# BITSAT: Physics MCQs (Practice_Test 8 of 35)

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1. 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

1. (x + t/2 + y)

2. (x + t + y)

3. (x + 3/2 t + y)

4. (x + 5/2 t + y)

2. Two thin convex lenses, having focal lengths βf1β and βf2β are kept coaxially in air separated by a distance βdβ 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

1. (f1f2)/{f1 + f2- (d/n) }

2. n[f1f2/(f1 + f2 β d) ]

3. f1f2/(f1 + f2 β d)

4. f1f2/(f1 + f2 β d/n)

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

1. negative value

2. non-zero value, which is not unity

3. zero value

4. non-zero value, which is unity

4. 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 βdβ is

1. d = (f1 + f2)/2

2. d = (f1 β f2)/2

3. d = f1 + (f2/w)

4. d = f1- (f2/w)

5. The f-number of a camera lens represents

1. focal length x diameter of. The aperture

2. focal length/diameter of the aperture

3. power x diameter of the aperture

4. power/diameter of the aperture

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

1. of equal amplitudes

2. having the same wavelength

3. having a constant phase relationship

4. having the same intensity

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

1. the sum of the disturbance due to all the half-period zones

2. half the sum of the disturbance due to all the half-period zones

3. the disturbance due to the first half-period zone

4. half the disturbance due to the first half-period zone

8. 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

1. lD/R

2. 1.22 (lD/R)

3. 1.22 (lR/D)

4. 1.22 lD

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

1. 1.5 Γ 10 β 15 radian

2. 1.5 Γ 10 β 11 radian

3. 4.0 Γ 10 β 7radian

4. 1.0 Γ 10 β 4 radian

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

1. proportional to? N

2. proportional to N

3. proportional to N2

4. independent of N.

11. A given calcite plate behaves as a half-wave 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

1. half-wave plate

2. quarter-wave plate

3. plane polaroid

4. non-polarising plate

12. The wave number of Stokes and anti-Stokes lines in a Raman spectrum are 18116 cm-1 and 18514 cm-1 respectively: The wave number of exciting line is

1. 18315

2. 18308

3. 17718

4. 17116

13. The diameter of nth Newton's ring is observed to be βdβ when light of wavelength 490 nm is used. If light of wavelength 640 nm is used, then the corresponding diameter will be

1. d

2. 0.766 d

3. 1.306 d

4. 1.143 d

14. In a biprism experiment, a glass plate of refractive index βn'and thickness'tβ 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

1. t = (n β 1) (?/m).

2. t = {1/(n β 1) } (?/m).

3. t = m?/n β 1

4. t = m?/(n + 1)