A battery is used to light a bulb as shown. A second bulb is connected by closin

Question

A battery is used to light a bulb as shown. A second bulb is connected by closing switch S. What happens to the bulbs? A) The right bulb goes out; the left bulb lights up. B) The right bulb gets noticeably dimmer; both bulbs have the same brightness. C) The right bulb gets very slightly dimmer; both bulbs have the same brightness. D) The right bulb's brightness stays the same; both bulbs have the same brightness. E) The right bulb gets slightly brighter; both bulbs have the same brightness. A battery is used to light two bulbs as shown. What happens to bulb B when bulb A is unscrewed from its socket? A) Bulb B goes out. B) Bulb B gets noticeably dimmer, without going out. C) Bulb B gets slightly dimmer. D) Bulb B gets slightly brighter. E) Bulb B's brightness stays the same.

Explanation / Answer

1) Ans: (D) The right bulb’s brightness stays the same; both bulbs have the same brightness.

Let the resistance of the bulbs be 1 ohm and the battery voltage be 1V.

Initial condition:

Current I = V/R = 1A

This passes through the 1st bulb.

Final condition:

Now equivalent R = 1 parallel 1 = 0.5 ohm

Therefore I = 1/0.5 = 2 A

This gets equally divided between the two bulbs; i.e. 1A each.

Thus the brightness remains same and is equal.

2) Ans: (E) Bulb B’s brightness stays the same.

Same reasoning.

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