SCRA Question-Paper Contributed by Prthyusha updated on Sep 2019

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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.