Class 10 Physics MCQs
Chapter 1: Light – Reflection and Refraction
Instructions: Each question carries 1 mark. Click “Show Solution” to verify your answer.
1. The focal length of a concave mirror is 15 cm. Its radius of curvature is:
Answer: c) 30 cm
Explanation: Radius of curvature (R) = 2 × Focal length (f) = 2 × 15 cm = 30 cm.
2. A ray of light travels from air to glass (n=1.5). The angle of refraction will be:
Answer: b) Less than the angle of incidence
Explanation: When light travels to a denser medium (air to glass), it bends towards the normal, reducing the angle of refraction.
3. The magnification produced by a plane mirror is:
Answer: a) +1
Explanation: Plane mirrors always produce images of same size as object with magnification +1.
4. A concave mirror forms a real image of an object placed at 20 cm from the mirror. If the image is formed at 40 cm, the focal length is:
Answer: b) 13.3 cm
Explanation: Using mirror formula: 1/f = 1/v + 1/u = 1/40 + 1/20 = 3/40 ⇒ f = 40/3 ≈ 13.3 cm
5. The refractive index of water is 1.33. The speed of light in water will be:
Answer: c) 2.25 × 10⁸ m/s
Explanation: Speed in water = (Speed in vacuum)/n = (3×10⁸)/1.33 ≈ 2.25×10⁸ m/s
6. A convex lens forms a virtual image when the object is placed:
Answer: d) Between F and the optical center
Explanation: Convex lenses form virtual, erect and magnified images when object is placed between F and optical center.
7. The power of a lens is +2.0 D. Its focal length is:
Answer: a) +50 cm
Explanation: f = 1/P = 1/2 = 0.5 m = 50 cm (Positive for convex lens)
8. In refraction, light bends towards the normal when it travels:
Answer: a) Air to water
Explanation: Light bends towards normal when entering denser medium (air→water).
9. The mirror used as a rear-view mirror in vehicles is:
Answer: b) Convex
Explanation: Convex mirrors provide wider field of view, making them ideal for rear-view mirrors.
10. The SI unit of power of a lens is:
Answer: b) Dioptre
Explanation: The power of a lens is measured in dioptre (D), where 1 D = 1 m⁻¹.
Answer Key
| Q. No. | Answer | Key Concept |
|---|---|---|
| 1 | c | Mirror formula (R = 2f) |
| 2 | b | Refraction at denser medium |
| 3 | a | Plane mirror properties |
| 4 | b | Mirror formula application |
| 5 | c | Refractive index and speed |
| 6 | d | Convex lens image formation |
| 7 | a | Lens power calculation |
| 8 | a | Refraction principles |
| 9 | b | Convex mirror applications |
| 10 | b | Units in optics |