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A three - way light bulb has three brigh...

A three - way light bulb has three brightness settings ( low , medium , and high) but only two filaments . The two filaments are arranged in three settings, when connected across a `120 V` line and can dissipate `60 , 120 and 180 W`. Answer the following questions:

A

all three settings is `120 W`

B

all three settings is `60 W`

C

two settings is `60 W`

D

two settings is `120 W`

Text Solution

Verified by Experts

The correct Answer is:
D
The `60 W` bulb will be of higher resistance. If only switch `1` is closed , `120 W` bulb will glow. If only switch `2` is closed , `60 W` bulb will glow . If both the switches are closed, both bulbs will glow with total illumination of `180 W`.
When the filament of higher resistance ( of `60 W` bulb) burns out, then for two settings ( either `1` is closed or both are closed) power dissipated will be `120 W`.
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