A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 1 /2 m away, the number of electrons emitted by photocathode would
decrease by a factor of 4
increase by a factor of 4
decrease by a factor of 2
increase by a factor of 2
B.
increase by a factor of 4
An α-particle of energy 5 MeV is scattered through 180° by a fixed uranium nucleus. The distance of the closest approach is of the order of
1 Å
10^{−10} cm
10^{−12} cm
10^{−15} cm
C.
10^{−12} cm
At closest approach, all the kinetic energy of the α-particle will converted into the potential energy of the system, K.E. = P.E.
The binding energy per nucleon of deuteron (^{2}_{1}H) and helium nucleus (^{4}_{2}He) is 1.1 MeV and 7 MeV respectively. If two deuteron nuclei react to form a single helium nucleus, then the energy released is
13.9 MeV
26.9 MeV
23.6 MeV
19.2 MeV
C.
23.6 MeV
As given,
The binding energy per nucleon of a deuteron (_{1}H^{2} ) = 1.1 MeV
∴ Total binding energy = 2× 1.1 = 2.2 MeV
The binding energy per nucleon of helium (_{2}He^{4} ) = 7 MeV
∴ Total binding energy = 4× 7 = 28 MeV
Hence, energy released in the above process = 28 - 2× 2.2 = 28 - 4.4 = 23.6 MeV
If radius of nucleus is estimated to be 3.6 Fermi then the radius nucleus
6 fermi
8 fermi
4 fermi
5 fermi
A.
6 fermi
The intensity of gamma radiation from a given source is I. On passing through 36 mm of lead, it is reduced to l/8. The thickness of lead which will reduce the intensity to l/2 will be
6 mm
9 mm
18 mm
12 mm
D.
12 mm
When _{3}Li^{7} nuclei are bombarded by protons, and the resultant nuclei are _{4}Be^{8} , the emitted particles will be
neutrons
alpha particles
beta particles
gamma photons
D.
gamma photons
A nuclear transformation is denoted by X(n, α) . Which of the following is the nucleus of element X?
B.
Starting with a sample of pure ^{66}Cu, 7/8 of it decays into Zn in 15 minutes. The corresponding half-life is
10 minutes
15 minutes
5 minutes
7.5 minutes
C.
5 minutes
A nucleus disintegrates into two nuclear parts which have their velocities in the ratio 2:1. The ratio of their nuclear sizes will be
2^{1/3}:1
1:3^{1/2}
3^{1/2}:1
1:2^{1/3}
B.
1:3^{1/2}
Law of conservation of momentum gives
m_{1} v_{1} = m_{2} v_{2}
Two spherical conductor B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged brought in contact with B, then brought in contact with C and finally removed away from both. The new force of repulsion, between B and C is
F/4
3F/4
3F/8
F/8
C.
3F/8