Question 1.
A coin placed at the bottom of a tank appears to be raised when water is poured into it. Explain.
Answer
Question 2.
A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal- length 20 cm.
The distance of the object from the lens is 30 cm. Find the:
(i) position
(ii) nature
(iii) size of the image formed.
Answer
Question 3.
(a) Write two rules of the new Cartesian sign conventions for spherical mirrors.
(b) Trace the path of the reflected ray by drawing a figure if it passes from centre of curvature of a
concave mirror.
Answer
Question 4.
Design an activity using concave mirror to prove that it s converging in nature. Also state a method to
find its rough focal length.
Answer
Question 5.
4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of
image and magnification. Describe what happens to the image as the needle is moved farther from
the mirror.
Answer
Question 6.
Rohit placed a pencil perpendicular to principal axis in front of a converging mirror of focal length 30
cm. The image formed is twice the size of the pencil. Calculate the distance of the object from the
mirror.
Answer
Question 7.
Define magnification produced by a spherical mirror in terms of height of a object and image. How is
it related to object and image distance? Explain why magnification is positive for virtual image and
negative for real image?
Answer
Question 8.
An object is placed at a distance of 25 cm away from a converging mirror of focal length 20 cm.
Discus the effect on the nature and position of the image if the position of the object changes from
25 cm to 15 cm. Justify your answer without using mirror formula.
Answer
Question 9.
Write one similarity and one dissimilarity between image formed by plane mirror and convex mirror.
Answer
Question 10.
(a) State Snell’s law of refraction.
(b) When a ray of light travelling in air enters obliquely into a glass slab, it is observed that the light
ray emerges parallel to the incident ray but it is shifted sideways slightly. Draw a ray diagram to
illustrate it.
Answer
Question 11.
A 5cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm.
The distance of the object from the lens is 15 cm. Find the nature, position and size of the image.
Also find its magnification.
Answer
Question 12.
One half of a convex lens is covered with a black paper.
(a)Show the formation of image of an object placed at 2F1, of such covered lens with the help of ray
diagram. Mention the position and nature of image.
(b)Draw the ray diagram for same object at same position in front of the same lens, but now
uncovered. Will there be any difference in the image obtained in the two cases? Give reason for your
answer.
Answer
Question 13.
(a) The refractive index of Ruby is 1.71. What is meant by this statement?
(b) The refractive index of some medium are given below:
Crown glass- 1.52
Water- 1.33
Sapphire- 1.77
In which of the medium is the speed of light
(i)maximum
Advertisements (ii)minimum
Advertisements (iii) Calculate speed of light in sapphire.
Answer
Question 14.
A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 30 cm.
The distance of the object from the lens is 20 cm. Find the:
(a)Position
(b)Nature
(c)Size of the image formed.
Answer
Question 15.
Draw a ray diagram to show refraction of light through a glass slab and label on it the following:
(i)Incident ray
(ii)Refracted ray
(iii)Emergent ray
(iv)Lateral shift (displacement)
Question 16.
If the image formed by mirror for all positions of the object placed in front of it is always virtual and
diminished, state the type of the mirror. Draw a ray diagram in support of your answer. Where are
such mirrors commonly used and why?
Answer
Question 17.
A 6 cm object is placed perpendicular to the principal axis of a convex lens of focal length 15 cm. The
distance of the object from the lens is 10 cm. Find the position, size and nature of the image formed,
using the lens formula.
Answer
Question 17.
The ability of a medium to refract light is expressed in terms of its optical density. Optical density has
a definite connotation. It is not the same as mass density. On comparing two media, the one with the
large refractive index is optically denser medium than the other. The other medium with a lower
refractive index is optically rarer. Also the speed of light through a given medium is inversely
proportional to its optical density.
(i) Determine the speed of light in diamond if the refractive index of diamond with respect to vacuum
is 2.42. Speed of light in vacuum is $3 \times 10^8$m/s.
(ii) Refractive indices of glass, water and carbon disulphide are 1.5, 1.33 and 1.62 respectively. If a ray
of light is incident in these media at the same angle (say $\theta$), then write the increasing order of
the angle of refraction in these media.
(iii) (A) The speed of light in glass is $2 \times 10^8$ m/s and in water is $2.25 \times 10^8$ m/s.
(a) Which one of the two is optically denser and why ?
(b) A ray of light is incident normally at the water-glass interface when it enters a thick glass
container filled with water. What will happen to the path of the ray after entering the glass ? Give
reason.
(iv) (B) The absolute refractive indices of water and glass are 4/3 and 3/2 respectively. If the speed of
light in glass is $2 \times 10^8$ m/s, find the speed of light in (i) vacuum and (ii) water.
Answer
Question 18.
It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.
(i)What should be the range of distance of an object placed in front of the mirror?
(ii)Will the image be smaller or larger than the object? Draw ray diagram to show the formation of
image in this case,.
(iii)Where will the image of this object be, if it is placed 6 cm in front of the mirror? Draw ray diagram
for this situation to justify your answer.
Show the position of pole, principal focus and the centre of curvature in the ray diagram.
Answer
Question 19.
A student has three concave mirrors A, B and C of focal lengths 20 cm, 15 cm and 10 cm respectively.
For each concave mirror he performs the experiment of image formation for three values of object
distance of 30 cm, 10 cm and 20 cm.
Giving reason answer the following:
(a)For the three object distances, identify the mirror which will form an image equal in size to that of
object. Find at least one value of object distance.
(b)Out of the three mirrors, identify the mirror which would be preferred to be used for shaving
purpose.
(c)For the mirror B, draw ray diagram for image formation for any two given values of object
distance.
Answer
Question 20.
An object is placed at infinity from a concave mirror of focal length 10 cm. Find the position and
nature of image formed. Draw a ray diagram to show the formation of image. (Not to scale)
Answer
Question 21.
(a) Define focal length of a spherical lens.
(b) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm
from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens?
Find the size of the image also.
(c) Draw a ray diagram to show the formation of image in the above situation.
Answer
Question 22.
(a) A converging lens forms a real and inverted image of an object at a distance of 100 cm from it.
Where should an object be placed in front of the lens, so that the size of the image is twice the size
of the object? Also, calculate the power of a lens.
(b) State laws of refraction.
Answer
Question 23.
List the new Cartesian sign convention for reflection of light by spherical mirrors. Draw a diagram and
apply these conventions for calculating the focal length and nature of a spherical mirror which forms
a 1/3 times magnified virtual image of an object placed 18 cm in front of it.
Answer
Question 24.
a.One – half of a convex lens of focal length 110 cm is covered with a black paper. Can such a lens
produce an image of a complete object placed at a distance of 30 cm from the lens? Draw a ray
diagram to justify your answer.
b. A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20
cm. The distance of the object from the lens is 15 cm. Find the nature, position and size of the image.
Answer
