Light Test

Result

Light Test - 29

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Weekly Quiz Competition

Question 1
1 / -0

The time in a clock is $$8: 40: 10$$. The time in the image of the clock formed by the plane mirror is

A
$$8 : 40 : 10$$

B
$$8 : 50 : 30$$

C
$$3 : 19 : 50$$

D
None of these

Solution

To find the time in the image of the clock, consider the vertical line passing through the numbers 6 and 12 as the axis about which the needles of the clock are to rotate. The hour hand is at 8 which is two places to the left of the axis. When we take the image, we’ll invert the hour hand to two places to the right of the axis. This means that the hour hand in the image will be at 4. Moving ahead, the minute hand in the clock shows 40 which means it is again at 8, the image of the minute hand will hence be at 4 which means that it’ll mean 20.
But the hour hand will move a bit further away from 8 in the forty minutes that the minute hand takes, hence it will be between the 8th and the 9th marking on the clock. This means the image’s hour hand should be between 3 and 4, not exactly at 4.
Similarly, the second-hand shows 10 which means it is at 2, two places to the right of the. When the image is taken, the second hand will be at 10 which means it’ll show us that it’s 50 seconds.
In the ten seconds, the minute hand moves a bit ahead as well, so we need to consider that.
Now, putting together our entire analysis, we can say that the time shown in the image of the clock will be 3:19:50
(since the hour hand in the image is a bit before 3 and the minute hand is a bit before 4)
Question 2
1 / -0

Which surface will reflect most of the light falling on them ?

A
Rough surface

B
Shining surface

C
Smooth surface

D
Opaque surface

Solution
Question 3
1 / -0

The image of an object formed on the outer surface of the spoon is _______ and _______.

A
Real and inverted

B
Real and erect

C
Virtual and inverted

D
Virtual and erect

Solution

The outer surface of a spoon behaves as a convex mirror.
The image formed by a convex mirror is always virtual and erect. When an object is placed at infinity, the virtual image is formed at focus and the size of the image is smaller.
Question 4
1 / -0

The phenomenon related to the reflection of light is

A
Image of the sun visible on the surface of water

B
Reddish colour of the sky during evening

C
Sun is visible two minutes before the actual sun rise.

D
Green house effect caused by the radiation of the sun

Solution

Reflection is when light bounces off an object. If the surface is smooth and shiny, like glass, water or polished metal, the light will reflect at the same angle as it hit the surface. This is called specular reflection, and image of sun becomes visible on the surface of water.
Question 5
1 / -0

A thick plane mirror shows a number of images of the filament of an electric bulb. Of these, the brightest image is the:

A
First

B
Second

C
Last

D
Fourth

Solution

A thick plane mirror forms a number of images of the filament of an electric bulb. Images formed by the front surface which is unpolished reflect only a small part of the light (say $$10\% $$), while the second image is formed by the polished surface which reflects most of the intensity ($$90\%). Hence the second image is the brightest. The intensity of the next reflections will keep on decreasing.
Question 6
1 / -0

A hairdresser stands with her nose $$20\ cm$$ in front of a plane mirror. For what distance must she focus her eyes in order to see her nose in the mirror?

A
$$40\ cm$$

B
$$50\ cm$$

C
$$30\ cm$$

D
$$60\ cm$$

Solution

From the figure, the image is situated at $$40\ cm$$ from the eye. So at $$40\ cm$$ she focuses her eyes in order to see her nose in the mirror.
Question 7
1 / -0

A man of height $$1.8$$m stands infront of a large vertical plane mirror. The distance of the image from the man if he stands at a distance of $$1.5$$ m from the mirror is?

A
$$1$$ m

B
$$2$$ m

C
$$3$$ m

D
$$4$$ m

Solution

Based on the concept of plane mirror, the image formed by the plane mirror is at the same distance behind the mirror as object in front of the mirror.
So the distance between the man and image will be
$$1.5+1.5= 3 \ m$$
Hence the option C is the right answer.
Question 8
1 / -0

Image formed by convex mirror is?

A
Virtual

B
Real

C
Enlarged

D
Inverted

Solution

The image formed in a convex mirror is always erect, virtual, and diminished in size. Convex mirrors image is usually formed behind the mirror, it is virtual and erect. The location of the image is always between the focal point and vertex of the mirror.
Question 9
1 / -0

Which one of the following statements is not true? The phase difference between two light waves can change:

A
By reflection of one of the waves

B
By the waves travelling along paths of different lengths

C
By the waves travelling through media that have a different refractive indices but the same thickness

D
By being transmitted through a boundary between two media with different refraction indices

Solution
Question 10
1 / -0

Images in spherical mirrors suffer from several defects. Some of which is/are:

A
Diffraction effect

B
The magnification varies with the distance of the object from mirror

C
A point source will not produce a point image

D
All of the above

Solution