CBSE Class 12 Physics Ray Optics And Optical Instruments Worksheet Set 04

Question. An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be
(a) 30 cm away from the mirror
(b) 36 cm away from the mirror
(c) 30 cm towards the mirror
(d) 36 cm towards the mirror

Answer: B

Question. The direction of ray of light incident on a concave mirror is shown by PQ while directions in which the ray would travel after reflection is shown by four rays marked 1, 2, 3 and 4 (Fig. given alongside). Which of the four rays correctly shows the direction of reflected ray?
(a) 1
(b) 2
(c) 3
(d) 4

Answer: B

Question. A concave mirror of focal length 15 cm forms are image having twice the linear dimensions of the object. The position of the object, when the image is virtual, will be
(a) 22.5 cm
(b) 7.5 cm
(c) 30 cm
(d) 45 cm

Answer: B

Question. A short pulse of white light is incident from air to a glass slab at normal incidence. After travelling through the slab, the first colour to emerge is
(a) blue
(b) green
(c) violet
(d) red

Answer: D

Question. Why is refractive index in a transparent medium greater than one?
(a) Because the speed of light in vacuum is always less than speed in a transparent medium
(b) Because the speed of light in vacuum is always greater than the speed in a transparent medium
(c) Frequency of wave changes when it crosses medium
(d) None of the options

Answer: B

Question. Transmission of light in optical fibre is due to
(a) scattering
(b) diffraction
(c) refraction
(d) multiple total internal reflection

Answer: D

Question. You are given four sources of light each one providing a light of a single colour – red, blue, green and yellow. Suppose the angle of refraction for a beam of yellow light corresponding to a particular angle of incidence at the interface of two media is 90°. Which of the following statements is correct if the source of yellow light is replaced with that of other lights without changing the angle of incidence?
(a) The beam of red light would undergo total internal reflection.
(b) The beam of red light would bend towards normal while it gets refracted through the second medium.
(c) The beam of blue light would undergo total internal reflection.
(d) The beam of green light would bend away from the normal as it gets refracted through the second medium.

Answer: C

Question. Which of the following is not due to total internal reflection ?
(a) Working of optical fibre
(b) Difference between apparent and real depth of a pond
(c) Mirage on hot summer days
(d) Brilliance of diamond

Answer: B

Question. An object approaches a convergent lens from the left of the lens with a uniform speed 5 m/s and stops at the focus. The image
(a) moves away from the lens with an uniform speed 5 m/s.
(b) moves away from the lens with an uniform accleration.
(c) moves away from the lens with a non-uniform acceleration.
(d) moves towards the lens with a non-uniform acceleration.

Answer: C

Question. The radius of curvature of the curved surface of a plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will
(a) act as a convex lens only for the objects that lie on its curved side.
(b) act as a concave lens for the objects that lie on its curved side.
(c) act as a convex lens irrespective of the side on which the object lies.
(d) act as a concave lens irrespective of side on which the object lies.

Answer: C

Question. Focal length of a convex lens of refractive index 1.5 is 2 cm. Focal length of lens, when immersed in a liquid of refractive index of 1.25 will be
(a) 10 cm
(b) 7.5 cm
(c) 5 cm
(d) 2.5 cm

Answer: C

Question. A ray of light incident at an angle q on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5° and the prism is made of a material of refractive index 1.5, the angle of incidence is
(a) 7.5°
(b) 5°
(c) 15°
(d) 2.5°

Answer: A

Question. The refractive index of the material of a prism is 2 and the angle of the prism is 30°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace it path (after reflection from the silvered surface) if its angle of incidence of the prism is
(a) 60°
(b) 45°
(c) 30°
(d) zero

Answer: B

Question. A thin prism having refracting angle 10° is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. This refracting angle of second prism should be
(a) 6°
(b) 8°
(c) 10°
(d) 4°

Answer: A

Question. The sky would appear red instead of blue if
(a) atmospheric particles scatter blue light more than red light
(b) atmospheric particles scatter all colours equally
(c) atmospheric particles scatter red light more than blue light
(d) the sun was much hotter

Answer: C

Question. The reddish appearance of rising and setting sun is due to
(a) reflection of light
(b) diffraction of light
(c) scattering of light
(d) interference of light

Answer: C

Question. A setting sun appears to be at an altitude higher than it really is. This is because of
(a) absorption of light
(b) reflection of light
(c) refraction of light
(d) dispersion of light

Answer: C

Question. For relaxed eye, the magnifying power of a microscope is
(a) v₀/u₀ × D/f_e
(b) v₀/u₀ × f_e/D
(c) u₀/v₀ × D/f_e 
(d) u₀/v₀ × (- D/f_e)

Answer: A

Question. If the focal length of objective lens is increased then magnifying power of
(a) microscope will increase but that of telescope decrease
(b) microscope and telescope both will increase
(c) microscope and telescope both will decrease
(d) microscope will decrease but that of telescope will increase

Answer: D

Question. Four lenses of focal length ±15 cm, and ±150 cm are available for making a telescope. To produce the largest magnification, the focal length of the eyepiece should be
(a) +15 cm
(b) +150 cm
(c) –150 cm
(d) –15 cm

Answer: A

Question. The magnifying power of a telescope is 9 When it is adjusted for parallel rays the distance between the objective and eyepiece is 20 cm. The focal length of lenses are
(a) 11 cm, 9 cm
(b) 10 cm, 10 cm
(c) 15 cm, 5 cm
(d) 18 cm, 2 cm

Answer: D

Fill in the Blanks

Question. When the refractive index of the material of the lens is greater than that of the surroundings, then biconvex lens acts as a _________________.
Answer: converging lens

Question. The power of a lens is defined as the _________________ of the angle by which it converges or diverges a beam of light falling at unit distant from the optical centre.
Answer: tangent

Question. A lens of power of –4.0 D means a concave lens of focal length _________________ cm.
Answer: –25 cm

Question. When we apply the sign convention, we see that, for erect and virtual image formed by a convex or concave lens, m is _________________.
Answer: positive

Question. The angle between the emergent ray and the direction of the incident ray is called the _________________.
Answer: angle of deviation

Question. At the minimum deviation, the refraction ray inside the prism becomes parallel to the _________________.
Answer: base

Question. In the visible spectrum, red light is at the long wavelength end (~700 nm) while the _________________ is at the short wavelength end (~400 nm).
Answer: violet light

Question. The largest telescope in India is in Kavalur, Tamil Nadu. It is a _________________ diameter reflecting telescope (cassegrain).
Answer: 2.34 m

Question. The amount of scattering is inversely proportional to the _________________ power of the wavelength.
Answer: fourth

Question. For the same angle of incidence, the angles of refraction in three different medium A, B and C are 15°, 25° and 35° respectively. In medium _________________ velocity of light will be minimum.
Answer: A