Answer the following questions based on the circuit in Fig. 8. When switches S_1

Question

Answer the following questions based on the circuit in Fig. 8. When switches S_1 and S_2are open, the ammeter reading is 0.6 A and voltmeter reading is 2.4 V calculate: the resistance of the lamp; the resistance of R_1. Compare the brightness of the lamp when both switches are open as in (a) and when only switch S_1 is closed. Give a quantitative explanation. Compare the brightness of the lamp when both switches are open as in (a) and when both switches S_1 and S_2 are closed. Give a quantitative explanation. For R_2 = 4 ohm, if switch S_1 is opened but switch S_2 is closed, what is ammeter reading? What is voltmeter reading?

Explanation / Answer

a) resistance of the lamp, R_lamp = V/I

= 2.4/0.6

= 4 ohms

V_battery = I*(R_lamp + R1)

6 = 0.6*(4 + R1)

10 = 4 + R1

==> R1 = 10 - 4

= 6 ohms

b) when S1 is closed. Current through the bulb increases. so, the brightness increases.

When s1 is closed current through the bulb, I = V_battery/R_lamp

= 6/4

= 1.5 A

c) when S1 and S2 are closed. Current through the bulb increases. so, the brightness increases.

When s1 and S2 are closed current through the bulb, I = V_battery/R_lamp

= 6/4

= 1.5 A

d) Rnet = R1 + R2*R_lamp/(R2 + R_lamp)

= 6 + 4*4/(4+4)

= 8 ohms

Ammeter reading, I = V_battery/Rnet

= 6/8

= 0.75 A

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