Lesson 1 of 1 | General Science / Light and Reflection
Light: Reflection and Mirrors
1 practice test
Light: Reflection and Mirrors
Light is a form of energy that helps us see objects. RRB Group D regularly asks 2–4 questions from this chapter.
Key facts
- Light travels in a straight line (rectilinear propagation).
- Speed of light in vacuum ≈ 3 × 10⁸ m/s; it is slower in water and glass.
- Light from the Sun takes about 8 minutes 20 seconds to reach Earth.
Laws of reflection
- The angle of incidence = angle of reflection (∠i = ∠r).
- The incident ray, reflected ray and the normal all lie in the same plane.
Types of mirrors and uses
| Mirror | Image | Common use |
|---|---|---|
| Plane | Virtual, erect, same size, laterally inverted | Dressing mirror |
| Concave (converging) | Real or virtual; can be enlarged | Torch/headlight reflector, shaving & dentist mirror, solar cooker |
| Convex (diverging) | Always virtual, erect, diminished | Rear-view mirror in vehicles, shop security mirrors |
Formula to remember
- Focal length f = R / 2 (R = radius of curvature).
- Mirror formula: 1/f = 1/v + 1/u.
Exam tips
- "Wider field of view" → convex mirror.
- "Enlarged image when close" → concave mirror.
- Plane mirror image is as far behind the mirror as the object is in front.
Analogy
Think of light hitting a mirror like a cricket ball bouncing off a smooth wall. If you throw it at the wall at an angle, it bounces back at the same angle on the other side — that is the law of reflection. A concave mirror is like a satellite dish that collects signals into one point, while a convex mirror is like a bus driver's side mirror that spreads the view to show more of the road.