Light

Q21. When does rainbow appear in the sky?

Ans. Rainbow appears usually after the rain when the sun is low in the sky. The rainbow is seen as a large arc in the sky with many colours.

Q22. We see reflection of trees or buildings in water. Give reason.

Ans. The surface of water can also act like a mirror and change the path of light. Thus, we see reflection of trees or buildings in water.

Q23. Why are concave and convex mirrors called spherical mirrors?

Ans. Concave and convex mirrors are called spherical mirror because their reflecting surfaces are the parts of hollow sphere of glass.

Q24. Give one use each of a concave and a convex mirror.

Ans. Concave mirrors are used by dentists to see an enlarged image of the teeth. Convex mirrors are used as side mirrors in vehicles.

Q25. Why the image formed is erect and is of the same size in stainless steel plate?

Ans. The image formed is erect and is of the same size in stainless steel plate because it acts as a plane mirror.

Q26. What kind of image is formed by convex lens?

Ans. A convex lens can form real and inverted image. When the object is placed very close to the lens, the image formed is virtual, erect and magnified.

Q27. Write the uses of convex mirror.

Ans. Uses of convex mirror

                            i.        They are used as side mirrors in vehicles.

                           ii.        They are used in magnifying glass.

Q28. Do you see colours similar to those in a rainbow somewhere else?

Ans. Yes, when we blow soap bubbles, they appear colourful. Similarly, when light is reflected from the surface of a Compact Disk (CD), we see many colours.

Q29. Tina has prepared a small top with a small circular disc with seven rainbow colours painted on it. When the top rotates it appears nearly white. Why?

Ans. When the top is rotated fast, the colours get mixed together and the top appears to be whitish.

Q30. What is the nature of the image formed by a concave mirror?

Ans. A concave mirror can form a real and inverted image. When the object is placed very close to the mirror, the image formed is virtual, erect and magnified.

Q31. What type of image does the inner side of a spoon show?

Ans. The inner surface of a spoon acts like a concave mirror. Image is erect and larger in size. If we increase the distance of the spoon from our face, we may see our image inverted.

Q32. State the characteristics of the image formed by a plane mirror.

Ans. The image formed by a plane mirror is erect. It is virtual and is of the same size as the object. The image is at the same distance behind the mirror as the object is in front of it.

Q33. What is a virtual image? Give one situation where a virtual image is formed.

Ans.  An image which cannot be obtained on a screen is called a virtual image. The image formed by a plane mirror is virtual image because it could not be obtained on a screen.

Q34. How many colors is white light composed of?

Ans. Sunlight consists of seven colours. The sunlight is said to be white light. This means that the white light consists of seven colours. These are red, orange, yellow, green, blue, indigo and violet.

Q35. Write the uses of concave mirror.

Ans. Concave mirrors are used for many purposes. Doctors use concave mirrors for examining eyes, ears, nose and throat. Concave mirrors are also used by dentists to see an enlarged image of the teeth. The reflectors of torches, headlights of cars and scooters are concave in shape.

Q36. Why does obtaining the image of the sun on a paper with the help of a concave mirror burn the paper?

Ans. Obtaining the image of the sun on a paper with the help of a concave mirror burn the paper because concave mirror converge the sunrays to one point.