Light Test

Result

Light Test - 2

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Weekly Quiz Competition

Question 1
1 / -0

A diver in a swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his water-proof flashlight. Which of the following would be the best way to give that signal?

A
Directing the beam vertically upwards

B
Directing the beam horizontally

C
Directing the beam at an angle to the vertical which is slightly less than the critical angle of incidence for total internal reflection

D
Directing the beam at an angle to the vertical which is slightly more than the critical angle of incidence for total internal reflection

Solution

If the diver directs the light at an angle less than the critical angle, only then the light will refract through the water surface and reach the person sitting on the edge of the lake. If the angle of incidence is greater than the critical angle, the light will remain in the denser medium (i.e. water).
Question 2
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An object, placed at infinity, starts moving towards a convex lens. As it approaches the centre of curvature, the speed of the image is _____ as compared to that of the object, and the size of the image is _____ as compared to that of the object. As the object moves from centre of curvature towards the focus, the speed of the image is _____ as compared to that of the object, and the size of the image is _____ as compared to that of the object.

A
less, smaller, more, larger

B
less, larger, more, larger

C
more, smaller, less, larger

D
more, larger, less, smaller

Solution

When the object is at infinity, its image is formed at focus, and when the object is placed at the centre of curvature, its image is formed at the centre of curvature (2F). So, the object travels a very large distance, whereas the image only travels a distance equal to the focal length (F to 2F). So, the speed of the object is more than the speed of its image.
The size of the image remains less than the size of the object as the object moves from infinity to 2F. When the object is at 2F, the size of the image is the same as the size of the object.
If the object is at the focus of the lens, its image is formed at infinity. So, the object travels a distance equal to the focal length (2F to F), whereas its image travels an infinite distance.
The size of the image becomes more than the size of the object as the object travels from 2F towards F.
Question 3
1 / -0

A ray of light incidents on a plane mirror at an angle of 30°. The deviation produced in the ray (in degrees) is

A
30

B
60

C
90

D
120

Solution

Angle of deviation = 180°- 2(Angle of incidence)
Angle of deviation = 180°- 60°= 120°
Question 4
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Which of the following statements is/are true for irregular reflection?

A
This is the phenomenon due to which a parallel beam of light travelling through some medium, on striking some smooth polished surface, gets reflected as a parallel beam in some other direction.

B
This is the phenomenon due to which a parallel beam of light travelling through some medium, on striking some rough surface, gets reflected in various possible directions.

C
This is the phenomenon due to which a parallel beam of light travelling through some medium, on striking some smooth polished surface, gets reflected in various possible directions.

D
All of the above

Solution

Irregular reflection is the phenomenon due to which a parallel beam of light travelling through some medium, on striking some rough surface, gets reflected in various possible directions.
Question 5
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Which of the following is NOT true about an image formed by a plane mirror?

A
The image is of the same size as the object.

B
The image is formed on the other side of the mirror.

C
The image is of the same colour as the object.

D
The image depicts only the shape of the object.

Solution

The image is formed on the other side of the mirror and having the same size as that of the object. The image produced is just like the object depicting its shape, structure, size, colour, etc.