Refraction of Light

Flashcards based on lecture notes about light refraction, optical density, and related phenomena.

What is the speed of light in a vacuum?

3 x 10^8 m/s

What happens to the speed of light as it moves from vacuum to air, glass and diamond?

It decreases

Define optical density.

The extent by which the speed of light decreases in a medium.

Which is optically the most dense: diamond, air, or vacuum?

Diamond

Which is optically the rarest: diamond, air, or vacuum?

Air or vacuum

Is mass density related to optical density?

No, kerosene has lower mass density than water but higher optical density.

What is refraction?

Change in the path of a ray of light when it travels from one medium to another with a different optical density due to sudden change of speed.

Define rarer medium in terms of the speed of light

A medium where the speed of light is greater than in another medium. Air or vacuum is considered optically the rarest medium.

Define denser medium in terms of the speed of light

A medium where the speed of light is less than in another medium. Optic fiber and diamond are examples of optically densest mediums.

Define Interface in the context of refraction.

Junction of two optical media

Define point of incidence.

Point on which the ray is incident

Define normal.

Perpendicular to interface at point of incidence

Define incident ray.

A ray that strikes on the interface

Define refracted ray.

A ray that travels in other medium

Define angle of incidence.

Angle made by incident ray with normal

Define angle of refraction.

Angle included by normal and refracted ray

State the laws of refraction.

1) Incident ray, normal, and refracted ray are on one plane. 2) Snell's Law.

State Snell's Law equation.

μ1 / μ2 = sin(i) / sin(r), where medium 1 is the medium of ray of incidence.

What is the equation for angle of deviation when light travels from rarer to denser medium?

δ = i - r

What is the equation for angle of deviation when light travels from denser to rarer medium?

δ = r - i

Under what two conditions will there be no deviation of a light ray?

a) Optical densities of both media are equal. b) Incident ray is perpendicular to the interface (i = zero).

What property of light changes during refraction, and what remains constant?

Speed and wavelength change, frequency does not change.

Define refractive index.

Ratio of speed of light in medium 1 to the speed of light in medium 2. Also the ratio of wavelengths.

What is absolute refractive index.

If the first medium is vacuum or air the refractive index is called absolute refractive index.

The absolute refractive index is always greater than what value?

1

How does temperature affect refractive index?

As temperature increases, refractive index decreases.

How does wavelength affect refractive index?

As wavelength increases, refractive index decreases.

Which color deviates more, violet or red?

Violet, because it has a smaller wavelength.

Define Lateral Displacement.

The perpendicular distance between the incident ray and emergent ray when light is incident obliquely on a rectangular glass slab.

What factors does lateral displacement depend upon?

Refractive index, thickness of glass slab, and angle of incidence.

How does temperature affect lateral displacement?

As temperature increases, refractive index reduces, and hence lateral displacement reduces.

How does wavelength affect lateral displacement?

Greater wavelength, lesser the refractive index, hence Lateral displacement reduces.

In a thick mirror, which image is the brightest?

The second image formed.

What are the components of a right triangular prism?

Triangle as base and top, and rectangular surfaces on each edge.

Define refracting edge of prism.

The edge where refraction occurs.

What is the angle of deviation in a prism?

Angle formed between incident and emergent ray.

What occurs when the angle of incidence equals the angle of emergence in a prism?

The angle of deviation is minimum (δmin), also refracted ray is parallel to base and i1=i2

What happens to a ray of light incident obliquely on a glass prism?

It suffers deviation at every surface and always bends towards the base.

How does refractive index affect the angle of deviation?

More the refractive index, more the deviation.

How does temperature affect the angle of deviation?

As the temperature of the medium increases, the speed increases, hence less refractive index and deviation reduces.

How will the color of light modify the angle of deviation?

Violet has smaller wavelengths, so it will deviate more than red.

How does the angle of the prism affect the angle of deviation?

Greater the angle of prism, greater the angle of deviation.

How does the angle of incidence affect the angle of deviation in the prism?

As angle of incidence increases, the angle of deviation decreases to a minimum value and then starts increasing.

Why does a stick underwater appear bent?

Refraction of light causes objects in denser media to appear raised.

Define real depth and apparent depth.

Real depth is the actual depth, apparent depth is the perceived depth due to refraction.

What does the shift due to refraction depend upon?

Refractive index and depth/thickness of medium.

How does temperature affect the object shift?

More temperature of medium, the less refractive index, so less shift.

How does wavelength affect the object shift?

More wavelength, less refractive index, so more shift. Red has less shift than violet.

Why do stars appear to twinkle?

Due to changing refractive index of air in the atmosphere.

When fishing, why should one aim for the tail of the fish?

Due to refraction, the fish appears raised.

Why is sunrise visible a few minutes before the actual sunrise?

Due to refraction of light in the atmosphere.

What are the conditions for total internal reflection?

1. Light travels from denser to rarer medium. 2. Angle of incidence in denser medium is greater than critical angle.

Define critical angle.

Angle of incidence in denser medium for which angle of refraction in rarer medium is 90 degrees.

What is the relationship between critical angle and refractive index?

Sin(ic) = 1 / μwater = Cosec ic

How does material affect critical angle?

For diamond, refractive index is high, so critical angle is less.

How does temperature affect critical angle?

If temperature of medium increases, speed increases, then refractive index reduces hence critical angle increases.

How does wavelength affect critical angle?

More wavelength, critical angle is bigger.

What is total internal reflection?

If a ray of light travels from denser medium to rarer medium such that the angle of incidence in denser medium is greater than the critical angle, the ray of light does not emerge in rarer medium, instead reflects back in denser medium

What are some applications of total internal reflection?

Periscopes, binoculars, slide projectors, empty test tube shines like mirror, crack in glass shines as mirror, diamond sparkles, mirage, and fiber optics.

Why does diamond sparkle?

Diamond is polished in a particular way, and the critical angle of diamond is very low. Since ray enters, it suffuses total internal reflection. Emerges at particular angle; hence it sparkles.

What causes a mirage?

Layer of air is warmest so it is in contact with soil and is optically rarer. Ray of light passes from denser to rarer medium and at one particular point is totally internally reflected.

How does fiber optic work?

Fiber optic has a core made of material with a very high refractive index. Hence, its critical angle is very low. Once the ray of light enters into it, it keeps getting internally reflected.