Multiple Choice--I\'m not sure of the reasoning. We didn\'t learn this in class

Question

Multiple Choice--I'm not sure of the reasoning. We didn't learn this in class yet.

1. A circuit consists of a 12 V battery connected to a switch, which is connected to a light bulb of resistance 120 O and then back to the battery. If the switch is open, which statement is true of I (the current through the switch and Vs (the difference in potential across the poles of the switch)?

I = 10 A, Vs is not zero but less than 12 V
I = 0.1 A, Vs is more than 12 V
I = 10 A, Vs = 12 V
I = 0 A, Vs is not zero but less than 12 V
I = 0 A, Vs = 12 V
I = 0.1 A, Vs = 12 V
I = 0.1 A, Vs = 0 V
I = 0.1 A, Vs is not zero but less than 12 V
I = 10 A, Vs = 0 V
I = 0 A, Vs is more than 12 V
I = 0 A, Vs = 0 V
I = 10 A, Vs is more than 12 V

Explanation / Answer

I = 0 A, Vs = 12 V

When the switch is open, it offers infinite resistance

current through the circuit I = V / R

= 12 / (120 + )

= 0 A

Voltage across the switch = battery EMF - voltage drop across the bulb

VS   = 12 - 0 * 120

= 12 V

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