Physics [3 Mark Question Answer]

Let Real depth = x

∵ Refracture Index, μ = `"Real depth"/"Apparent depth"`

⇒ `4/3="x"/("x"-4)`

⇒ 4x − 16 = 3x

∴ x = 16 cm.

∵ According to Snell's law of refraction:

n = `sin"i"/sin"r"`

`3/2=(sin45°)/sin"r"`

⇒ `3/2=(1//sqrt2)/sin"r"`

sin r = `2/(3sqrt2)`

= `sqrt2/3`

In the case of powdered glass, irregular reflection takes place from various particles. Thus, light is sent back into the same medium. Therefore, it looks opaque. On putting water over the powder incident light gets refracted through water. That is why it looks transparent.

Critical angle for water is 49°. The rays of light entering the water from below, suffer refraction. If these rays strike the water-air surface at an angle which is greater than 48°, they get totally internally reflected. These rays on emerging out of the water, appear to come from the upper surface of the water, which in turn appears silvery.

This is because in total internal reflection 100% of incident light gets reflected. On the other hand, in ordinary reflection, 20% to 30% of incident light is lost. So, images formed in the first case are brighter than the images formed in the second case.

The angle of deviation produced by a prism increases with the decrease in wavelength of the light used.
(i) Violet light is deviated most by a prism.
(ii) Red light is deviated least by a prism.

A prism is said to be in the position of minimum deviation when the angle of incidence of the light ray at the first prism surface is equal to the angle of emergence at the second surface of the prism.
In this condition, the refracted ray inside the prism is parallel to the base of the prism (if the prism is equilateral).

(i) A total reflecting prism can deviate the path of a ray of light by 90°.
(ii) A total reflecting prism can turn a ray of light through 180°.
(iii) A total reflecting prism can invert the rays of light.

Due to refraction, when the rays travel from water to air, the apparent image of the fish is formed at a higher level and ahead of the actual position of fish. Thus, when the fisherman aims at the tail of the apparent image of fish, his spear hits the head of actual fish.

When a ray of light travels from medium I to medium II without any change of direction, it is possible under either of the following two conditions:
(i) A ray of light is incident normally on the surface separating two media.
(ii) The refractive index of the medium I is equal to the refractive index of medium II.

If light travels from air into another denser medium, the refractive index ‘μ’ of the medium.

`μ="Sine of the angle of incidence in air"/"Sine of the angle of refraction in the denser medium"`

`μ=sin i/sin r`

The refractive index ‘μ’ of an optical medium is defined as the ratio between the velocity of light in vacuum divided by the velocity of light in the given optical medium. Thus,

`µ="Velocity of light in vacuum"/"Velocity of light in the given optical medium"`

The rays coming from the face of the person, sitting across the campfire, suffer refraction on passing through hot air. Thus, we see the apparent image of the person. Since hot air is in motion, therefore its optical density changes, which in turn shifts the image rapidly. This rapidly shifting image gives a shimmering effect.

Since there is no refraction of light at the boundaries of the glass block, it is possible only when the speed of light through the liquid as well as through the block is the same. Hence the ratio between the speed of light through the liquid to the speed of light through glass must be 1 (one).

The angle of deviation depends upon:
(i) The refracting angle of prism.
(ii) The material of the prism.
(iii) The colour of light.
(iv) The angle of incidence.

The image of all the letters of the word VIBGYOR in their corresponding colours will not be at the same place. In the glass, red colour has the higher speed than violet colour, so red will be raised to the maximum while violet will be at the bottom and the other colours will be raised in the order I-B-G-Y and orange.

Yes, light can be piped from one end to the other with little loss by allowing it to enter one end of a rod of transparent material. The light will undergo total internal reflection at the wall of the rod and will proceed along its axis. This actually being achieved by using a bundle of glass fibers.

This is because a light ray coming from the fish inside the water when suffers refraction at the water-air interface, it bends away from the normal at the point of incidence. The refracted ray appears to be coming from a point at a depth less than the actual depth of the fish. That is why the fish seems to be nearer than it really is.

According to the principle of reversibility, the path of a light ray is reversible.
For e.g. if light travels from air to water along a certain path, then if the path is reversed while travelling from water to air, it will follow exactly the same path.

When total internal reflection occurs from a prism, the entire incident light (100%) is reflected back into the denser medium. Whereas in ordinary reflection from a plane mirror, some light is refracted and absorbed so the reflection is partial.

AB = Apparent depth
AC = Real depth

First, the angle of deviation produced by prism decreases with the increasing angle of incidence but on further increasing the angle of incidence the angle of deviation increases. The figure given inside shows the graph for variation of the angle of deviation with the angle of incidence.

The completed ray diagram is shown in the figure.
Following two principles are used to complete the diagram:
(1) A ray of light incident normally on the interface of two media passes undeviated.
(2) A ray of light striking the interface of two media (glass and air) from glass, at an angle of incidence, equal to 45° (which is greater than the critical angle = 42°) suffers total internal reflection.

The figure shows a prism, in which BEFC is the refracting edge, and ∠BAC or ∠EDF is the refracting angle of the prism which has been marked by the symbol A.

Since there is no refraction of light at the boundaries of the glass block, it is possible only when the speed of light through the liquid as well as through the block is the same. Hence the ratio between the speed of light through the liquid to the speed of light through glass must be 1 (one).

(a) The speed of light, travelling from liquid to glass, slow down.

(b) Speed in liquids = `"Speed of light of air"/"Refractive index of liquid"=(3xx10^8)/"Refractive index of liquid"`

Speed of light in glass = `"Speed of light in air"/"Refractive index of glass"=(3xx10^8)/"Refractive index of glass"`

Since the refractive index in glass is usually higher than that of liquid, hence the speed of light in glass will be less.

(i) Critical angle
(ii)

(iii) Total internal reflection of light.

(i)

(ii) Angle of deviation of the ray = 180°.
(iii) Prism Binoculars.