CSIR NET JRF: Physics MCQs (PracticeTest 8 of 35)
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A slab of thickness t and refractive index 1.5 is placed in between point A and B as shown in the above figure. The optical path length between A and B is

(x + t/2 + y)

(x + t + y)

(x + 3/2 t + y)

(x + 5/2 t + y)


Two thin convex lenses, having focal lengths ‘f1’ and ‘f2’ are kept coaxially in air separated by a distance ‘d’ If the space between these two lenses is filled by a liquid of refractive index n, then the equivalent focal length F of the combination will be

(f1f2)/{f1 + f2 (d/n) }

n[f1f2/(f1 + f2 − d) ]

f1f2/(f1 + f2 − d)

f1f2/(f1 + f2 − d/n)


The determinant of the translation matrix describing the transformation of an optical ray through an optical system has a

negative value

nonzero value, which is not unity

zero value

nonzero value, which is unity


The condition for achromatism for two thin lenses of focal lengths f1 and f 2 and made up of the same material (dispersive power w) placed coaxially and separated by a distance ‘d’ is

d = (f1 + f2)/2

d = (f1 − f2)/2

d = f1 + (f2/w)

d = f1 (f2/w)


The fnumber of a camera lens represents

focal length x diameter of. The aperture

focal length/diameter of the aperture

power x diameter of the aperture

power/diameter of the aperture


Two sources of light are said to be coherent if they emit light

of equal amplitudes

having the same wavelength

having a constant phase relationship

having the same intensity


A waveform is divided into Fresnel's halfperiod zones. The total disturbance due to all the zones put together at any external point P is given by

the sum of the disturbance due to all the halfperiod zones

half the sum of the disturbance due to all the halfperiod zones

the disturbance due to the first halfperiod zone

half the disturbance due to the first halfperiod zone


Two stars emitting yellow light of wavelength l are a distance D apart along a line perpendicular to line of vision. They are at a distance R (R > > D) from, the point of observation. If these two stars are to be resolved by a telescope, then the minimum diameter of the lens should be

lD/R

1.22 (lD/R)

1.22 (lR/D)

1.22 lD


A 20 mW laser source having 6 mm aperture sends abeam of wavelength 600 nm to the moon situated at a distance of 4 × 108m. The angular spread of the laser beam on the surface of the moon will be

1.5 × 10 − 15 radian

1.5 × 10 − 11 radian

4.0 × 10 − 7radian

1.0 × 10 − 4 radian


In a plane diffraction grating with N elements, the intensity of the diffracted beam is

proportional to? N

proportional to N

proportional to N2

independent of N.


A given calcite plate behaves as a halfwave plate for a particular wavelength? If the variation of refractive index with k is negligible, then for a light of wavelength 2? the given plate would behave as a

halfwave plate

quarterwave plate

plane polaroid

nonpolarising plate


The wave number of Stokes and antiStokes lines in a Raman spectrum are 18116 cm1 and 18514 cm1 respectively: The wave number of exciting line is

18315

18308

17718

17116


The diameter of nth Newton's ring is observed to be ‘d’ when light of wavelength 490 nm is used. If light of wavelength 640 nm is used, then the corresponding diameter will be

d

0.766 d

1.306 d

1.143 d


In a biprism experiment, a glass plate of refractive index ‘n'and thickness't’ is introduced in the path of light from one of the coherent sources. This. Shifts the central fringe through a distance formerly occupied by mth bright fringe. If? is the wavelength of light from coherent sources, then the thickness of the glass plate introduced is given by

t = (n − 1) (?/m).

t = {1/(n − 1) } (?/m).

t = m?/n − 1

t = m?/(n + 1)
