Reflection Test - 6

When a light wave is reflected from an object, it changes not only its amplitude but also its phase according to the properties of the object at a particular point. The velocity and momentum are just reversed in another direction.

On reflection from a plane surface velocity and amplitude of the incident ray changes whereas wavelength and frequency does not change.

When a wave or a pulse is reflected normally from the surface of a denser medium back into the rarer medium, then tere is a phase difference of π. According to electromagnetic theory When a light beam falls on a boundary of two media, then one part of it will be reflected and other part will be refracted. If refractive index of a medium, where the electromagnetic wave is refracted, is greater than the medium incident, then phase of reflected ray will be reverse with respect to the incident beam. As a result of which the wave suffers a phase change of π.

As we know that frequency of the light ray depends upon the source only.

It only depends on the type of source and it can not change due to medium

so we will have

so when medium changes then frequency remains the same while wavelength and speed both changes

so we will have

so here the frequency will remain the same

The images of clouds and trees in water are always less bright than in reality because only a portion of the incident light is reflected and quite a large portion goes mid water.

Since angle of incident = angle of reflection

Hence r = 30^o

And here angle of deviation,

δ = 180^o − (i+r)

δ = 120^o

The angle between the reflected ray and incident ray is measured w.r.t the normal.

The angle between the incident ray and reflected ray = 1/2 ​(∠i + ∠r)

It is given that the angle of incidence is 38^∘ with the surface of the normal.

So,the angle of the reflection will be 90^∘ − 38^∘ = 52^∘with the surface of normal.

CONCEPT:

• Plane Mirror: A plane mirror is a mirror with a flat (planar) reflective surface.

The characteristics of an image formed in a plane mirror:

• The image formed by the plane mirror is virtual and erect i.e. image cannot be projected or focused on a screen.
• The distance of the image ‘behind’ the mirror is the same as the distance of the object in front of the mirror.
• The size of the image formed is the same as the size of the object.
• The image is laterally inverted, i.e. left hand appears to be the right hand when seen from the plane mirror.

• If the object moves towards (or away from) the mirror at a certain rate, the image also moves towards (or away from) the mirror at the same rate.

• From the above discussion, we can say that the image formed by a plane mirror is always erect, virtual, and the same size. 

The minimum mirror height required to see our whole body in a mirror oriented in parallel to our body is half the height of our body. The top edge of the mirror should be half in-between the level of our eyes and the top of our head, and the bottom edge of the mirror should be at a level half way between our eyes and our feet. This is independent of our distance to the mirror.

Lets go option wise:

A. If the incident rays are converging, that means they are from virtual object very far away. If rays are from a real object, they will be diverging. Hence Option A is wrong. 

B. If final rays are converging, they will definitely intersect and we will have a formation of a virtual image. Hence Option B is correct. Option C & D are absurd.