CBSE Class 8 Science Spherical Mirrors, Images and Dispersion Worksheet Set 04

Answer: A convex mirror.

Teacher's Note:
1. It gives an erect, diminished image and a wide field of view.
2. This lets the driver see a large area of the road behind.

Answer: Concave mirror and convex mirror.

Teacher's Note:
1. A spherical mirror is a part of a hollow sphere whose one side is polished.
2. The two types differ in which surface reflects the light.

Answer: Reflection.

Teacher's Note:
1. Light that strikes a polished surface bounces back into the same medium.
2. This bouncing back is what lets us see images in mirrors.

Answer: Concave mirror.

Teacher's Note:
1. Its reflecting surface faces the inside of the sphere, like the inner bowl of a spoon.
2. It is also called a converging mirror.

Answer: A real image.

Teacher's Note:
1. A real image is formed when reflected or refracted rays actually meet at a point.
2. Only then can a screen show it.

Answer: A virtual image.

Teacher's Note:
1. The rays only appear to come from a point and do not actually meet there.
2. So no screen can catch such an image.

Answer: The image of your face in a plane mirror (an image formed by a convex mirror is also virtual).

Teacher's Note:
1. The image seems to be behind the mirror.
2. You cannot touch it or catch it on a screen.

Answer: A spectrum (obtained by dispersion of white light).

Teacher's Note:
1. The seven colours are violet, indigo, blue, green, yellow, orange and red (VIBGYOR).
2. Each colour bends by a different amount in the prism, so they separate.

Answer: The focal length of the mirror.

Teacher's Note:
1. It is denoted by f.
2. For a spherical mirror it is half the radius of curvature.

Answer: The outer, bulging surface (it acts as a convex mirror).

Teacher's Note:
1. A convex mirror always gives an erect, diminished, virtual image.
2. The inner surface acts as a concave mirror and usually gives an inverted image.

Answer: (a) ray of light. A ray is the straight line showing the direction of travel of light. A bundle of rays forms a beam.

Teacher's Note:
1. A ray is drawn as a straight line with an arrow.
2. Many rays together make a beam.

Answer: (c) fire. A luminous body produces its own light. The moon only reflects sunlight.

Teacher's Note:
1. Luminous objects are sources of light such as the sun, flame and bulb.
2. Non-luminous objects are seen only because they reflect light.

Answer: (c) virtual and erect. The plane mirror image is behind the mirror, same size, upright and laterally inverted.

Teacher's Note:
1. The image cannot be taken on a screen, so it is virtual.
2. It is upright, so it is erect.

Answer: (b) inverted. Real images formed by mirrors and lenses are inverted with respect to the object.

Teacher's Note:
1. Rays actually meet to form a real image after crossing.
2. This crossing turns the image upside down.

Answer: (b) concave mirrors. A concave mirror held close to the face gives a magnified, erect image.

Teacher's Note:
1. The object lies between the pole and the focus.
2. In that position a concave mirror gives an enlarged virtual image.

Answer: (c) convex mirror. A convex mirror spreads out the reflected rays and shows a large area.

Teacher's Note:
1. The image is smaller but covers more of the surroundings.
2. This is why it is used on vehicles.

Answer: (a) seven colours. White light splits into the seven colours of the spectrum.

Teacher's Note:
1. Newton showed this with a prism.
2. The colours can be recombined to form white light again.

Answer: (b) convex lens. A convex lens bulges outward and converges parallel rays.

Teacher's Note:
1. It is also called a converging lens.
2. A concave lens is thinner in the middle.

Answer: (b) virtual. Parallel rays diverge after reflection from a convex mirror and appear to come from a point behind it.

Teacher's Note:
1. Because the rays only appear to meet, the focus is virtual.
2. A concave mirror has a real focus.

Answer: (b) concave mirror. A concave mirror converges parallel rays to its focus.

Teacher's Note:
1. This property is used in torches, headlights and solar cookers.
2. A convex mirror cannot do this.