Class 7 Science NCERT Solutions for Chapter – 15 Light

Light

Question 1.
Fill in the blanks:
(a)
 An image that cannot be obtained on a screen is called .……… .
(b) Image formed by a convex  .……… is always virtual and smaller in size.
(c) An image formed by a  .……… mirror is always of the same size as that of the object.
(d) An image which can be obtained on a screen is called a  .……… image.
(e) An image formed by a concave  .……… cannot be obtained on a screen.

Solution:
(a) virtual image
(b) mirror
(c) plane
(d) real
(e) lens.

Question 2.
Mark ‘T’ if the statement is true and ‘F’ if it is false :
(a)
 We can obtain an enlarged and erect image by a convex mirror. (T/F)
(b) A concave lens always form a virtual image. (T/F)
(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)
(d) A real image cannot be obtained on a screen. (T/F)
(e) A concave mirror always form a real image. (T/F)

Solution:
(a) F
(b) T
(c) T
(d) F
(e) F.

Question 3.
Match the items given in Column I with one more items of Column II.

Column IColumn II
(a) A plane mirror
(b) A convex mirror
(c) A convex lens
(d) A concave mirror
(e) A concave lens
(i) Used as magnifying glass.
(ii) Can form image of objects spread over a large area.
(iii) Used by dentists to see enlarged image of teeth.
(v) The image is erect and of the same size as the object.
(vi) The image is erect and smaller in size than the object.

Solution:
(a)-(v)
(b)-(ii)
(c)-(i)
(d)-(iii)
(e)-(vi).

Question 4.
State the characteristics of the image formed by a plane mirror.

Solution:
In a plane mirror, the image is formed behind the mirror. It is erect, of the same size and is at the same distance from the mirror as the object is in front of it.

Question 5.
Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.

Solution:
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 divided letters A and U in the middle, then we would find that the right halves are equivalent to the left halves of the letters.
NCERT Solutions for Class 7 Science Chapter 15 Light image 1
Hence, even if the image interchanges sidewise, it will appear same as the letter.

Question 6.
What is a virtual image? Give one situation where a virtual image is formed.

Solution:
Image that cannot be formed on a screen is called virtyal image. The image formed by a plane mirror is virtual, because the image cannot be obtained on a screen when placed either in front of the mirror or behind it.

Question 7.
State two differences between a convex and a concave lens.

Solution:

S.No.Convex LensConcave Lens
1.Thick at middle, thin at edge.Thin at middle, thick at edge.
2.Can form real image.Cannot form real image.

Question 8.
Give one use each of a concave and a convex mirror.

Solution:

  1. Concave mirror :Used by dentists to see teeth.
  2. Convex mirror : Used in vehicles as rear view mirror.

Question 9.
Which type of mirror can form a real image?

Solution:
Concave.

Question 10.
Which type of lens forms always a virtual image?

Solution:
Concave.

Choose the correct option in questions 11-13

Question 11.
A virtual image larger than the object can be produced by a
(i)
 concave lens
(ii) concave mirror
(iii) convex mirror
(iv) plane mirror

Solution:
(ii) Concave mirror.

Question 12.
David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be
(i)
 3 m
(ii) 5 m
(iii) 6 m
(iv) 8 m

Solution:
(iii) 6 m

Question 13.
The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be
(i)
 1 m/s
(ii) 2 m/s
(iii) 4 m/s
(iv) 8 m/s

Solution:
(iii) 4 m/s

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