CBSE Class 10 Answered
A piece of wire of resistence 20 ohm drawn out to increase its length to twice as original length .calculate its resistence now.
Asked by Selvadhaya | 30 Mar, 2020, 13:55: PM
When the length of the wire is doubled the area of cross section is reduced to half and resistance becomes four times the original value.
Thus,
Initial resistance R is 20 Ω for length L and area of cross section is A
We know,
R = ρL/A ... (1)
When length is doubled L = 2L area of cross section becomes A =A/2
The new resistance becomes
R' = ρ(2L)/(A/2) .... (2) (resistivity 'ρ' is same for given substance)
= 4(ρL/A)
Thus,
R' = 4R ... (from (1) and (2))
R' = 4 × 20 = 80 Ω
Answered by Shiwani Sawant | 30 Mar, 2020, 14:11: PM
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