56. In case of a real and inverted image, the magnification of mirror is:
(A) positive and large
(B) negative
(C) positive and small
(D) negative and large
Answer:
(B) negative
Explanation:
According to standard optical sign convention, a real and inverted image has a negative height relative to the object, resulting in a negative magnification value.
57. A convex lens of power +4D is brought in contact with a concave lens of power -2D. The power of the lens combination is:
(A) + 6D
(B) + 2D
(C) -2D
(D) -6D
Answer:
(B) + 2D
Explanation:
The total power of lenses in contact is the algebraic sum of their individual powers. .
58. Twinkling of stars is due to atmospheric:
(A) dispersion of light by water droplets.
(B) scattering of light by dust particles.
(C) refraction of light by different layers of varying refractive indices.
(D) internal reflection of light by clouds.
Answer:
(C) refraction of light by different layers of varying refractive indices.
Explanation:
Starlight continuously bends (refracts) as it passes through Earth’s atmosphere, which consists of multiple layers of air with fluctuating temperatures and refractive indices, causing the twinkling effect.
59. Refractive index of glass is maximum for light of:
(A) red colour
(B) violet colour
(C) yellow colour
(D) blue colour
Answer:
(B) violet colour
Explanation:
The refractive index of a medium is inversely proportional to the wavelength of light. Since violet light has the shortest wavelength in the visible spectrum, glass has the maximum refractive index for it.
60. The bluish colour of water in deep sea is due to:
(A) the presence of algae and other plants found in water.
(B) reflection of sky in water.
(C) scattering of light
(D) absorption of light by sea.
Answer:
(C) scattering of light
Explanation:
Water molecules strongly absorb longer wavelengths (reds and yellows) and scatter the shorter wavelengths (blue light) in all directions, which gives deep bodies of water their bluish appearance.
