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**The identical cells connected in series are needed to heat a wire of length one meter and radius ‘r’ by 10⁰C in time ‘t’. How many cells will be required to heat the wire of length two meter of the same radius by the same temperature in time ‘t’? **

### Options

(a) 10

(b) 20

(c) 30

(d) 40

### Correct Answer:

20

### Explanation:

Resistance is directly proportional to length of the wire. As length is doubled so mass is doubled and resistance is doubled. We have

(10 E)² / R . t = mS∆T,

Now, (nE)²t / 2R = (2m) S∆T

⇒ n²E²t / 2R = 2 . 10²E²t / R

⇒ n = 20

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Topics: Current Electricity
(136)

Subject: Physics
(2479)

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