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INTRODUCTION - Chapter 15 Light class 7 ncert solutions Science - SaraNextGen [2024]


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.

Answer:

(a) An image that cannot be obtained on a screen is called _virtual image_.

A virtual image cannot be obtained on a screen. Only real images can be obtained on a screen.

(b) Image formed by a convex __mirror__ is always virtual and smaller in size.

A convex mirror forms a virtual, diminished and upright image of an object.

(c) An image formed by a __plane__ 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 __real__ image.

Only real images can be obtained on a screen.

(e) An image formed by a concave __lens__cannot be obtained on a screen.

The image formed by concave lens is always virtual. A virtual image cannot be obtained on a screen.

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 forms 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 forms a real image. (T/F)

Answer:

(a)False

The image formed by a convex mirror is always virtual, diminished and erect.

(b) True

The image formed by a concave lens is always virtual, erect and diminished.

(c) True

The image formed by a concave mirror can be real or virtual, enlarged or diminished, and erect or inverted, depending upon the distance of the object from the mirror.

(d) False

The image that can be obtained on a screen is called a real image. Virtual images cannot be obtained on a screen.

(e) False

A concave mirror can form both real and virtual images. The nature of the image depends on the distance of the object from the mirror.

Question 3:

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

 

Column I

 

Column II

(a)

A plane mirror

(i)

Used as a magnifying glass.

(b)

A convex mirror

(ii)

Can form image of objects spread over a large area.

(c)

A convex lens

(iii)

Used by dentists to see enlarged image of teeth.

(d)

A concave mirror

(iv)

The image is always inverted and magnified.

(e)

A concave lens

(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.

(a) (v)Answer:

A plane mirror forms an image which is erect and of the same size as the object.

(b) (ii) and (vi)

A convex mirror forms a virtual, diminished, and upright image and therefore, covers a larger area of view. Its field of view is very large.

(c) (i)

A convex lens can form a magnified image of the object. Therefore, it is used as a magnifying glass.

(d) (iii)

A concave mirror forms an enlarged image of the object. Therefore, it is used to see an enlarged image of teeth by the dentist.

(e) (vi)

The image formed by a concave lens is always virtual, upright and erect.

Question 4:

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

Answer:

The image formed by a plane mirror is erect, laterally inverted, and of the same size as that of the object. The left side of the object appears on the right side of the image. Also, the distance of the image from the plane mirror is same as the distance between the plane mirror and the object.

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.

Answer:

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.

https://img-nm.mnimgs.com/img/study_content/curr/1/7/4/60/391/Chapter%2015_html_m32d09cee.jpg

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

Also Read : Page-No-190:-Chapter-15-Light-class-7-ncert-solutions-Science

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