NCERT Solutions for Class 10 Science Chapter 9 Light – Reflection and Refraction

Answer: Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on the principal axis after reflection. This point is called the principal focus (F) of the concave mirror.

Answer:
Given: Radius of curvature (R) = 20 cm
Formula: Focal length (f) = R / 2
Calculation: f = 20 / 2 = 10 cm.

Answer: A concave mirror gives an erect and enlarged (virtual) image when the object is placed between its pole (P) and principal focus (F).

Answer: The light ray bends towards the normal. Water is an optically denser medium compared to air. When light passes from an optically rarer medium (air) to an optically denser medium (water), its speed decreases, causing it to bend towards the normal.

Answer:
Given: Refractive index of glass (n) = 1.50, Speed of light in vacuum (c) = 3 × 10⁸ m/s
Formula: n = c / v ⇒ v = c / n
Calculation: v = (3 × 10⁸) / 1.50 = 2 × 10⁸ m/s.

(a) Water
(b) Glass
(c) Plastic
(d) Clay

Correct Answer: (d) Clay (Clay is an opaque material and does not transmit light).

(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus

Correct Answer: (d) Between the pole of the mirror and its principal focus.

(a) At the principal focus of the lens
(b) At twice the focal length (2F₁)
(c) At infinity
(d) Between the optical centre of the lens and its principal focus

Correct Answer: (b) At twice the focal length (2F₁).

Answer:
Given: Power of lens (P) = -2.0 D
Formula: Focal length (f) = 1 / P (in metres)
Calculation: f = 1 / (-2.0) = -0.5 m = -50 cm.
Since the focal length and power are negative, it is a concave lens (diverging lens).