits is suitable to carry out the task. Which circuit is suitable to carry out the task and why has the 100 Ω resistor been included?

• Circuit X is suitable because it allows for proper current flow and the 100 Ω resistor limits the current to prevent damage to the LED.

• Circuit Y is suitable because it allows for proper current flow and the 100 Ω resistor limits the current to prevent damage to the LED.

• Circuit X is suitable because it provides a parallel connection which is necessary for the task, and the 100 Ω resistor is included to adjust voltage.

• Circuit Y is suitable because it provides a parallel connection which is necessary for the task, and the 100 Ω resistor is included to adjust voltage.