A very thin narrow beam of white light is made incident on three glass objects shown below.
Study the nature and behaviour of the emergent beam in all the three cases.
(a) Following are the possibility of two emergent beams being similar. Choose the correct answer:
(i) (i) and (ii)
(ii) (i) and (iii)
(iii) (ii) and (iii)
(iv) No similar emergent beams
Answer
In all 3 cases
- In (i) the emergent beam is white and laterally displaced .
- In (ii) emergent beam is a spectrum of seven colours bent in different angles.
- In (iii) the emergent beam from the second prism is white only .
Similarity between (i) and (iii) as both emergent rays are white in colour
So, the correct answer is (ii) (i) and (iii)
(b) When light enters from air to glass, the angles of incidence and refraction in air and glass are 45° and 30°, respectively. Find the refractive index of glass. (Given that sin 45°= 1/√2 ; sin 30°= 1/2)
(i) √2
(ii) 2 √2
(iii) 1/(√2)
(iv) 1
Ans.
So, the correct answer is (i) √2
(c) The light changes its path as its medium changes. Which of the following is an incorrect statement.
(i) Speed of light is different in different media.
(ii) Light changes its path because light only travels in a straight line.
(iii) Speed of light is dependent on the medium through which it is passing.
(iv) The light chooses the path with minimum time, as it changes its medium.
Ans.
-
Speed of light is different in different media
- Speed of light is less in glass as compared to in air. Hence, we can say that the speed of light is different in different media.
Option (i) is correct
-
Light changes its path because light only travels in a straight line
- Light
doesn't change it’s path
, it just
bends to an angle while
traveling in different media.
Option (ii) is incorrect.
-
Speed of light is dependent on the medium through which it is passing
- This is
true
.
Option (iii) is correct
-
The light chooses the path with minimum time, as it changes its medium
- By definition, light always chooses the path which will take the
least time.
Option (iv) is also correct
So, the correct answer is (ii)
(d) What is the unit of refractive index?
(i) Pascal
(ii) Joule
(iii) No unit
(iv) μ m
Ans.
Refractive index is the ratio of sine of angle of incidence to the sine of angle of refraction which is a constant , hence no unit .
So, the correct answer is (iii) No unit
(e) Light travel fastest in:
(i) Air
(ii) Vacuum
(iii) Glass
(iv) Diamond
Ans.
- Light travel fastest where there no obstructions
- In vacuum, there is no obstructions
- Hence, light travel fastest in vacuum
So, the correct
answer is (ii) vacuum.
