Test: How things work - CTET & State TET MCQ

Plane mirrors don't usually form real images. They form "virtual images" of real objects.
However, things can be arranged so that a plane mirror does form a real image. A convergent light beam can do this.

Air is transparent because air contains so few atoms, light waves run into very few of them when they shine through air. The molecules of air are smaller than the wavelength of the light. Due to this reason, particles of air weakly interact with visible light and reflect little or no light to our eyes. 
Transparent material allows all the light to pass through it. In other words transmission is the property of light to permit the passage of light with some or none of the incident light being absorbed or scattered in the process. Since, air is transparent, it transmits almost whole of light.

Light changes its direction after reflection. As we move the object away from the light source, the shadow becomes larger as the distance between object and the light source increases. Reflection is possible from rough surface also. 

Figure (iii) is periscope which is used to see around the corners. It is based upon the principle of rectilinear propagation of light and reflection of light.

The correct answer is 3. Either I or III.

Explanation:

• I. Move away from the mirror: As you move farther away from the mirror, the amount of your body that you can see in the mirror increases. This happens because the angle of view widens as the distance increases, allowing more of your body to be reflected in the mirror.

• II. Move towards the mirror: Moving closer to the mirror will actually decrease the amount of your body you can see because the angle of view narrows. Therefore, this action would not help you see your full image.

• III. Use a mirror whose height will allow you to see your full image: Using a taller mirror that reflects your entire body is an obvious solution to seeing your full image.

So, either moving away from the mirror (I) or using a larger mirror (III) would allow you to see your full image.

Glass is a transparent material. It allows light to pass through it.

The shadows are formed when the opaque object cuts off the light from the source. Since glass is transparent, it allows the light to pass through it. So no dark shadow is formed.

Transparent material allows light to pass through it and opaque object obstructs it.

A colored plastic bottle is an opaque material. When a light beam is incident on it, a shadow will form on the screen can easily pass through the transparent material.

Translucent objects allow only a small part of light to pass through them.

Book is an opaque object and hence does not allow the light of torch to pass through it. As there is no light on the ring, hence no image will be formed and the screen will remain dark due to absence of any light ray.

The image formed in the plane mirror is always of the same size as that of the object.

Polished glass of red colour reflects some of the light incident on it so images of the both persons are formed on it.

Correct Answer :- d

The image given in the question is of a periscope. It uses plane mirrors and multiple reflection to see the image. It is used in submarines.

The image formed by a plane mirror is always virtual, upright and of the same shape and size as the object it is reflecting. The image of object 'O' is seen at the same distance from the mirror as the distance between the object and the mirror. Therefore, the image appears to be at position 'b' after first reflection and on second reflection for the person it appears to be at 'd'.

A glass tumbler is a transparent substance which allows light to pass through it easily.

As u = 

⇒ v = −R

Shadow formed is larger in the morning and evening as compare to the shadow at noon because at noon the sun is at top of the stick.