JEE Physics Ray Optics and Optical Instruments MCQs Set C

Question:

• a)

  

• b)

  

• c)

  

• d) xy

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: For the angle of minimum deviation of a prism to be equal to its refracting angle, the prism must be made of a material whose refractive index

• a)

  

• b) Is greater than 2
• c) Is less than 1
• d)

  

Answer:

Question:

• a) 10°
• b) 7°
• c) 5°
• d) 12°

Answer: 10°

Question: Light enters at an angle of incidence in a transparent rod of refractive index n. For what value of the refractive index of the material of the rod the light once entered into it will not leave it through its lateral face whatsoever be the value of angle of incidence?

• a)

  

• b) n = 1.3
• c) n = 1
• d) n = 1.1

Answer: 

Question:

• a) 60°
• b) 45°
• c) 30°
• d) 75°

Answer: 60°

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: Two points propagating in two parallel directions

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: Equal to that of glass

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:  Real, inverted, height = 4 cm

Question:

• a) 45°
• b) 60°
• c) Zero
• d) 30°

Answer: 45°

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: –30 cm

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a) 9.2 × 10^–4 m
• b) 12.4 × 10^–4 m
• c) 6.5 × 10^–4 m
• d) 6.5 × 10^–5 m

Answer: 9.2 × 10^–4 m

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: +15 cm

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: – 0.75 D

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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:  50 cm

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:  100 cm

Question:

• a) IV
• b) Same in all
• c) II
• d) I

Answer: IV

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: 10 cm

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:  10.5 cm

Question: A bulb is located on a wall. Its image is to be obtained on a parallel wall with the help of a convex lens. If the distance between the two walls is d, then required focal length will be

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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:  Become infinite

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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:  Zero

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Which of the following is incorrect?

• a)

  

• b)

  

• c) Spherical aberration is minimized by achromatic lens
• d) If the image of distant object is formed in front of the retina then defect of vision may be myopia

Answer:

Question:

• a) 5 m
• b) 2.5 m
• c) 1.25 m
• d) 1 m

Answer: 5 m

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:  36 mm

Question:

• a)

  

• b)

  

• c)

  

• d) None of these

Answer:

Question: The minimum magnifying power of a telescope is M. If focal length of its eye lens is halved, the magnifying power will become

• a) 2M
• b) 3M
• c) 4M
• d)

  

Answer: 2M

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:  20 cm

Question:

• a) Correct myopia
• b) Correct presbiopia
• c) Correct hypermetropia
• d) Correct astigmatism

Answer: Correct myopia

Question:

• a) 4f
• b) 2f
• c) 

  

• d) f

Answer:  4f

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: 18 cm, 2 cm

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: 40 cm

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:  1 cm upward

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: Much larger than the wavelength of light

Question: The blue colour of the sky is due to the phenomenon of

• a) Scattering
• b) Dispersion
• c) Reflection
• d) Refraction

Answer: Scattering

Question: Rainbow is formed due to

• a) Refraction and dispersion
• b) Total internal reflection and dispersion
• c) Scattering and refraction
• d) Reflection only

Answer:  Refraction and dispersion

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: Microscope will decrease but that of telescope will increase

Question:

• a) 2 cos A
• b) 2sin A
• c) tan A
• d)

  

Answer: 2 cos 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: 180° – 2A

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: – 50 cm