Q1. Define the principal focus of a concave mirror.
Ans: It is a point on the principal axis where light rays parallel to the principal axis converge after reflection.

Q2. What is the nature of the image formed by a plane mirror?
Ans: The image is virtual, erect, and laterally inverted.

Q3. Write the mirror formula.
Ans: 1/f = 1/v + 1/u

Q4. What is the speed of light in air?
Ans: Approximately 3 × 108 m/s.

Q5. State one use of concave mirror.
Ans: Used in torches and shaving mirrors.

Q6. What is meant by refraction of light?
Ans: Bending of light when it passes from one medium to another.

Q7. What is lateral inversion?
Ans: The left-right reversal of an image in a plane mirror.

Q8. Name the mirror used by a dentist.
Ans: Concave mirror.

Q9. Define angle of incidence.
Ans: The angle between incident ray and normal at the point of incidence.

Q10. Why does a pencil appear bent when placed in water?
Ans: Due to refraction of light at the interface of air and water.

Q11. State the laws of reflection of light.
Ans: (1) Angle of incidence = angle of reflection. (2) Incident ray, reflected ray and normal lie in the same plane.

Q12. Differentiate between real and virtual image.
Ans: Real image: Formed on screen, inverted. Virtual image: Cannot be captured, erect.

Q13. What is meant by the term “refractive index”?
Ans: Ratio of speed of light in vacuum to that in the medium, n = c/v.

Q14. Why do stars appear to twinkle?
Ans: Due to atmospheric refraction and changing density layers in Earth’s atmosphere.

Q15. A concave mirror forms an image twice the size of the object. If the focal length is 10 cm, find the object distance.
Ans: Use mirror formula with magnification m = -2, focal length f = -10 cm. Object distance = -15 cm.

Q16. What is the power of a lens whose focal length is 25 cm?
Ans: Power P = 100/f = 100/25 = +4D (convex lens).

Q17. Draw a ray diagram for the image formed by a convex mirror when the object is at infinity.
Ans: Image forms at focus, is virtual, erect and diminished.

Q18. Write one difference between convex and concave lens.
Ans: Convex converges light; concave diverges it.

Q19. State the relation between focal length and radius of curvature.
Ans: f = R/2.

Q20. What is the magnification for a plane mirror?
Ans: Magnification = +1.

Q21. Derive the mirror formula with proper diagram.
Ans: Using geometry in ray diagram, derive 1/f = 1/v + 1/u. (Refer NCERT derivation)

Q22. Explain the phenomenon of refraction using a diagram.
Ans: Light bends at the boundary of two media due to change in speed. Diagram shows bending toward/away from normal.

Q23. Draw a ray diagram to show image formation by a concave mirror when object is between focus and pole.
Ans: Image is virtual, erect and magnified, behind the mirror.

Q24. State Snell’s law of refraction and define its terms.
Ans: n = sin i / sin r; where i is angle of incidence, r is angle of refraction.

Q25. Explain the reason behind the bending of light when it enters from air to glass.
Ans: Due to decrease in speed, light bends toward normal.

Q26. State and explain the laws of refraction with an example.
Ans: 1. Incident, refracted ray and normal lie in same plane. 2. Snell’s law. E.g., light bending in glass slab.

Q27. A lens forms a virtual image. What type of lens is it? Support your answer with a diagram.
Ans: Concave lens forms virtual, erect, diminished image. Diagram shows diverging rays.

Q28. How does the apparent depth of a coin in water change due to refraction? Explain.
Ans: Due to bending of light, object appears raised; hence, apparent depth is less.

Q29. Write the characteristics of the image formed by a concave mirror when the object is at the center of curvature.
Ans: Real, inverted, same size, formed at center of curvature.

Q30. Differentiate between reflection and refraction (at least 3 points).
Ans: Reflection: light bounces back; same medium; angle i = angle r. Refraction: light bends; different media; speed changes.