UPSC SCRA Question Papers
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SCRA-UPSC-Physical Science-2011 solved question papers
1. Two a-particles, each of 13.2 MeV energy are produced when a 3Li6 nucleus is bombarded with a 4.4 MeV deuteron. What is the Q-value of the reaction ?
(a) 22 MeV (Ans)
(b) 30.8 Mev
(c) 22 J
(d) 30.8 J
Explanations : Q-value of reaction = (2 x 13.2 - 4.4)
= (26.4 - 4.4) = 22 MeV
Magnetic field at the centre.
2. A current is flowing in a circular coil of radius r and the magnetic field at the centre is B0. At what distance from the centre on the axis of the coil is the magnetic field B0/27?
(a) ?3 r
(b) 2?2 r(Ans)
(c) ?2 r
(d) 2 r
Explanations : B0 = µ0 Ni/2r
At axis, Baxis = µ0/2 Nir2/(x2 + r2)3/2
? B0/27 = µ0/2 Nir2/(x2 + r2)3/2
? µ0Ni/2 * r * 27 = µ0/2 Nir2/(x2 + r2)3/2
or 27 = (1 + x2/r2)3/2
(3)2 = (1 + x2/r2)
9 = (1 + x2/r2)
8r2 = x2
x = 2?2r
Alternative
The ratio of magnetic field at the centre of circular coil and on its axis is given by
Bcentre/Baxis = (1 + x2/r2)3/2
? B0/ B0/27 = (1 + x2/r2)3/2
or 27 = (1 + x2/r2)3/2
x = 2?2r
3. In the circuit given below, the ammeter reading is zero. What is the value of the resistance R?
(a) 50 ?
(b) 100 ? (Ans)
(c) 200 ?
(d) 400 ?
Explanations : The terminal potential difference across R due to 12 V battery should be equal to 2 V which is the emf of the cell in the loop containing the ammeter.
12 - 12/500 + R * 500 = 2
10 = 12 * 500/500 + R
500 + R = 60 or R = 100 ?
4. In the above circuit, in which of the following cases, the reading of ammeter will change if the ammeter resistance G is changed ?
(a) G = 50 ?
(b) G = 100 ?
(c) G = 500 ?
(d) None of these (Ans)
Explanations : Reading will remain zero, whatever may be the value of ammeter resistance.
