Light Test

Result

Light Test - 9

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Weekly Quiz Competition

Question 1
1 / -0

What is the nature of image formed in a periscope?

A
Real with lateral inversion

B
Real without lateral inversion

C
Virtual without lateral inversion

D
Virtual with lateral inversion

Solution

In periscope, the two reflections takes place, the image of the one mirror acts an object of the second mirror so image formed is Virtual without lateral inversion.
Question 2
1 / -0

If the angle between the incident ray and the reflected ray is 100°, then the angle made by the reflected ray with normal is

A
40°

B
50°

C
60°

D
30°

Solution

Angle between the incident beam and the reflected ray is 100° (two times the angle of incidence (or angle of reflection)) so the angle of refraction is 50°.
Question 3
1 / -0

If you are standing in front of a plain mirror and find your image at a distance of 20 cm from yourself, then the distance between you and the mirror is

A
20 cm

B
10 cm

C
5 cm

D
40 cm

Solution

Distance of the object from mirror(u) = distance of the image from the mirror (v), so the distance between the object and its image is 2u (= 2v)
Here 2u = 20 cm .
Hence u = 10 cm.
Question 4
1 / -0

Read the following statements and choose the correct option:

Statement A: A ray of light incident normally will retrace its path.
Statement B: The angle of incidence and the angle of reflection both are zero.

A
Both statements A and B are correct and B is the correct explanation of A.

B
Both statements A and B are correct, but B is an incorrect explanation of A.

C
Statement A is correct, but statement B is incorrect.

D
Both statements A and B are incorrect.

Solution

In case of reflection, the angle of reflection is always equal to the angle of incident so when a ray light is incident normally, angle of incidence is zero hence the angle of reflection is also so we can say that when a ray of light incident normally will retrace its path.
Both statements A and B are correct and B is the correct explanation of A.
Question 5
1 / -0

Two mirrors M₁ and M₂ are inclined at an angle θ to each other. A ray parallel to M₂ is incident on M₁and after reflection from M₁ and M₂, it becomes parallel to mirror M₁. The angle between the two mirrors is

A
30°

B
45°

C
60°

D
75°

Solution

Refer to the following figure.

As the first ray is parallel to the horizontal (the angle of incidence is θ), the final reflected ray is also parallel to the first mirror. So, the angle made by the second reflected ray with the horizontal is also θ.
Hence, all the internal angles of the triangle COB are θ.
Hence, 3θ = 180° or θ = 60°
Question 6
1 / -0

When a concave mirror is used as a shaving mirror, then what is the location of the person's face with respect to the focus of the mirror?

A
At focus

B
Between centre of curvature and focus

C
Between pole and focus

D
None of these

Solution

When a concave mirror is used as a shaving mirror, the image should be enlarged and the erect so the person's face should lie in between the pole and the focus.
Question 7
1 / -0

An object, 2 cm high, is placed at a distance of 30 cm in front of a concave mirror of focal length 10 cm. What are the position and size of the image, respectively?

A
15 cm behind the mirror and 1 cm

B
7.5 cm in front of the mirror and 0.5 cm

C
15 cm in front of the mirror and 1 cm

D
7.5 cm behind the mirror and 0.5 cm

Solution

Here the f = - 10 cm, u = - 30 cm
Using the mirror formula

v = -15 cm
Which means image is formed in front of the mirror

Magnification
Hence size of the image is half of the size of the object.
Question 8
1 / -0

An object of length 3 cm is placed in front of a concave mirror at a distance of 30 cm. The focal length of the mirror is 15 cm. What will be the position and length of the image, respectively?

A
30 cm in front of mirror and 3 cm

B
10 cm behind the mirror and 1 cm

C
10 cm in front of the mirror and 1 cm

D
30 cm behind the mirror and 3 cm

Solution

Here the f = - 15 cm, u = - 30 cm
Using the mirror formula

v = -30 cm
Which means image is formed in front of the mirror

Magnification

Hence size of the image is same as the size of the object
Alternate method:
Here the object is placed at the centre of curvature; so its image will be formed at the centre of curvature.
The image is real, inverted and of same size as that of object.
Question 9
1 / -0

The rear-view mirror used in a car is a

A
convex mirror

B
plane mirror

C
concave mirror

D
None of these

Solution

A convex mirror has a large field of view than a plane mirror and the concave mirror so it is used as rear-view mirror in cars.
Question 10
1 / -0

Which of the following options is TRUE in regard to a convex mirror?

A
It produces a virtual and diminished image.

B
It produces a real and magnified image.

C
It produces a real and highly diminished image.

D
None of these

Solution

Image formed by the convex mirror is always erect, smaller and behind the mirror (virtual).
Question 11
1 / -0

The diagram below shows an object OA and its image IB formed by a lens. The image is the same size as the object.

What type of lens is it?

A
Convex

B
Concave

C
Either convex or concave

D
Neither convex nor concave

Solution

If the object is placed beyond the focus the convex lens always produces a inverted and real image beyond the second focus.
Question 12
1 / -0

A real image formed by a convex lens is always ________.

A
on the same side of the lens as the object

B
erect

C
inverted

D
smaller than the object

Solution

Real image formed by the convex lens is always inverted and size of the image depends upon the position of the image .If the object is placed beyond the 2F , the size of the image formed is smaller than the size of the object. If the object is placed between 2F and F size of the image is more than the size of the object.
(1) Object is placed beyond the 2F

(2) Object is placed in between F and 2F

Question 13

1 / -0

In the following question, the position of the object from the convex lens is given in Column I and corresponding image formed is given in Column II. Match the entities in Column I with those in Column II.

Column I	Column II
A. Beyond C	P. Real, inverted and same size
B. At C	Q. Imaginary, erect and enlarged
C. Between C and F	R. Real, inverted and smaller size
D. Between F and O	S. Real, inverted and enlarged size

A - P, B - Q, C - R, D - S

A - R, B -P, C - S, D - Q

A - Q, B - P, C - R, D - S

A - R, B - P, C - S, D - Q

Solution

Correct Answer: A - R, B - P, C - S, D - Q

Question 14
1 / -0

Read the following statements and choose the correct option:

Statement A: A convex lens always forms a real image.
Statement B: A concave lens always forms an imaginary image.

A
Both statements A and B are correct.

B
Statement A is correct, but statement B is incorrect.

C
Statement A is incorrect, but statement B is correct.

D
Both statements A and B are incorrect.

Solution

Statement A is incorrect, but statement B is correct.
Convex lens forms a real and inverted image if the object is placed beyond F When the object is placed between the focus and the optical center of the lens imaginary image is formed.
Concave lens always forms a imaginary and diminished image (smaller than the object size).
Question 15
1 / -0

Read the following statements and choose the correct option:

Statement A: Power of a convex lens is positive.
Statement B: Power is defined as the ability of a lens to converge a parallel beam of light.

A
Both statements A and B are correct.

B
Statement A is correct, but statement B is incorrect.

C
Statement A is incorrect, but statement B is correct.

D
Both statements A and B are incorrect.

Solution

Both statements A and B are correct.
Power of the lens is defined as the ability of the lens to converge a parallel beam of light.
Power of the the lens ,
For the convex lens f is positive , power of lens is positive and for the concave lens f is negative, power of the lens is negative.
Question 16
1 / -0

Power of a combination of two lenses, one convex and the other concave, each of focal length 10 cm is

A
20 D

B
10 D

C
5 D

D
zero

Solution

Focal length of the combination of the lens is given by

Here f₁= 10 cm and f₂ = -10 cm
Question 17
1 / -0

An image of the sun is formed by a concave mirror. The lower half of the mirror is now coated black. Now, which of the following statements is correct?

A
The image size is reduced to half.

B
The size and intensity of the image remain unaltered.

C
The size of the image remains the same, but it is less intense.

D
The size and intensity of the image are reduced to half.

Solution

The number of light rays falling on the mirror is reduced. So, the intensity is reduced, but the size of the image remains the same.
Question 18
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Which of the following statements is/are true for a convex mirror?

A
The image formed by a convex mirror is always virtual.

B
The light rays passing through the centre of curvature of a convex mirror are incident normally on the mirror.

C
The image formed by a convex mirror is always behind the mirror, and is erect.

D
All of the above

Solution

The image formed by a convex mirror is always virtual. The light rays passing through the centre of curvature of a convex mirror are incident normally on the mirror. The image formed by a convex mirror is always behind the mirror, and is erect.
Question 19
1 / -0

In the given figure, PQ is the boundary separating two media and a light ray AO is incident at the boundary.

If n₁= n₂, then the path followed by the refracted ray is represented by

A
1

B
2

C
3

D
4

Solution

Refractive index is the same for both the media, so the ray goes from one medium to another with no refraction, thus path will be straight line.
Question 20
1 / -0

In the above diagram, where is the incident ray coming from?

A
From the object at F

B
From the object at 2F

C
From the object at infinity

D
From the object between F and 2F

Solution

The incident ray is coming from the object placed at infinity.