A 1.2 m long metal wire has a radius of 1.3 cm and a resistance of 3.1 times 10^
ID: 1647033 • Letter: A
Question
A 1.2 m long metal wire has a radius of 1.3 cm and a resistance of 3.1 times 10^-5 Ohm. What is the resistivity of the metal? 4.68 times 10^-8 Ohm-m 0.812 times 10^-8 Ohm-m 11.16 times 10^-8 Ohm-m 5.03 times 10^-8 Ohm-m 3.72 times 10^-8 Ohm-m A 3 ohm, 20 mA galvanometer is converted into an ammeter by placing a 7.4 times 10^-2 Ohm shunt in parallel with the galvanometer coil. The maximum scale reading on the galvanometer is: 0.8108 A 2.886 A 1. 8A 2.7A 0.444 A A series RC circuit has a time constant of 3.8 s. The battery has a voltage of 32 V and the maximum current just after closing the switch is 19 A. The capacitor is initially uncharged. What is the charge on the capacitor 4.6 s after the switch is closed? 52.44 mu C 2.64 mu C 36.48 mu C 25.34 mu C 17.48 mu CExplanation / Answer
(7) We know that the resistance (R) = pL/A
where p is its resistivity , L is the length and A is its area
L = 1.2 m , A = Pi*r2 = Pi*(1.3*10-2)2 = 5.309*10-4 m2
R = 3.1*10-5 ohm
Putting all the values in the above relation
3.1*10-5 = p*(1.2) /(5.309*10-4 )
p = 1.371*10-8 ohm -m
Since the option is not available therefore we will mark the closest option that is B.
(8) We know that the
shunt is given by
S = Ig*G / I - Ig
where G = 3 ohm is the galvanometer resistance and Ig is the full current deflection = 20*10-3 A,
I will be the maximum current of the ammeter
7.4*10-2 = 20*10-3*3 / (I - 20*10-3)
I = 0.8308 A
hence the correct option would be A.
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