Light Energy — Important Questions

0°

Step 1: When a ray falls normally on a mirror, it means the ray is perpendicular to the mirror surface. Step 2: The angle of incidence is measured between the ray and the normal. Step 3: Since the ray itself travels along the direction of the normal, the angle between them is 0°. Step 4: By the law of reflection, the angle of reflection is also 0°, so the ray retraces its own path. Option A (90°) is the angle the ray makes with the mirror surface, not with the normal.

10 cm

Step 1: One key characteristic of a plane mirror is that the image is as far behind the mirror as the object is in front of it. Step 2: Object distance from mirror = 10 cm. Step 3: Therefore, image distance from mirror = 10 cm. The image is formed 10 cm behind the mirror. Option A (5 cm) is half the object distance — incorrect. Option B (20 cm) is double the distance — also incorrect. Option D (0 cm) would mean the image is at the mirror surface, which is wrong.

Virtual, erect, and same size as the object

A plane mirror forms an image with these characteristics: (1) Virtual — the image cannot be obtained on a screen because the reflected rays diverge and only appear to meet behind the mirror. (2) Erect — the image is upright, not upside down. (3) Same size — the image is neither magnified nor diminished. Option A is wrong because the image is not real or inverted. Options C and D mix up the correct properties. Real images are formed by actual convergence of rays, which does not happen in a plane mirror.

Left hand

This question tests the concept of lateral inversion. A plane mirror swaps the left and right sides of the image. So when you raise your right hand, the image appears to raise its left hand. This is why letters like 'b' look like 'd' in a mirror. This is called lateral inversion — the interchange of left and right sides in the image formed by a plane mirror. The top and bottom are NOT swapped — only the left and right sides are interchanged.