The back e.m.f. induced in a coil, when current changes from 1 ampere to zero in one milli‑second, is 4 volts, the self inductance of the coil is
|
(a) 1 H |
(b) 4 H |
(c) |
(d) 4 |
(d) 4 
H
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Three equal resistors connected in series across a source of e.m.f. together dissipate 10 watt. If the same resistors are connected in parallel across the same e.m.f., then the power dissipated will be
|
(a) 10 watt |
(b) 30 watt |
(c) 10/3 watt |
(d) 90 watt |
A double convex lens of glass of m = 1.5 has radius of curvature of each of its surface is 0.2 m. The power of the lens is
|
(a) + 10 dioptres |
(b) – 10 dioptres |
(c) – 5 dioptres |
(d) +5 dioptres |
amp is flowing through a resistance of 1000Ω. To measure the correct potential difference, the voltmeter is to be used of which the resistance should be
|
(a) 0 Ω |
(b) 500 Ω |
(c) 1000 Ω |
(d) >> 1000 Ω |
A current of 2 A passing through conductor produces 80 J of heat in 10 seconds. The resistance of the conductor is
|
(a) 0.5 Ω |
(b) 2 Ω |
(c) 4 Ω |
(d) 20 Ω |
The activity of a radioactive sample is measured as 9750 counts per minute at t = 0 and as 975 counts per minute at t = 5 minutes. The decay constant is approximately
|
(a) 0.230 per minute |
(b) 0.461 per minute |
|
(c) 0.691 per minute |
(d) 0.922 per minute |
