Textbook Solution: Light | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

A. Choose the correct option.

1.
Ans: (c)

2.
Ans: (c)

3.
Ans: (b)

4.
Ans: (b)

B. Fill in the blanks with the correct words.

1.
Ans: An image that cannot be formed on a screen is called a virtual image.

2.
Ans: An image that can be formed on a screen is called a real image.

3.
Ans: A convex mirror always forms diminished, virtual images.

4.
Ans: A convex lens bulges in the middle and is thinner at the edges.

5.
Ans: White light is made of many colours.

C. Write True and False.

D. Answer the following questions.

• The image formed is virtual and can't be formed on a screen.
• The image is upright and of the same size as the object.
• The image is laterally inverted, meaning the left side of the object appears on the right side of the image and vice versa.
• The distance of the image from the mirror is the same as the distance of the object from the mirror.

3.
Ans: Real images are those that can be formed on a screen and can be touched. They are formed when light rays actually meet at a point. They are usually inverted. On the other hand, virtual images cannot be formed on a screen or touched. They are formed when the light rays appear to meet at a point. They are usually upright.

4.
Ans:  Three uses of curved mirrors are:

• Concave mirrors are used in solar power projects to focus the sun's rays in a small region.
• Concave mirrors are also used as dentist's mirrors and shaving mirrors as they form an enlarged image when the object is very close to the mirror.
• Convex mirrors are used as rear-view mirrors in vehicles and in supermarkets and parking lots for a wider field of view

5.
Ans: Concave mirrors are used as dentist's mirrors because when the object (teeth) is very close to the mirror, it forms an enlarged image. This makes it easier for the dentist to examine the teeth.

6.
Ans: You would use a convex lens if you want to focus the Sun's rays to a point. A convex lens converges the parallel rays of light incident on it to a single point, known as the focus.

7.
Ans: We can make a band of colours from white light by using a glass prism or a CD. When white light passes through a prism, it splits into its constituent colours. This band of colours is called a spectrum.

8.
Ans: We can make a coloured disc white by rotating it very fast. This is due to a property of our eyes called persistence of vision. When the disc is rotated very fast, the images of the different colours overlap in our eyes and our brain perceives it as white. This is demonstrated by a Newton's Disc.