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 Physics-IIA

36. List - I 3. In single slit diffraction, width of slit is decreased

a) Fresnel’s diffraction by 60%. Then percentage change in width of
central maximum is _____
b) Fraunhofer’s diffraction
c) In interference phase difference is even multiple 1) 60% 2) 90% 3) 120% 4) 150%
of !" 4. Light of wavelength 5000A0 is incident on a
d) In interference phase difference is odd multiple slit. The first minimum of the diffraction pattern
of !" is observed to lie at a distance of 5 mm from the
central maximum on a screen placed at a distance
List - II
of 3 m from the slit. Then the width of the slit
e) Bright band is
f) Source and screen are at finite distance 1) 3 cm 2) 0.3 cm
g) Dark band 3) 0.03 cm 4) 0.06 cm
h) Source and screen are at infinite distance ↑
5. A small aperture is illuminated with a parallel beam
1) a-f, b-h, c-e, d-g 2) a-e, b-g, c-f, d-h of !"= 628 nm. The emergent beam has an angular
3) a-h, b-f, c-e, d-g 4) a-f, b-h, c-g, d-e divergence of 20. The size of the aperture is
1) 9 !"m 2) 18 !"m
3) 27 !"m 4) 36 !"m
ANSWERS
6. In single slit diffraction a = 0.14 mm, D = 2 m and
1) 4 2) 3 3) 2 4) 2 5) 2 distance of second dark band from central maxima
6) 4 7) 2 8) 2 9) 3 10) 1 is 1.6 cm. The wavelength of light is
1) 6500A0 2) 7500 A0
11) 2 12) 4 13) 3 14) 3 15) 1
3) 5600 A0 4) 8500 A0
16) 3 17) 2 18) 2 19) 1 20) 2
7. The width of a slit is 0.012 mm. Monochromatic
21) 4 22) 3 23) 2 24) 2 25) 4
light is incident on it. The angular position of first
26) 2 27) 3 28) 3 29) 3 30) 3 bright line is 5.20 . The wavelength of the light
31) 4 32) 2 33) 2 34) 1 35) 1 incident is __ (Sin 5.20 = 0.0906)
1) 6040 A0 2) 4026 A0
36) 1
3) 5890 A0 S

4) 7248 A0
EXERCISE-IIA
EXERCISE -IIA 8. The distance between the first and the sixth
minima in the diffraction pattern of a single slit is
Diffraction and resolving power: 0.5mm. The screen is 0.5m away from the slit. If
1. A slit of width ‘a’ is illuminated by white light. wavelength of the light used is 5000 A0, then the
0
The first minimum for red light ( !"= 6500A ) will slit width will be
fall at !"= 300 Then ‘a’ will be 1) 5 mm 2) 2.5 mm
1) 3250 A0 2) 1.3 micron 3) 1.25 mm 4) 1.0 mm
3) 6.5 × 10–4 mm 4) 2.6 × 10–4 m 9. The angular resolution of a 10 cm diameter
2. If I0 is the intensity of principle maximum in the telescope at a wavelength of 5000 A° is of the
order of
single slit diffraction pattern, then what will be its
intensity when the slit width is doubled 1) 106 rad 2) 10–2 rad
1) I0 2) I0/2 3) 2I0 4) 4I0 3) 10–4 rad 4) 10–6 rad

254 DOCTORS SERIES for Sr. Elite Students

 60 %
3) width of slit (a) deed by
C
a = 10
,

a = 10 - 60 = 40
z

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2
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= 150 %
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 pract
- Physics-IIA
23. A parallel beam of fast moving eletrons is incident
29. In a single slit diffraction pattern, a light of
normally on a narrow slit. A flueroscent screen is o

placed at a large distance from the slit. If the speed wavelength 6000 A is used. The distance between
of the electron is increased, which of the following the first and third minima in the diffraction pattern
statennts is correct ? is found to be 3 mm when the screen is placed
1) Diffraction pattern is not observed on the screen 50cm away from slits. The width of the slit is
in the case of electrons. ___ # 10 -4 m
2) The angular width of the central maximum of 1) 1 2) 2 3) 3 4) 4
the diffraction pattern will increase.
3) The angular width of central maximum will ANSWERS
decrease
4) The angular width of central maximum will be 1) 2 2) 4 3) 4 4) 3 5) 4
unaffected. 6) 3 7) 4 8) 2 9) 4 10) 3
24. In an experiment of single slit diffraction pattern,
11) 4 12) 2 13) 3 14) 4 15) 3
first minimum for red light coincides with first
maximum of some other wavelength. If wavelength 16) 2 17) 2 18) 4 19) 3 20) 1
of red light is 6600A0, then wavelength of first 21) 1 22) 4 23) 3 24) 2 25) 4
maximum will be :
1) 5500A0 2) 4400A0 3) 3300A0 4) 6600A0 26) 2 27) 3 28) 1 29) 2

25. Light of wavelength 5 × 10–7m is diffracted by an

aperture of width 2 × 10–3m. For what minimum EXERCISE-IIB
distance travelled by the diffracted beam does the
spreading due to diffraction become greater than Assertion (A) & Reason (R) Type Questions
the width of the aperture? In each of the following questions, a statement
1) 4 m 2) 20 m 3) 18 m 4) 8m of Assertion (A) is given followed by a corresponding
o
statement of Reason (R) just below it. Of the statement
26. A monochromatic light of wavelength 6000 A
mark the correct answer.
is incident on the single slit of width 0.01mm. If
the diffraction pattern is formed at the focus of the 1) Both ‘A’ and ‘R’ are true and ‘R’ is the correct
convex lens of focal length 20cm, the linear width explanation of ‘A’.
of the central maximum is 2) Both ‘A’ and ‘R’ are true and ‘R’ is not the correct

spread
1) 60 mm 2) 24 mm 3) 120 mm 4) 12 mm explanation of ‘A’
3) ‘A’ is true and ‘R’ is false see
27. A microwave of wavelength 2.0cm falls normally
on a slit of width 4.0cm. The angular speed of the
-
4) Both A and R are false back
central maxima of the diffraction pattern obtained >
Diffraction and Resolving power :
on a screen 1.5m away from the slit, will be
Dagel .

1. (A) : Radio waves diffract pronouncedly around

1) 30o 2) 15o 3) 60o 4) 10o the sharp edges of the buildings than visible
28. A parallel beam of monochromatic light of light waves.
o
(R) : Wave length of radio waves is comparable to
wavelength 5000 A is incident normally on a
the dimension of the edges of the building.
single narrow slit of width 0.001 mm. The light is
focussed by convex lens on screen, placed on its 2. (A) : Diffraction is common in sound but not
focal plane. The first minima will be formed for common in light waves.
the angle of diffraction is _____ (degree) (R) : Wavelength of light is more than the
1) 30o 2) 45 3) 60o 4) 90o wavelength of sound.

256 DOCTORS SERIES for Sr. Elite Students