JEE Physics Ray Optics and Optical Instruments MCQs Set B

Question. In displacement method, convex lens forms a real image of an object for its two different positions. If heights of the images in two cases be 24 cm and 6 cm, then the height of the object is
(a) 12 cm
(b) 6 cm
(c) 36 cm
(d) 3 cm

Answer: A

Question. A plane glass is kept over a coloured word ‘VIBGYOR’, where colour of letters as same as the colours in white light start by letter, the letter which appears least raised is
(a) R
(b) Y
(c) O
(d) V

Answer: A

Question. The near point of a person is 75 cm. In order that he may be able to read book at a distance 30 cm. The power of spectacles lenses should be
(a) +2 D
(b) +3 D
(c) +3.75 D
(d) –2 D

Answer: A

Question. If a lens is moved towards the object from a distance of 40 cm to 30 cm, the magnification of the image remains the same (numarically). The focal length of the lens is
(a) 35 cm
(b) 18 cm
(c) 15 cm
(d) 20 cm

Answer: A

Question. A convex lens of power +2.5 D is in contact with a concave lens of focal length 25 cm. The power of combination is
(a) –1.5 D
(b) 0 D
(c) +1.5 D
(d) +6.5 D

Answer: A

Question. For a telescope in normal adjustment, the length of telescope is found to be 27 cm. If the magnifying power of telescope, at normal adjustment is 8, the focal lengths of objective and eye piece are respectively
(a) 24 cm, 3 cm
(b) 27 cm, 8 cm
(c) 12 cm, 6 cm
(d) 27 cm, 9 cm

Answer: A

Question. A converging lens of focal length 30 cm is placed in contact with another converging lens of unknown focal length, then possible value for focal length of combination is
(a) 15 cm
(b) 60 cm
(c) 36 cm
(d) –12 cm

Answer: A

Question. In displacement method we use a lens of focal length f and distance between object and screen is 60 cm. Possible value for focal length is
(a) 12 cm
(b) 20 cm
(c) 30 cm
(d) –15 cm

Answer: A

Question. Maximum magnification produced by simple micro-scope of focal length f = 5 cm is
(a) 6
(b) 8
(c) 7
(d) 5

Answer: A

Question. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is
(a) 5 cm
(b) 2.5 cm
(c) 15 cm
(d) 10 cm

Answer: A

Question. A tall man of height 6 feet, want to see his full image. Then required minimum length of the mirror will be
(a) 6 feet
(b) Any length
(c) 3 feet
(d) 12 feet

Answer: A

Question. Images formed by an object placed between two plane mirrors whose reflecting surfaces make an angle of 90° with one another lie on a
(a) Circle
(b) Ellipse
(c) Parabola
(d) Straight line

Answer: A

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

Answer: A

Question. In optical fibres, the refractive index of the core is
(a) Greater than that of the cladding
(b) Smaller than that of the cladding
(c) Equal to that of the cladding
(d) Independent of that of the cladding

Answer: A

Question. The refractive index of water is 1.33. What will be the speed of light in water?
(a) 2.25 × 10⁸ m/s
(b) 3 × 10⁸ m/s
(c) 1.33 × 10⁸ m/s
(d) 4 × 10⁸ m/s

Answer: A

Question. Optical fibre are based on
(a) Total internal reflection
(b) Refraction
(c) Less scattering
(d) Less absorption coefficient

Answer: A

Question. The frequency of a light wave in a material is 2 × 10¹⁴ Hz and wavelength is 5000 Å. The refractive index of material will be
(a) 3.00
(b) 1.50
(c) 1.33
(d) 1.40

Answer: A

Question. A ray of light is incident on a 60º prism at the minimum deviation position. The angle of refraction at the first face (i.e., incident face) of the prism is
(a) 30º
(b) Zero
(c) 45º
(d) 60º

Answer: A