Saturday, October 22, 2011

CBSE Class 7 - Science - Light - Questions & Answers

Class 7 - Ch 15 - Science - Light - Questions & Answers

Question1: 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.

Answers:
1 a) virtual image
b) convex mirror
c) plane
d) real
e) concave lens
 

Question2: 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)

Answers: a-false b-true c-true d-false e-false



Question 3: Match the following:
Column 1 Column 2
(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.
Answers: a-(v)     b-(ii) and (vi)      c-(i)      d-(iii)     e-(iv)

Question 4: State the characteristics of the image formed by a plane mirror.
Answer: 
   1. Image is Virtual
   2. It is behind the mirror
   3. Image is erect (means not inverted)
   4. Image is of same size as the object
   5. Image is at same distance from the mirror as the object is from the mirror. 

Following you tube video nicely explains this.


 
Question 4: 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: The alphabets A, H, I, M, O, T, U, V, W, X, Y will have images in plane mirror exactly the letter itself.The reason for this is such letters are vertically symmetric i.e. vertical plane divides into identical halves.Even if image interchanges, it appear same as the letter.



Q5: What is real image?

Answer: An image which can be obtained on a screen is called a real image.


Q6: When you see yourself in the mirror, what type of image is formed?

Answer: Virtual image. An image which cannot be obtained on a screen is called a virtual image.


Q7: During sunny day, a pool of water appears to lie on the road some distance ahead. What type of image (virtual or real) do we see?


Answer: Virtual image. The pool of water is a mirage (illusion).


Q8: Which type of a surface can act as mirror?

Answer: Polished or a shining surface.


Q9: We can see objects when the lighted reflected from the objects falls upon our eyes. Why can't walls act as mirror even the light is reflected through walls and reach our eyes?

Answer: In case of mirror, the reflected rays of light are parallel and reach our eyes. That's why we can see objects through mirror or any shining surface. Walls surface are rought and reflection of light is diffused. Due to which walls do not act as mirror.


Q10: Name the three important characteristics of the image formed by a plane mirror.

Answer:  Image formed by a plane mirror is:
  1. is erect. 
  2. It is virtual and is of the same size as the object. 
  3. The image is at the same distance behind the mirror as the object is in front of it.

Q11: What is lateral inversion of flat mirror?

Answer: A lateral inversion is reversal of image formed by a mirror, the left side of the object is seen on the right side in the image, and right side of the object appears to be on the left side in the image.


Q12: Real images form on the side of a mirror where the object is, and virtual images form on the opposite side. Is the statement true or false?

Answer: True


Q13: My image is erect and is of the same size. What type of mirror I am looking at?

(a) Concave mirror
(b) Convex Mirror
(c) Plane Mirror
(d) All of these

Answer: (c) Plane Mirror


Q14: Define light. Name three important properties of light.

Answer: Light is a form of energy, which produces the sensation of vision. It has following characteristics:

1. It travels in straight lines and does not bend.
2. It does not require any medium to travel i.e. it travels even in vacuum.
3. Its speed in vacuum is maximum whose value is 3 x 108 m/s.
4. It exhibits phenomena of reflection, refraction and scattering.
5. A white light consists of seven colours (VIBGYOR)


Q15: What type of spherical mirror is used as reflectors in flashlights, and headlights of cars and scooters?

Answer: Concave mirror


Q16: Which type of spherical mirror is used as reflectors at sharp turns or blind corners in big shopping malls or as rear-view mirrors in cars?

Answer: Convex mirror


Q17: Why does a concave mirror called a converging mirror? 

Answer: Concave mirror is called a converging mirror because parallel rays of light fall on the mirror bends towards (converge at) a point called focus.


Q18: Why does a convex mirror called a diverging mirror?

Answer: Convex mirror is called a diverging mirror because parallel rays of light fall on it bend away (diverge) after reflection.


Q19: Identify a spherical lens which is thicker at the Center and thinner at edges.

Answer: Convex lens


Q20: Identify a spherical lens which is thinner at the Center and thicker at edges.

Answer: Concave lens



5 comments:

  1. It helped for Fa . Nothing more than that

    ReplyDelete
  2. not interesting likeother lessons.i.e. nothing useful

    ReplyDelete
    Replies
    1. My bad. Almost forgot to add questions. Thanks for reminding Adding new questions

      Delete