OBJECTIVETYPE

1. The relation
betwween focal length and radius of
Carrying 1 mark
6. A concave mirror of focal lengthf produces a real image
curvature of a spherical mirror is : n times the size of the object. The distance of the object
(a) R= 2f (b)f= 2/R from the mirror is :
(c) R=f/2 (d) none of these.
2. When does a convex mirror form a (a) (n-1)f (b) (n + 1)f
magnified image? n+1
(a) When the object is between f and R
(b) When object is beyond 2f n

(c) When the object is at f 7. A convex mirror of focal length f produces an image
(d Never.
3. A virtual image larger than the object can be produced of the size of the object. The distance of the
by :
((a)concave mirror (b) convex mirror object from the mirror is :
(c) plane mirror (d) none of these.
4. An object is kept on the principal axis of a concave
mirror of focal length 10 cm, at a distance of 15 cm
(a) nf (b)
)
from its pole. The image formed by the mirror is : (c) (n + 1)f ()n- 1f.
8. An object is placed on the principal axis of a concave
(a) virtual and magnified
(b) virtual and diminished mirror at a distance of (f is the focal length). The
(G) real and magnified 2
(d) real and diminished. (/SC 2018) image will be at:
5. A mirror forms a real and inverted image of an object (a)- 3) (b) 3f
placed in front of it. The mirror is : 3 3
(a) convex mirror (b)concave mirror (c) f2 (d) -
(c) plane mirror (d) all of these.

ANSWERS
1. (a) 2. (d) 3. (a) 4. (c) 5. (b) 6. (c) 7. (d) 8. (a).

VERY SHORTANSWERTYPE Carrying1mark

1. When does a concave mirror form a virtual image? curvature of a concave mirror produces a real
Answer. It does so when the object is placed between the image beyond the centre of curvature.
pole and the focus of the mirror. (ii) for an object placed between the pole and the focus
2. Use the mirror formula to show that: of a concave mirror, the image is always virtual and
(i) an object placed between focus and centre of enlarged.
 680 NOOTAN ISC Physics-XII
(iii) a convex mirror always produces a virtual image, 3. Where will you keep an object in front of a
independent of the location of the object. mirror to get a real and diminished
image? conca,
(iv) the virtual image produced by a convex mirror is Answer. Beyond centre of curvature.
always diminished in size and is located between
the focus and the pole of the mirror.

SHORT ANSWERTYPE Carrying 2mar

reflected
At the front surface of glass, light is partlythen
1. A boy runs with velocityv towards a plane mirror. With refracted light is ref
partly refracted. The inte
what velocity does his image move towards him? repeatedly at the internal surfaces. At each
Answer. 2 v. The image of an object in a plane mirror reflection at the front surface, part of light is refrac
is always as far behind the mirror as the object is in Out.
front the mirro Therefore, the image of the boy moves touching, whether a e.
6. How can we judge, without
towards the mirror through the distance equal to that mirror is plane, concave or
convex?
moved by the boy towards the mirror. In other words, Answer. Let us hold the mirror close to
our face and l
double
the image of the boy approaches the boy with into it. If the (virtual) image of our face is of the sam.
th
the speed of the boy. size as the face, the mirror is plane; if enlarged,
2. A concave (or convex) mirror is
held under water. Will mirror is concave; if diminished, the mirror
is convey
equallv n
its focal length change? 7. Show that the spherical mirror formula holds
Answer. No. The focal length of a small-aperture a plane mirror.
It does
spherical mirror is half the radius of curvature. Answer. Let us put f = o0 in the mirror formul
medium. (The focal
not depend upon the surrounding 1. 1 1
This gives u =- u. It means that the imag:
length of a lens does not change when immersed in .

water.)
preferred to a plane mirror for formed by a plane mirror is as far behind the mirror a
3. Why is a concave mirror
shaving? the object is in front of it. This is what actually happens
and no
Answer:. When the face is placed between the
pole and 8. Why are mirrors used in searchlights parabolic
image
the focus of the concave mirro, a 'large' and erect concave spherical?
of the face is seen in the mirror. In plane mirror, the Answer. In a searchlight, an intense, broad parallel
image is of same size as the face, wherever
the face may beam of light, whose intensity remains undiminished
be. with distance, is required. If a source of light is placed
plane parallel mirrors. at the focus of a large-aperture concave mirror, the
4. An object is placed between two
How many images are formed? Why do
distant images reflected beam is not completely parallel due to
get fainter and fainter?
spherical aberration, but somewhat divergent. But a
object parabolicmirror, when the source is at its focus, reflects
Answe. The image formed by one mirror acts as Hence,
an infinite
for the other, and so on. Hence, theoretically, images a perfectly parallel beam over its entire surface.
distant
number of imagesare formed. Distant and reflections, parabolic mirrors are used in searchlight.
number of 9. What type of miror would you prefer in your
car tor
are formed by larger and larger
light energy isabsorbed. observing traffic at your back and why?
and at each reflection a part of because :
Hence, the images become fainter and
fainter. Answer. We shall prefer a convex mirror
of the traffic
front a thick' glass (i) it gives a much wider field of view
5. A man holding a lighted candle in the same size,
at our back than a plane mirror of
mirror and viewing it obliquely sees a number of images different
of the candle. What is the origin of these
multiple (i1) itgives erect, small images of all objects at
distances.
images? following mirrors.
Answer. The origin of multiple images is the multiple 10. Write any one use for each of the
(b) concave.
reflection of light at the two internal surfaces of glass. (a) convex
Carrying 3marks
LONG ANSWER TYPE [A]
show image formation of an
1. Prove that for a concave mirror, the radius of curvature 3. Draw a ray-diagram to and the focus of a
is twice the focal length. object placed between the pole
among u,v and
2.. Establish the relation between object distance, image concave mirror. Derive the relation
assumptions and sig
distance and radius of curvature for a concave mirror. for this particular case. State the
convention used.
 Reflection of Light: Spherical Mirrors 681
Establish the relation between object distance, image By mistake, he has taken object and image distance
istance and focal length for a convex mirror. from mirror as x and x,, though correct distances are :
5. What is linear
magnification? Obtain expressions for the
linear magnification of the image formed u= x +f and v =x, +f
miro. by a spherical as,
1 1

6. Draw a ray diagram to show the -(xz + f) -(x +)

a concave mirror when the image formation by 1
obiect is kept between its xË + ft X, +f
focus and the pole. Using this -f (xy + f)x + f)
diagram, derive the
magnification formula for the image formed.
7. Examiner assigned a task to the ’ X2 tf +xf + xyf-fx +fx, +2
has to find the focal length of a student, in which he f=x*2
method. The examiner gives certain concave mirror by U-v or

student and asks some questions. State instructions to the (ii) Response is correct.
responses of the student, in each case, arewhether the
incorrect. Give a reason for your answer. correct or 8

(G) EXAMINER: If the

distance of object from the
focus of the concave mirror A
is x, and distance of its
real image from focus is x), then what is the focal
length of the mirror?
1 1 1
STUDENT: -xz)
(-xz) (-x})-’f=+
+
-f as, Im =
(-x)
(ii) EXAMINER : Where will you place an object as,
infront of aconcave mirror to get real, inverted |m|>1
and magnified image? Hence, real, inverted and magnified image is obtained.
STUDENT:Between focus and centre of curvature (iii) Response is correct.
of the mirror. 8
(iii) EXAMINER: When does concave mirror forms
virtual magnified image?
STUDENT:When object is somewhere between its A'
focus and pole.
Answer : (i) Response of the student is incorrect.

ONGANSWER TYPE [B] PASSAGE BASED Carrying 5 marks

Read the passage(s) and answer the following (ii) Name the type of mirror used as shaving or make
questions : up mirror:
(iv) When does a concave mirror forma virtual image?
A manvisited ashopping store with his friend. The owner (v) What is the relation between focal length and
of the store had fixed number of mirrors at different
radius of curvature of a spherical mirror?
locationsto monitor the activities of the customers and Answer. () Convex mirror.
tales persons. The man pícked up some utility items and (ii) Used as rear view mirror in automobiles.
his friend purchased a make-up mirror for his wife. (ili) Concave mirror.
(i) Name the type of mirrors fixed in the store to
Wateh the activities of the customers. (iv) When object is somewhere between focus and pole.
R
(i) Write an another use of this type of mirror. ()f
MERICALS