CBSE
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
The diagram shows the energy levels for an electron in a certain atom. Which transition shown represents the emission of a photon with the most energy?
lll
IV
I
II
A.
lll
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
Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm. Approximately, what is the maximum distance at which these dots can be resolved by the eye? [ Take wavelength of light = 500 nm ]
5 m
1 m
6 m
3 m
A.
5 m
A thin glass (refractive index 1.5) lens has an optical power of – 5D in air. Its optical power in a liquid medium with refractive index 1.6 will be
1 D
5/8 D
-1 D
25 D
B.
5/8 D
The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap in (eV) for the semiconductor is
1.1 eV
2.5 eV
0.5 eV
0.7 eV
C.
0.5 eV
Eg = hc/λ
= 0.5eV
therefore correct answer is
0.5 eV
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
A Young’s double slit experiment uses a monochromatic source. The shape of the interference fringes formed on a screen is
hyperbola
circle
straight line
parabola
C.
straight line
A fish looking up through the water sees the outside world contained in a circular horizon. If the refractive index of water is 4/3 and the fish is 12 cm below the surface, the radius of this circle in cm is
B.