In refraction, light waves are bent on passing from on emedium to the second medium, because, in the second medium

the frequency is different
the coefficient of elasticity is different
the speed is different
the amplitude is smaller

Solution

Speed of light is different in different media and different medium has different refractive index.

\(^{1}\mu _{2}=\frac{Speed\, of\, light\, in\, medium\, 1}{Speed\, of\, light\, in\, medium\, 2}\)

In Young’s double slit experiment with sodium vapour lamp of wavelength 589 nm and the slits 0.589 mm apart, the half angular width of the central maximum is

sin^–10.01
sin^–10.0001
sin^–10.001
sin^–10.1

Solution

A monochromatic light wave of wave length λ enters a medium of refractive index μ= 2.Which of the following statements is true ?

speed and frequency are halved and wave length does not change
speed and length are halved and frequency does not change
frequency is frequency are halved while wave length and speed does not change
Wave length, speed and frequency are all halved

Solution

Frequency is the fundamental characteristic of the wave which does not change from one to other medium.

Two sources of light of wavelengths 2500 Å and 3500 Å are used in Young’s double slit expt. simultaneously.Which orders of fringes of two wavelength patterns coincide?

3rd order of 1st source and 5th of the 2nd
7th order of 1st and 5th order of 2nd
5th order of 1st and 3rd order of 2nd
5th order of 1st and 7th order of 2nd

Solution

Let nth fringe of 2500 Å coincide with (n – 2)th fringe of 3500 Å.

∴ 3500 (n – 2) = 2500 × n

1000 n =7000, n =7

∴ 7th order fringe of 1st source will coincide with 5th order fringe of 2nd source.

A parallel beam of fast moving electrons is incident normally on an arrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is in creased, which of the following statements is correct ?

The angular width of the central maximum of the diffraction pattern will increase.
The angular width of the central maximum will decrease.
The angular width of the central maximum will be unaffected.
Diffraction pattern is not observed on the screen in case of electrons.

Solution

In Young’s double slit experiment, the slits are 2 mm apart and a reilluminated by photons of two wavelengths λ₁= 12000 Å and λ₂= 10000 Å. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringe from the other ?

6 mm
4 mm
3 mm
8 mm

Solution

A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperture of diameter ^d⁄₂ in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively

f and ^l⁄₄
^3f⁄₄ and ^l⁄₂
f and ^3f⁄₄
^f⁄₂ and ^l⁄₂

Solution

When the angle of incidence is 60° on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is

√2 × 10⁸ ms^-1
√3 × 10⁸ ms^-1
2 × 10⁸ ms^-1
3 × 10⁸ ms^-1

Solution

A single slit Fraunhoffer diffraction pattern is formed with white light. For what wavelength of light the third secondary maximum in the diffraction pattern coincides with the second secondary maximum in the pattern for red light of wavelength 6500 Å?

4400 Å
4100 Å
4642.8 Å
9100 Å

Solution

In Young’s double slit experiment, the fringes are displaced by a distance x when a glass plate of refractive index 1.5 is introduced in the path of one of the beams. When this plate is replaced by another plate of the same thickness,the shift of fringes is (3/2) x. The refractive index of the second plate is

1.75
1.50
1.25
1.00

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