JEE Physics Ray Optics and Optical Instruments MCQs Set C

Question. A beam of light composed of red and green ray is incident obliquely at a point on the face of rectangular glass slab. When coming out on the opposite parallel face, the red and green ray emerge from
(a) Two points propagating in two parallel directions
(b) Two points propagating in two different non parallel directions
(c) One point propagating in two different directions
(d) One point propagating in the same directions

Answer: A

Question. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index.
(a) Equal to that of glass
(b) Greater than that of glass
(c) Less than that of glass
(d) Less than one

Answer: A

Question. A biconvex lens has a radius of curvature of magnitude 20 cm. Which one of the following options describe best the image formed of an object of height 2 cm placed 30 cm from the lens?
(a) Real, inverted, height = 4 cm
(b) Virtual, upright, height = 1 cm
(c) Real, inverted, height = 1 cm
(d) Virtual, upright, height = 0.5 cm

Answer: A

Question. A converging beam of rays is incident on a diverging lens. Having passed through the lens the rays intersect at a point 15 cm from the lens on the opposite side. If the lens is removed the point where the rays meet will move 5 cm closer to the lens. The focal length of the lens is
(a) –30 cm
(b) 5 cm
(c) –10 cm
(d) 20 cm

Answer: A

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) +50 cm
(c) –150 cm
(d) –15 cm

Answer: A

Question. If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together, what will be their resulting power?
(a) – 0.75 D
(b) + 7.5 D
(c) + 6.5 D
(d) – 6.5 D

Answer: A

Question. A luminous object is placed at a distance of 30 cm from the convex lens of focal length 20 cm. On the other side of the lens, at what distance from the lens a convex mirror of radius of curvature 10 cm be placed in order to have an upright image of the object coincident with it?
(a) 50 cm
(b) 30 cm
(c) 12 cm
(d) 60 cm

Answer: A

Question. A plano-convex lens is made of refractive index 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is
(a) 100 cm
(b) 200 cm
(c) 50 cm
(d) 400 cm

Answer: A

Question. A planoconvex lens (m = 1.5) has radius of curvature 10 cm. It is silvered on its plane surface. Find focal length after silvering
(a) 10 cm
(b) 20 cm
(c) 15 cm
(d) 25 cm

Answer: A

Question. A bubble in glass slab (m = 1.5) when viewed from one side appears at 5 cm and 2 cm from other side, then thickness of slab is
(a) 10.5 cm
(b) 2.5 cm
(c) 3 cm
(d) 3.75 cm

Answer: A

Question. A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will
(a) Become infinite
(b) Remain unchanged
(c) Become small, but non-zero
(d) Become zero

Answer: A

Question. A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is
(a) Zero
(b) 25
(c) 50
(d) Infinite

Answer: A

Question. A convex lens forms a real image 16 mm long on a screen. If the lens is shifted to a new position without disturbing the object or the screen then again a real image of length 81 mm is formed. The length of the object must be
(a) 36 mm
(b) 48.5 mm
(c) 6 mm
(d) 72 mm

Answer: C

Question. An object is placed in front of two convex lenses one by one at a distance u from the lens. The focal lengths of the lenses are 30 cm and 15 cm respectively. If the size of image formed in the two cases is same, then u is
(a) 20 cm
(b) 15 cm
(c) 25 cm
(d) 30 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) 18 cm, 2 cm
(b) 11 cm, 9 cm
(c) 10 cm, 10 cm
(d) 15 cm, 5 cm

Answer: A

Question. An astronomical telescope of tenfold angular magnification has a length of 44 cm. The focal length of the objective is
(a) 40 cm
(b) 4 cm
(c) 440 cm
(d) 44 cm

Answer: A

Question. A microscope is focused on a mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?
(a) 1 cm upward
(b) 2 cm upward
(c) 4.5 cm downward
(d) 1 cm downward

Answer: A

Question. Ray optics is valid, when characteristic dimensions are
(a) Much larger than the wavelength of light
(b) Of the same order as the wavelength of light
(c) Much smaller than the wavelength of light
(d) Of the order of one millimeter

Answer: A

Question. The blue colour of the sky is due to the phenomenon of
(a) Scattering
(b) Dispersion
(c) Reflection
(d) Refraction

Answer: A

Question. Rainbow is formed due to
(a) Refraction and dispersion
(b) Total internal reflection and dispersion
(c) Scattering and refraction
(d) Reflection only

Answer: A

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

Answer: A

Question. The refracting angle of a prism is A, and refractive index of the material of the prism is cot(A/2). The angle of minimum deviation is
(a) 180° – 2A
(b) 90° – A
(c) 180° – 3A
(d) 180° + 2A

Answer: A

Question. Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of 20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of refractive index 1.7. The focal length of the combination is
(a) – 50 cm
(b) – 25 cm
(c) – 20 cm
(d) 50 cm

Answer: D