Multiple Choice QuestionsA p-n photodiode is made of a material with a band gap of 2.0 eV. The minimum frequency of the radiation that can be absorbed by the material is nearly
10 x 1014 Hz
5 x 1014 Hz
1 x 1014 Hz
1 x 1014 Hz
B.
5 x 1014 Hz
the p-n photodiode is a semiconductor diode that produces a significant current when illuminated. It is reversed biased but is operated below the breakdown voltage.
Energy of radiation = band gap energy
ie, hv = 2.0 eV
or v= 2.0 x 1.6 x 10-19 / 6.6 x 10-34 = 5 x 1014 Hz
Two radioactive materials X1 and X2 have decay constant 5 λ respectively. If initially, they have the same number of nuclei, then the ratio of the number of nuclei of X1 to that of X2 will be 1/e after a time
λ
λ/2
1/4λ
1/4λ
Two thin lenses of focal lengths f1 and f2 are in contact and coaxial. The power of the combination is
A particle of mass 1 mg has the same wavelength as an electron moving with a velocity of 3 x 106 ms-1. The velocity of the particle is.
(mass of electron = 9.1 x 10-31 kg)
2.7 x 10-18 ms-1
9 x 10-2 ms-1
3 x 10-31 ms-1
3 x 10-31 ms-1
If M (A, Z), MP and Mn denote the masses of the nucleus 
proton and neutron respectively in units of u (1 u = 931.5 MeV/c2) and BE represents its binding energy in MeV, then
M (A,Z) = ZMp + (A-Z)Mn - BE/c2
M (A,Z) = ZMp + (A-Z)Mn + BE
M (A,Z) = ZMp + (A-Z)Mn - BF
M (A,Z) = ZMp + (A-Z)Mn - BF
Two periodic waves of intensities I2 and I2 pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is
I1 + I2
A boy is trying to start a fire by focusing sunlight on a piece of paper using an equal convex lens of focal length 10 cm. The diameter of the sun is 1.39 x 109 m and its mean distance from the earth is 1.5 x 1011 m. What is the diameter of the sun's image on the paper?
9.2 x 10-4 m
6.5 x 10-4 m
6.5 x 10-5 m
6.5 x 10-5 m
Two points are located at a distance of 10 m and 15 m from the source of oscillation. The period of oscillation is 0.05 s and the velocity of the wave is 300 m/s. What is the phase difference between the oscillation of two points?
π/3
2π/3
π
π
Two nuclei have their mass number in the ratio of 1:3. The ratio of their nuclear densities would be
1:3
3:1
(3)1/3 : 1
(3)1/3 : 1
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