NCERT Solutions Class 7 Science Chapter 11 Light and Shadows

Concept used. A luminous object produces its own light. A non-luminous object only reflects light.

1. The Sun is a star, so it gives out light.
2. The Pole Star is also a star, so it is luminous.
3. Mars, Venus, Moon, and a mirror only reflect received light.

Concept used. Materials differ in how much light they pass. A pinhole camera uses straight-line light to form an inverted image.

1. Pinhole camera: forms an inverted image.
2. Opaque object: blocks light completely.
3. Transparent object: passes light almost completely.
4. Shadow: dark region formed behind an object.

Concept used. Light travels in straight lines. A person sees the flame only through a straight, open pipe path.

1. Trace a straight line from the flame through the horizontal pipe.
2. Continue it through the left opening.
3. This opening points at Rekha. Other branches bend away.

Concept used. A shadow forms opposite the light source. Its direction follows a straight line from source past object.

1. The Sun is above and right of the boy.
2. Rays travel downwards and leftwards.
3. The shadow must stretch to the lower left, as in (d).

Concept used. Torch rays spread. A ball near the torch blocks a wider cone and makes a larger wall shadow.

1. In (i), the ball is near the torch. Its wall shadow is large, which matches option (b).
2. In (ii), it is near the wall. Its shadow is smaller, which matches option (a).
3. Therefore the complete mapping is (i) to (b), and (ii) to (a).

Concept used. Shadow size depends on source distance. Removing the blocker passes light. Separate sources form separate shadows.

1. Torch close to ball: larger shadow.
2. Torch far away: smaller shadow.
3. Ball removed: bright spot.
4. Two torches: two shadows.

Concept used. A pinhole camera forms an inverted image because top and bottom rays cross at the hole.

1. Use the same tree outline shown in Fig. 11.19.
2. Rotate the complete outline through 180°.
3. The canopy appears below and the long trunk with its base appears above.

Concept used. A plane mirror causes lateral inversion. Reflection makes rays appear to come from corresponding points behind the mirror. This reverses the front-back direction. When we face the object and its image, that reversal is perceived as left-right interchange. Top and bottom stay unchanged.

1. Face the name towards the mirror.
2. Copy every letter in its left-right reversed form.
3. Reflected rays appear to come from behind the mirror.

Concept used. A higher Sun gives steeper rays and a shorter shadow.

1. (i) Among the given times, the shadow is usually shortest at about 12 PM.
2. (ii) The Sun is highest then. Its rays fall most steeply, so the shadow covers the least horizontal distance. At 9 AM and 4 PM, slanting rays make longer shadows.

Concept used. A mirror interchanges left and right. Vertical symmetry can hide the visible change.

1. A is true because mirror images are laterally inverted.
2. T has vertical symmetry.
3. O has vertical symmetry. Therefore B is true.

Concept used. The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal. Two parallel plane mirrors at 45° turn light through the tube.

1. Put one mirror at the upper bend, tilted 45°.
2. Put the second at the lower bend, parallel to the first.
3. Light enters, reflects down, then reflects out.

Concept used. The Sun is an extended source. It makes a dark full shadow and a lighter partial shadow.

1. Different parts of the Sun's broad disc send rays towards the bird from slightly different directions.
2. Far below a high bird, those rays enter and fill much of the region blocked from other parts of the Sun. The full shadow can end before reaching the ground, while the partial shadow spreads and becomes too faint to notice.
3. Near the ground, there is too little distance for rays from different parts of the Sun to fill the blocked region. The shadow stays dark and sharp.