1. What is Huygens’s principle?
a) Every point on a given wave front may be considered as the source of secondary
wavelet which spread out with the speed of light in that medium
b) The new wave front is the forward envelop of the secondary wavelets at the
instant.
2. What are the mean value of RMS value of AC?
(1)
ANS. Mean current is the steady current which sends the same change through a circuit
in the same time as the a.c. does in the half of its time period.
R.M.S. value of the current is that steady current which produces the amount of heat
through resistance in the same time as the alternating current does in the same resistance
in the same time.
3. Write average value of a.c. for one cycle?
(1)
Ans: Average value is zero.
4.
The wavelength of electromagnetic radiation is doubled. What will happen to the
energy of photon?
Ans : It becomes half. ( E = hc/λ )
5.
What is the stopping potential applied to a photocell if the maximum kinetic energy of a
photoelectron is 5𝑒𝑉?
Ans: K.E.=eV0
5eV= eV0
V0 =5 volt(negative)
6. What is the significance of refractive index? (1)
ANS. The refractive index of a medium shows the direction of bending of light i.e. whether the
light will bend towards or away from the normal.
7.
In an a.c. circuit, why is there no power consumption for an ideal inductor? (2)
ANS. The power in an a.c. circuit is wattles phase difference of 90 degree exist between current
and voltage.
Power =Iv . Ev cos .
Since current and voltage have a difference of 900
There for, power= Iv . Ev cos 90 o = 0.
8.
Define resolving power of a telescope.
It is the reciprocal of the smallest angular separation between two point objects whose
images can be just resolved by it.
9.
What is sharpness of resonance?
(2)
ANS. Sharpness of a resonance is defined as a ratio of resonance frequency to the difference in
the frequencies on the both of the current in the circuit falling to 1/√2 of its value at resonance.
10.
What is displacement current ?
(2)
ANS. Displacement current is that current which come into existence in addition to conduction
current when the electrical field and hence the electrical flux is charging with time.
Displacement current is the source of magnetically field.
11.
Two slits in Young’s double slit experiment have widths in the ratio 81:1. What is the
ratio of the amplitudes of light waves from them?
𝐴1
𝑊1
9
= √𝑊2 = 1
𝐴2