Two points separated by a distance of 0.1 mm can just be inspected in a microscope, when light of wavelength 600 Å is used. If the light of wavelength 4800 Å is used, the limit of resolution will become

0.80 mm
0.12 mm
0.10 mm
0.08 mm

Solution

The Fraunhoffer ‘diffraction’ pattern of a single slit is formed in the focal plane of a lens of focal length 1 m. The width of slit is 0.3 mm. If third minimum is formed at a distance of 5mm from central maximum, then wavelength of light will be

5000 Å
2500 Å
7500 Å
8500 Å

Solution

A slit of width a is illuminated by white light. The first minimum for red light (l= 6500 Å) will fall at q= 30º when a will be

3250 Å
6.5 × 10^–4cm
1.3 micron
2.6 × 10^–4cm

Solution

With a monochromatic light, the fringe-width obtained in a Young’s double slit experiment is 0.133 cm. The whole set-up is immersed in water of refractive index 1.33, then the new fringe-width is

0.133 cm
0.1 cm
1.33 × 1.33 cm
^1.33⁄₂cm

Solution

In Young’s double slit experiment, we get 10 fringes in the field of view of monochromatic light of wavelength 4000Å.If we use monochromatic light of wavelength 5000Å, then the number of fringes obtained in the same field of view is

Solution

A radar sends radiowaves of frequency vtowards an aeroplane moving with velocity v_a. A change Δv is observed in the frequency of reflected waves which is higher than original frequency.The velocity of aeroplane is (v_a << c)

\(\frac{c\Delta v}{v}\)
\(\frac{2c\Delta v}{\Delta v}\)
\(\frac{c\Delta v}{2\Delta v}\)
\(\frac{\Delta v}{2c v}\)

Solution

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.

In Fresnel’s biprism expt., a mica sheet of refractive index 1.5 and thickness 6 × 10^–6m is placed in the path of one of interfering beams as a result of which the central fringe gets shifted through 5 fringe widths. The wavelength of light used is

6000 Å
8000 Å
4000 Å
2000 Å

Solution

The wave fronts of a light wave travelling in vacuum are given by x + y + z = c.The angle made by the direction of propagation of light with the X-axis is

0º
45º
90º
cos^–1(1/√3)

Solution

In the phenomena of diffraction of light, when blue light is used in the experiment in spite of red light, then

fringes will become narrower
fringes will become broader
no change in fringe width
None of these

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