Video Lecture
Theory For Making Notes
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Practice Questions (Basic Level)
Q.1
A ray of light falls normally on a refracting face of a prism of refractive index 1.5. If the ray just fails to emerge from the prism. Then the angle of prism is
(a) {{\sin }^{{-1}}}\left( {\frac{2}{3}} \right)
(b) {{\cos }^{{-1}}}\left( {\frac{2}{3}} \right)
(c) {{\sin }^{{-1}}}\left( {\frac{1}{2}} \right)
(d) {{\sin }^{{-1}}}\left( {\frac{1}{2}} \right)
Ans. (a)
Q.2
A glass prism of refractive index 1.5 is immersed in water (m = 4/3). A light beam incident normally on the face AB is totally reflected to reach the face BC, if
(a) \sin \theta \ge \frac{8}{9}
(b) \sin \theta \le \frac{2}{3}
(c) \sin \theta =\frac{4}{5}
(d) \frac{2}{3}<\sin \theta <\frac{8}{9}
Ans. (a)
Q.3
Light is incident normally on face AB of a prism as shown in figure. A liquid of refractive index m is placed on face AC of the prism. The prism is made of glass of refractive index 3/2. The limits of m for which total internal reflection cannot takes place on face AC is
(a) \frac{{3\sqrt{3}}}{4}> m > \frac{{3\sqrt{3}}}{4}
(b) \mu <\frac{{3\sqrt{3}}}{4}
(c) \mu >\sqrt{3}
(d) \mu <\frac{{\sqrt{3}}}{2}
Ans. (b)
Q.4
A ray of light falls on a prism ABC (AB = BC) and travels as shown in figure. The refractive index of the prism material should be greater than
(a) 4/3
(b) \sqrt{2}
(c) 1.5
(d) \sqrt{3}
Ans. (b)
Q.5
We have two equilateral prisms A and B. They are made of materials having refractive index 1.5 and 1.6. For minimum deviation, incident angle will be
(a) small for prism A
(b) small for prism B
(c) equal for both the prisms
(d) can’t be predicted
Ans. (a)
Q.6
A light ray is incident upon a prism in minimum deviation position and suffers a deviation of 34°. If the shaded half of the prism is knocked off, the ray will
(a) Suffer a deviation of 34°
(b) Suffer a deviation of 68°
(c) Suffer a deviation of 17°
(d) Not come out of the prism
Ans. (c)
Q.7
The light ray is incident at angle of 60° on a prism of angle 45°. When the light ray falls on the other surface at 90°, the refractive index of the material of prism m and the angle of deviation d are given by
(a) \mu =\sqrt{{\frac{3}{2}}},\,\,\delta =30{}^\circ
(b) \mu =1.5,\,\,\delta =15{}^\circ
(c) \mu =\frac{{\sqrt{3}}}{2},\,\,\delta =30{}^\circ
(d) \mu =\sqrt{{\frac{3}{2}}},\,\delta =15{}^\circ
Ans. (d)
Q.8
For a material, the refractive indices for red, violet and yellow colour light are respectively 1.52, 1.64 and 1.60. The dispersive power of the material is
(a) 2 (b) 0.45 (c) 0.2 (d) 0.045
Ans. (c)
Q.9
A prism (m = 1.5) has a refracting angle of 30°. The deviation of a monochromatic ray incident normally on its one surface will be (sin48°36¢ = 0.75)
(a) 18°36¢ (b) 22°38¢ (c) 18° (d) 22°1
Ans. (a)
Practice Questions (JEE Main Level)
Q.1
A ray of light makes normal incidence on the diagonal face of a right-angled prism as shown in figure. If \displaystyle \theta = 37o then the angle of deviation is (sin 37o = 3/5)
(a) 53o
(b) 127o
(c) 106o
(d) 90o
Ans (c)
Q.2
\displaystyle \eta number of identical equilateral prisms are kept in contact as shown in figure. If deviation through a single prism is \displaystyle \delta then consider the following statements (m is an integer).
(i) if ( \displaystyle \eta = 2m) deviation through \displaystyle \eta prisms is zero
(ii) if ( \displaystyle \eta = 2m +1) deviation through system of \displaystyle \eta prisms is \displaystyle \delta
(iii) if \displaystyle \eta = 2m deviation through system of \displaystyle \eta prisms is \displaystyle \delta
(iv) if \displaystyle \eta = 2m + 1 deviation through system of \displaystyle \eta prisms is zero
(a) statements (i) & (iii) are true
(b) statements (i) and (ii) are true
(c) statements (i) and (iv) are true
(d) statements (iii) and (iv) are true
Ans (b)
Q.3
Two parallel light rays pass through an isosceles prism of refractive index \sqrt{{3/2}} as shown in figure. The angle between the two emergent rays is
(a) 15o
(b) 30o
(c) 45o
(d) 60o
Ans (b)
Q.4
What is the minimum value of the refractive index for a 90º – 45º – 45º prism which is used to deviate a beam through 90º by total internal reflection?
(a) 3/2
(b) \displaystyle \sqrt{3}
(c) \displaystyle \sqrt{2}
(d) 5/3
Ans (c)
Q.5
Light is incident normally on face AB of a prism as shown in figure. A liquid of refractive index \displaystyle \mu is placed on face AC of the prism. The prism is made of glass of refractive index 3/2. The limits of \displaystyle \pi for which total internal reflection takes place on face AC is
(a) \displaystyle \mu \,>\,\frac{{\sqrt{3}}}{2}
(b) \displaystyle \mu \,<\,\frac{{3\sqrt{3}}}{4}
(c) \displaystyle \mu \,<\sqrt{3}
(d) \displaystyle \mu \,<\frac{{\sqrt{3}}}{2}
Ans (b)
Q.6
A prism having refractive index \sqrt{2} and refracting angle 30o, has one of the refracting surfaces polished. A beam of light incident on the other refracting surface will trace its path if the angle of incidence is
(a) 0o (b) 30o (c) 45o (d) 60o
Ans. (c)
Q.7
A ray of light is incident at an angle i on one surface of a prism of small angle A and emerges normally from the opposite surface. If the refractive index of the material of the prism is m, the angle of incidence i is nearly equal to
(a) \frac{A}{\mu }
(b) \frac{A}{{2\mu }}
(c) mA
(d) \frac{{\mu A}}{2}
Ans. (c)
Q.8
The angle of a prism is A. Its one surface is silvered. Light rays falling at an angle of incidence 2A on first surface retrace the same path after suffering reflection at the second silvered surface. The refractive index of material is
(a) 2 sin A (b) 2 cos A (c) (1/2) cos A (d) tan A
Ans. (b)
Q.9
A thin prism P1 with angle 4° and made from glass of refractive index of 1.54 is combined with another thin prism P2 made from glass of refractive index 1.72 to produce dispersion without deviation. The angle of the prism P2 is
(a) 5.33° (b) 4° (c) 3° (d) 2.6°
Ans. (c)
Q.10
A prism can have a maximum refracting angle of (C = critical angle
(a) 60o (b) C (c) 2C (d) slightly less than 180o]
Ans. (c)
11.
A ray is incident perpendicular to one face of an equilateral prism as in figure. What is the minimum value of the refractive index required for total internal reflection at the second face?
(a) 1.15
(b) 3.0
(c) 1.0
(d) 2.0
Ans (a)
Practice Questions (JEE Advance Level)
1.
In the figure shown, a ray is incident on the face ‘oa’ of the prism at an angle i. The emergent ray is parallel to the face ‘ob’. If the angle of prism is A = 30o and the refractive index µ= \displaystyle \frac{2}{{\sqrt{3}}}, then find the angle of incidence, and the angle of deviation. State whether the deviation is clockwise or anti-clockwise.
Take sin35o = \displaystyle \frac{1}{{\sqrt{3}}}
(a)25o
(b)35o
(c)50o
(d)90o
Ans (a)
2.
A ray is obliquely incident on a prism of refractive index m as shown in figure. Then the maximum value of a for which there is an emergent ray along face AC is given by
(a) \displaystyle \cos \alpha =\mu \sin (\phi -{{\theta }_{c}})
(b) \displaystyle \cos \alpha =\mu \sin (\phi +{{\theta }_{c}})
(c) \displaystyle \cos (\alpha -\phi )=\mu \sin (\phi +{{\theta }_{c}})
(d) \displaystyle \sin \alpha =\mu \cos (\phi -{{\theta }_{c}})
where Θc is the critical angle for total internal reflection.
Ans : (a)
Comprehension Based Question (3 and 4)
A prism of refracting angle 30o is coated with a thin film of transparent material of refractive index 2.2 on face AC of the prism. A light of wavelength 6600 Å is incident on face AB such that angle of incidence is 60o
31.
The angle of emergence, and
[Given refractive index of the material of the prism is ]
(a) angle of emergence is 30
(b) angle of emergence is 50
(c) angle of emergence is 0
(d) angle of emergence is 25
Ans (c)
32.
The minimum value of thickness of the coated film on the face AC for which the light emerging from the face has maximum intensity.
(a) 1200 Å
(b) 1300 Å
(c) 1400 Å
(d) 1500 Å
Ans (d)
Comprehension Based Question (5 and 6)
Two parallel beams of light P and Q (separation d) containing radiations of wavelengths 4000Å and 5000 Å (which are mutually coherent in each wavelength separately) are incident normally on a prism as shown in the figure. The refractive index of the prism as a function of wavelength is given by the relation, m(l) = 1.20 + b/l2 where l in Å and b is positive constant. The value of b is such that the condition for total reflection at the face AC is just satisfied for one wave length and is not satisfied for the other.
5.
Find the value of b
(a) 1.0 x 105 Å2
(b) 3.0 x 105 Å2
(c) 5.0 x 105 Å2
(d) 8.0 x 105 Å2
Ans (d)
6.
Find the deviation of the beams transmitted through the face AC
(a) 27.13o
(b) 30o
(c) 25o
(d) 25.50o
Ans (a)
7.
The cross-section of a prism is shown in the figure. One of its refracting surfaces (AC) is given by y = x2. A ray of light traveling parallel to x-axis is incident normally on face AB and refracted. Find the minimum distance of the incident ray from point A to get refracted ray from surface AC.
(a) h=\frac{{{{\mu }^{2}}-1}}{4}
(b) h=\frac{{{{\mu }^{3}}-1}}{5}
(c) h=\frac{{{{\mu }^{9}}-1}}{3}
(d) h=\frac{{{{\mu }^{5}}-1}}{5}
Ans (a)