# Form 3 Physics Current Electricity II Questions and Answers

In this course, we are going to solve several form 3 Physics questions on current electricity II. Answers are available in video format.

Lessons (**35**) * SHARE*

- 1.
Study the circuit diagram in figure 1 and answer the following questions.
(a) Calculate the effective resistance between Y and Z.
(b) Determine the current through the 3#Omega# resistor. (c) One of the 6#Omega# resistors has a length of 1.0m and cross-section area of 5.0 x #10^-6 m^2#. Calculate the resistivity of the material.

8m 51s - 2.
A thermistor, TH, is connected in parallel with a bulb as shown in Fig. 3. The bulb is lit. When the thermistor is steadily heated, the brightness of the bulb reduces. Explain this observation.

3m 50s - 3.
In large current circuits, large resistors in parallel are preferred to low resistors in series. Explain.

3m 29s - 4.
The diagram in Fig. 2 represents an electric circuit in which five resistors are connected to be a battery of e.m.f. 4.0 V and of negligible internal resistance.
Determine:
(i) The total resistance of the circuit. (ii) The current flowing through the 5.5#Omega# resistor. (iii) The potentials at points Y and Q. (iv) The potential difference between Y and Q.

10m 2s - 5.
Use the information in fig. 8 to answer questions 5 and 6. What is the p.d across YZ when the switch S is open?

0m 55s - 6.
Determine the p.d. across YZ when the switch S is closed.

4m 3s - 7.
The internal resistance of the cell E, in Fig. 3 is 0.5 ohms. Determine the ammeter reading when the switch, S, is closed.

2m 23s - 8.
State the reason why a voltmeter of high resistance is more accurate in measuring potential differences, than one of low resistance.

3m 26s - 9.
Calculate the length of a wire required to make a resistor of 0.5 ohms, if the resistivity of the material is 4.9 x #10^-7 Omega# m and the crosssectional area is 2.0 x #10^-6 m^2#.

3m 20s - 10.
Determine the ammeter reading when a p.d. of 3.0 volts is applied across PQ in figure 8.

2m 34s - 11.
A circuit consists of a battery, a metal wire, an ammeter and a switch connected in series. The switch is closed and the ammeter reading noted. The metal wire is now heated. State the observations made on the ammeter reading and give a reason for your answer.

5m 0s - 12.
The ammeter in the circuit in figure 11 has negligible resistance. When the switch S is closed, the ammeter reads 0.10A. Determine the internal resistance of the battery.

2m 6s - 13.
A current of 0.70A flows through a wire when a p.d. of 0.35V is applied at the end of the wire. If the wire is 0.5m long and has across section area of 8.0 x #10^-3 m^2#, determine its resistivity.

3m 29s - 14.
Figure 4 shows an electrical circuit. When the switch is closed, the ammeter reading is 0.3A. Determine the voltmeter reading.

1m 24s - 15.
(a) State what is meant by electromotive force (e.m.f.) force of battery (b) The graph in figure 5 shows how the terminal voltage, V, of a certain battery varies with the current, I, being drawn from the battery. (i) Sketch the circuit that could be used
to obtain the plotted results. (ii) Write an expression relating the e.m.f., E, terminal voltage, V, current, I and the internal resistance, r,

11m 8s - 16.
A student wishes to investigate the relationship between current and voltage for certain device X. in the space provided, draw a circuit diagram including two cells, rheostat, ammeter, voltmeter and the device X that would be suitable in obtaining the desired results.

2m 46s - 17.
The graph below shows the voltage-current relationship for a certain conductor.
(i) Determine the resistance of the conductor.
(ii) Given that the length of the conductor used was 0.50 m and the radius of its crosssection was 0.4mm, determine the resistivity, p, of the material of the conductor.

4m 5s - 18.
State one condition under which Ohm’s law is obeyed in a metal conductor.

1m 10s - 19.
In the circuit diagram shown in figure 7, the ammeter has negligible resistance. When the switch S, is closed, the ammeter reads 0.13A.
Determine the internal resistance of the cell.

2m 21s - 20.
A heater of resistance R1 is rated P watts, V volts while another of resistance #R_2# is rated 2p watts, v/2 volts. Determine #R_1/R_2#.

2m 51s - 21.
(a) State Ohm’s law. (b) The graph in figure 9 shows the current – voltage characteristics of a certain device, X. (i) State with a reason whether the device obeys Ohm’s law. (ii) Determine the resistance of the device, X, when the
current through it is 60 mA.
(iii) When the device, X is connected in the circuit below, the voltage across it is 0.70 V.
Calculate the value of the resistance

0m 0s - 22.
You are provided with the following: A cell and a holder, a switch, a rheostat, an ammeter, a voltmeter and connecting wires. Draw a diagram for a circuit that can be used to investigate the variation of the potential difference across the cell with the current drawn from the cell

2m 18s - 23.
Figure 6 shows a circuit in which a battery of negligible internal resistance, two resistors, a capacitor, a voltmeter and a switch are connected.
Giving a reason for your answer in each case, state the reading of the voltmeter, V, when the switch is (i) Open (ii) Closed.

3m 8s - 24.
(a) Three resistors of resistance 2.0#Omega#, 4.0#Omega# and 6.0#Omega# are connected together in a circuit. Draw a circuit diagram to show the arrangement of the resistor which gives (i) Effective resistance of 3.0#Omega#
(ii) Minimum resistance. (b) In figure 11, the voltmeter reads 2.1 V when the switch is open. When the switch is closed, the voltmeter reads 1.8 V and the ammeter reads 0.1A.

0m 0s - 25.
Figure 3 shows part of an electrical circuit. The current through the 18 Ohms resistor is observed to be 2A. State the value of the current through each of the 10 Ohms resistors

1m 20s - 26.
Figure 9 shows the graph of the relationship between current I and potential difference V and lamp Y are 2.5 V and 3.0 V respectively. (a) Explain the change in the shape of the curves as the current increases. (b) Determine the resistance of lamp X at
the normal working voltage. (c) The lamps are now connected in a series circuit in which a current of 0.4 A flows. Find the potential differences

6m 43s - 27.
(a) Figure 13, shows a cell in series with a 3 Ohms resistor and a switch. A high resistance voltmeter is connected across the cell. The voltmeter reads 1.5V with the switch open and 1.2V with the switch closed.
(i) State the electromotive force of the cell. (ii) Determine the current through the 3 Ohms resistor when
the switch is closed. (iii) Determine the internal resistance of the cell.

5m 47s - 28.
(a) Figure 8 shows a graph of potential difference V (volts) against a current, I (amperes) for a certain device. From the graph:
(i) State with a reason whether or not the device obeys Ohm’s law (ii) Determine the resistance of the device at;
(I) I = 1.5 A (II) I = 3.5 A (iii) From the results obtained in (ii), state how the resistance of the device varies the current increases. (iv) State

14m 46s - 29.
Figure 3 shows four identical light bulbs connected to a 15 volt battery whose internal resistance is negligible. Determine the reading of the voltmeter V.

2m 7s - 30.
Figure 14 shows a circuit in which a battery, a switch, a bulb, a resistor P, a variable resistor C, a voltmeter V and two ammeters A and A of negligible resistance are connected. P has resistance of 10 Ohms. When the switch is closed, A reads 1.5 V.
(a) Determine: (i) The current passing through P (ii) The resistance of the bulb

4m 10s - 31.
Figure 1 shows a cell of e.m.f 2V connected in series with a resistor R and a switch S. voltmeter #V_1# and #V_2# are connected across the cell and the resistor respectively. (a) State the reading of #V_1# with S open. (b) With S closed, #V1# reads 1.6V. State the reading of #V_2#.

0m 58s - 32.
Figure 7 shows resistors #R_1# and #R_2# connected in parallel. Their ends are connected to a battery of potential difference V volts.
(i) In terms of #V_1#, #R_1#, and #R_2#, write an expression for (I) Current #I_1# through #R_1#.
(II) Current #I_2# through #R_2#. (III) Total current I in the circuit. (ii) Show that the total resistance #R_T# is given by #R_T = (R_1R_2)/(R_1 + R_2#

6m 17s - 33.
Three resistors of resistance 2 Ohms, 3 Ohms and 4 Ohms are to be connected to a cell such that they have the least effective resistance. (i) Draw a circuit diagram to show how they can be connected to achieve this. (ii) Determine the least effective resistance of the three resistors.

3m 52s - 34.
Figure 4 shows three resistors connected in series. Using Ohm's law, show that the effective resistance is given by the expression: RT = R1 + R2 + R3.

2m 39s - 35.
Figure 3 shows a cell connected in series with an ammeter, a 2 Ohm resistor a switch. A voltmeter is connected across the cell.
With the switch open, the voltmeter reads 1.5 V. Given that the internal resistance of the cell is 5 Ohms, determine the ammeter reading when the switch is closed.

2m 6s

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