Light: Mirrors and Lenses

Given: Angle of incidence (angle between incident ray and normal) = 40°

Concept used: By the first law of reflection, the angle of incidence equals the angle of reflection. The angle made by a ray with the mirror = 90° − (angle made with the normal).

Working:
- Angle of reflection = angle of incidence = 40°
- Angle made by the reflected ray with the mirror = 90° − 40° = 50°

Answer: Option (ii) 50°

Concept used: By the laws of reflection:
1. Angle of incidence (i) = Angle of reflection (r), both measured from the normal.
2. The incident ray, normal, and reflected ray all lie in the same plane.

Case (i): Light ray falls along the normal
- The angle of incidence = 0° (ray is along the normal).
- Therefore, angle of reflection = 0°.
- The reflected ray travels back along the same path as the incident ray (i.e., along the normal, but in the opposite direction).
- Angle of reflection = 0°

Case (ii): Mirror is tilted, but the light ray still falls along the normal to the tilted surface
- Even though the mirror is tilted, the ray still falls along the normal, so the angle of incidence = 0°.
- Therefore, angle of reflection = 0°.
- The reflected ray again travels back along the same path as the incident ray.
- Angle of reflection = 0°

Case (iii): Mirror is tilted, and the light ray falls at an angle of 20° from the normal
- Angle of incidence = 20°.
- By the law of reflection, angle of reflection = 20°.
- Draw the normal at the point of incidence on the tilted mirror. Using a protractor, draw the reflected ray on the other side of the normal such that it makes an angle of 20° with the normal.
- Angle of reflection = 20°

*(Note: Use a ruler and protractor to draw the diagrams accurately as instructed. The reflected ray is always on the opposite side of the normal from the incident ray, making an equal angle.)*

Concept used:
- A plane mirror always forms an image that is erect and of the same size as the object.
- A convex mirror always forms an image that is erect and smaller (diminished) than the object.
- A concave mirror (when the object is close) forms an image that is erect and larger (enlarged) than the object.

Matching:

| Image | Mirror |
|---|---|
| (i) — erect image, same size as object | Plane mirror |
| (ii) — erect image, smaller than object | Convex mirror |
| (iii) — erect image, larger than object | Concave mirror |

Answer: Image (i) → Plane mirror; Image (ii) → Convex mirror; Image (iii) → Concave mirror.

Concept used:
- A flat transparent glass piece does not bend light; the object appears the same size and shape.
- A convex lens (converging lens), when the object is placed close, forms an erect and enlarged image.
- A concave lens (diverging lens) always forms an erect and diminished (smaller) image.

Matching:

| Image | Lens/glass type |
|---|---|
| (i) — erect image, same size as object | Flat transparent glass piece |
| (ii) — erect image, larger (enlarged) than object | Convex lens |
| (iii) — erect image, smaller (diminished) than object | Concave lens |

Answer: Image (i) → Flat transparent glass piece; Image (ii) → Convex lens; Image (iii) → Concave lens.

Given: Light is incident along the normal to the mirror.

Concept used: The angle of incidence is measured between the incident ray and the normal at the point of incidence. If the ray travels along the normal, the angle between the ray and the normal is 0°.

Working:
- Angle of incidence = 0° (since the ray is along the normal).
- By the law of reflection, angle of reflection = angle of incidence = 0°.
- The reflected ray travels back along the normal (same path, opposite direction).
- Reflection does take place.

Answer: Option (ii) Angle of incidence is 0°

Concept used:
- A plane mirror reflects the graph sheet image with squares of the same size — the image is neither enlarged nor diminished.
- A concave mirror (when the graph sheet is close) forms an enlarged image — the squares appear bigger.
- A convex mirror always forms a diminished image — the squares appear smaller and more squares are visible.

Identification (based on the images seen in Fig. 10.25):
- The mirror showing the graph squares of the same size → Plane mirror
- The mirror showing the graph squares larger (enlarged) → Concave mirror
- The mirror showing the graph squares smaller (diminished, more squares visible) → Convex mirror

*(Note: Since the actual figure cannot be seen, the identification is based on the standard properties of the three mirrors as described above.)*