1. Wire A, which is of the same length and material as wire B, has three time di
ID: 306408 • Letter: 1
Question
1. Wire A, which is of the same length and material as wire B, has three time diameter larger than wire B. If the resistance of wire B is R, what is the resistance of wire A? A) R B) 3R E) R/3 R. 2. A resistor develops heat at the rate of 30 W when the potential difference across its ends is 30 V. The resistance of the resistor is approximately A) 45 ? B) 5.5 ? C) 30 ? D) 10? 900 ? 3. The current in a wire varies with time according to the relation 1-5+92 where / is in amperes and t is in seconds. The number of coulombs of charge that p cross section of the wire between- 3s and-5 s is A) 14 B) 304 C) 346 106 E) 230 . A wire of length L and resistance R is cut into 4 equal pieces. If the 4 pieces ar twisted together to make a wire of length L/4, what is the new resistance of the wire combination A) R/16 B) R/4 C) R D) 4R (E 16RExplanation / Answer
1.As we know,
R= rho*L/A
For same length and same meterial,
R is inversely proportupropto r^2
R2= R*(r1/r2)^2= R*(3r/r)^2
R2= 9R
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2.
P=v^2/R
R= 30*30/30= 30 ohm
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3.
Charge,
Q= integration (limit 3-5) i. dt
= [ 5t+ 3*t^3) from 3-5
= 5*(5-3)+3*(5^3-3^3)
= 10+3*98
= 304 C
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4.
New resistance of each wire,
R'= R/4
net resistance in parallel combination
1/Rnet= 4*(1/R')
Rnet= R/16
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Comment in case any doubt..goodluck
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