07: Reflection Of Light : Icse-ix-physics

Home Learn Fast select Course

Change Unit Change Subject Last Menu

ICSE-IX-Physics

07: Reflection of Light

with Solutions -

Note: Please signup/signin free to get personalized experience.

Note: Please signup/signin free to get personalized experience.

10 minutes can boost your percentage by 10%

Note: Please signup/signin free to get personalized experience.

#

#
Section : A
Multiple Choice Questions -7(A)

Qstn #1
According to the law of reflection:
(a) i/r = constant
(b) sin i /sin r = constant
(c) i + r = constant
(d) i = r
Ans : (d) i = r

Qstn #2
The image formed by a plane mirror has the following characteristic:
(a) Erect and diminished
(b) Erect and enlarged
(c) Inverted and of same size
(d) Erect and of same size.
Ans : (d) Erect and of same size

Qstn #3
The image formed by a plane mirror is :
(a) real
(b) virtual
(c) virtual with lateral inversion
(d) real with lateral inversion
Ans : (c) virtual with lateral inversion

#
Section : A-s1
Numerical -7(A)

Qstn #1
The ray is incident on a plane mirror. Its reflected ray is perpendicular to the incident ray. Find the angle of incidence.
Ans : Angle of incidence (i) + Angle of reflection(r) = 90^o
But, as per the laws of reflection, i = r
Therefore, 2 i = 90^o
Or, i = r = 45^o

Qstn #2
A man standing in front of a plane mirror finds his image at a distance 6 metre from himself. What is the distance of man from the mirror?
Ans : Distance between man and his image = 6m
Distance between man and mirror + distance between mirror and image = 6m
But, Distance between man and mirror (object distance) = distance between mirror and image (image distance)
Therefore, distance of man from mirror = 6/2 = 3m

Qstn #3
An insect is sitting in front of a plane mirror at a distance 1 m from it.
(a) Where is the image of the insect formed?
(b) What is the distance between the insect and its image?
Ans : (a) Image of the insect is formed 1m behind the mirror.
(b) Distance between the insect and his image = 1 + 1 = 2 m

Qstn #4
An object is kept at 60 cm in front of a plane mirror. If the mirror is now moved 25 cm away from the object, how does the image shift from its previous position?
Ans : Initially, distance of the object from the mirror = 60 cm.
Therefore, image is formed at a distance 60 cm from the mirror, behind it.
Thus, initial distance between the object and image = 60 + 60 = 120 cm
If the mirror is moved 25 cm away from the object,
The new distance of the object from the mirror = 60 + 25 = 85 cm
The new image is now at a distance 85 cm from the mirror behind it.
Thus, new distance of the image from the object = 85 + 85 = 170 cm
Taking the position of the object as reference point, the distance between the two positions of the image
= new distance of image from the object - initial distance of the image from the object
= (170 - 120) cm = 50 cm
Thus, the image shifts 50 cm away.

Qstn #5
An optician while testing the eyes of a patient keeps a chart of letters 3 m behind the patient and asks him to see the letters on the image of chart formed in a plane mirror kept at distance 2 m in front of him. How far away is the chart seen by the patient?
Ans : Distance between man and chart = 3m
Distance between man and mirror = 2m
Therefore, distance between chart and mirror = 5 m
Now, final image is formed on the mirror, which is at a distance of 2 m from the man, therefore, the chart as seen by patient is (5m + 2m) = 7m away.

#
Section : B

Qstn #1
Two plane mirrors are placed making an angle in between them. Write an expression for the number of images formed of an object placed in between the mirrors. State the condition, if any.
Ans :
If two mirrors make an angle with each other and object is placed in between the two mirrors, the number of images formed is n or (n - 1) depending upon n = 360°/θ° is odd or even.
(a) If n = 360°/θ° is odd,

The number of images formed is n, when the object is placed asymmetrically between the mirrors.
The number of images formed is n-1, when the object is placed symmetrically between the mirrors.

(b) If n = 360^o/θ^o is even, the number of images is always n-1.

Qstn #2
Two plane mirrors are placed making an angle θ° in between them. For an object placed in between the mirrors, if angle is gradually increased from 0 to 180, how will the number of images change: increase, decrease or remain unchanged?
Ans : The number of images formed is given as, n = 360°/θ°
So, if θ is gradually increased, n decreases.

Qstn #3
How many images are formed for a point object kept in between two plane mirrors M₁and M₂at right angles to each other? Show them by drawing a ray diagram.
Ans : For two mirrors kept perpendicular to each other, three images are formed for an object kept in between them.