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Properties: 1 Mark each
Lighthas the following characteristics:
i) It travels in straight line.
ii) It does not require any medium to travel.
iii) It exhibits phenomena of reflection, refraction and scattering.

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Lens : 1 Mark
Differences : 4 Marks
Lenses are pieces of transparent material bound by curved surfaces. Lenses are of two types:
(i)Concave and (ii)convex lens
Convex lens:
1) It is thick at the centre and thinner at edges.
2) It is called converging lens.
Concave lens:
1) It is thin at the centre and thicker at edges.
2) It is called diverging lens.

:
Concave lens: 1 Mark
Convex lens: 1 Mark
Use: 1 Mark
Convex lens:A converging lens can produce both virtual and real image. It depends on the position of the object placed in front of the lens.
Concave lens: A diverging lens can only produce a virtual image. After refraction from the lens, the rays of light never meet.
Use of convex lens: A refracting telescope uses two convex lenses.
Use of concave lens:Most high-quality cameras, telescopes and binoculars use concave lenses to improve the quality of the images they provide.

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Spherical Mirrors: 1 Mark
Types: 2 Marks
Properties: 2 Marks
The spherical mirror is a curved surface mirror which is a part of the hollow sphere.
Spherical mirrors are of two types:
1) Concave mirror
2) Convex mirror
Properties:

A concave mirror is a spherical mirror whose reflecting surface is curved inwards towards the source of light.Concave mirrorscan produce both real and virtual images. They can be upright (if virtual) or inverted (if real), they can be behind themirror(if virtual) or in front of themirror(if real); they can also be enlarged, reduced, or the same size as the object.
Convex mirror is a spherical mirror whose reflecting is curved outwards. Convex mirrorsproduceonly virtualimages.

:
(a) Explanation with reason: 3 Marks
(b) Solution: 2 Marks
(a) The mirrors commonly used for back and side mirrors are convex in nature. This is done to take advantage of the wider angle that can be reflected by a Convex mirror. A convex mirror, also known as converging mirror, is one which bulges at the middle and is thinner at the edges. While this captures a wider object field, it does so at the cost of image accuracy. The result iscompressionof the reflected image, which makes objects appear smaller and farther away than they really are.
The warning is mentioned in the mirrors so that the driver can accordingly make adjustments and take a well-calculated decision.
(b)The speed of car is 2 m/s which means the car is approaching the truck with a speed of 2 m per second.
The distance between the image of truck and truck will decrease at a double rate. This happens because for each meter the car moves, the mirror becomes closer to the object by 1 meter and also the image becomes 1 meter closer.
This is because the image of the truck will travel a distance twice the distance travelled by the car in equal time.
Hence, the image of the truck will appear to approach the driver with the speed of 2 × 2 = 4 m/s.
As the distance between the truck and car is 20m and the car is going back at a speed of 2m per second, the car will hit the truck in 10 seconds.

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Sub-parts : 1 Mark each
(i) A plane mirror is uniform in width from top, through center, till bottom.
(ii) A Convex mirror is one which feels thicker at middle than at the edges.
(iii) A Concave mirror is thicker at the edges as compared to the center.

:
(a) Explanation: 2 Marks
(b) Explanation: 1 Mark
(a) Shiny objects are those that reflect most of the light that falls on them. Only those substances which have a smooth surface can be shiny. This is because smooth surfaces reflect light uniformly in a particular direction. Because of this, almost all of the light that falls on them get reflected collectively without any considerable loss.
Objects which are not shiny have rough surfaces. When light falls on these rough surfaces, the light get reflected in a random direction, leading to loss in intensity. Hence, such substances are not considered shiny.
(b)Light is made up of seven colours. When the sun shines after the rain and sunlight passes through suspended raindrops this white light from the sun splits into seven constituent colours "VIBGYOR”, which we see as rainbow

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Answer : 1 Mark
Yes, light is necessary to see objects. If there is no light then there will be no reflection from an object and no light will reach our eye and we will not be able to see any object.

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(a) Answer: 1.5 Marks
(b) Answer with explanation: 1.5 Marks
(a) A mirror image formed by a plane mirror is identical in size and shape but is laterally inverted.
If we move our right hand to the right, our image will move the left hand towards the left. It is because in a plane mirror our "left appears right” and "right appears left”. This is called a lateral inversion.
(b) According to the law of reflection, the angle ofincidence is equal to the angle of reflection. If the reflected ray is at an angle of ${90}^{\circ }$ to the incident ray, it implies that the reflected ray will be making an angle of ${45}^{\circ }$ from the normal. Hence, the angle of reflection is${45}^{\circ }$, therefore the angle of incidence of the ray is${45}^{\circ }$ according to the law of reflection.

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Explanation: 2 Marks
If the letters of English alphabet A, H, I, M, O, T, U, V, W, X, Y are kept in front of a plane mirror, then they would form images which exactly look like the original letters of the alphabet. These letters are vertically symmetric. For example, if we divide letters A and U in the middle, then we would find that the right halves are equivalent to the left halves of the letters.

Hence, even if the image interchanges sidewise, it will appear same as the letter.