Refraction of Light at Plane Surfaces Flashcards
Define reflection of light.
The return of light in the same medium after striking a polished surface is called reflection of light.
Which 2 laws does reflection of light obey?
- The angle of incidence = angle of reflection
2. The incident ray, the normal, and the reflected ray all lie in one plane.
Light has the maximum speed in which medium? What is the speed?
Light has the maximum speed (=3*10^8 m s-1) in vacuum and it travels with different speeds in different media.
What is the speed of light in air?
3*10^8 m s-1
What is the speed of light in water?
2.25*10^8 m s-1
What is the speed of light in glass?
2*10^8 m s-1
When does the speed of light remain constant?
In a transparent homogeneous medium
When is a medium said to be optically denser?
When light passes from one medium to another and it slows down, the second medium is said to be optically denser than the first one. Similarly, if light speeds up in the second medium, it is said to be optically rarer than the first one.
What is the relation between optical density and density of a medium?
Optical density has no relation with the density of a medium. Optical density depends upon the speed of light in that medium, whereas the density of a medium depends on its inter-molecular separation.
Give an example of optical density not being dependent upon density.
Kerosene has a lesser density than water (as it floats on water), but it is optically denser than water.
What is reflected light?
When a ray of light travelling in a transparent medium strikes obliquely at the surface of another transparent medium, a part of light returns back into the first medium obeying the laws of reflection and is called the reflected light.
What is refracted light?
After reflection, the remaining part of light enters into the other medium and travels in a straight path but in a direction different from its initial direction and is called the refracted light.
At the boundary separating two media, light suffers __ and __
partial reflection , partial refraction
What is refraction?
The change in the direction of the path of light, when it passes from one transparent medium to another transparent medium, is called refraction.
What type of phenomenon is refraction?
The refraction of light is essentially a surface phenomenon.
What happens to the amplitude of the refracted light after reflection?
The amplitude (or intensity) of the refracted light will be less than that of the incident light because a part of the incident light has suffered reflection.
When does a ray of light bend towards the normal?
When it is travelling from an optically rarer to an optically denser medium.
What is the deviation for a ray of light travelling from a rarer to a denser medium?
i-r, because /_ r < /_ i
Define deviation.
Deviation means the angle through which the ray turns i.e., the angle between the direction of refracted ray and the direction of incident ray. It is denoted by the letter
When does a ray bend away from the normal?
When it travels from an optically denser to an optically rarer medium. The deviation is r-i
When does a ray of light pass undeviated?
When the ray of light is incident normally on the surface separating the two media. Deviation is 0.
What is the cause of refraction?
When a ray of light passes from one medium to another medium, refraction occurs because of the change in speed of light in going from one medium to another.
In which two cases does a ray of light pass undeviated from one medium to another?
- If the speed of light remains the same in passing from one medium to another.
- If the ray of light is incident normally on the surface of the second medium, its speed will change but direction will not.
Which scientist gave the two laws of refraction?
The Dutch scientist Willebrod Snell gave the laws of refraction, so they are known as Snell’s laws.
What are the 2 laws of refraction?
- The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane.
- The ratio of the sine of the angle of incidence i to the sine of angle of refraction r is constant for the pair of given media, i.e., mathematically,
sin i/sin r= constant 1μ2
sin i/sin r= constant 1μ2. Here, what is the refractive index?
The constant 1μ2 is called the refractive index of the second medium with respect to the first medium.
Which is the symbol used for RI?
The Greek letter μ (mew) is the symbol used.
Define refractive index.
The refractive index of second medium with respect to the first medium is defined as the ratio of sine of angle of incidence in the first medium to the sine of angle of refraction in the second medium.
Does RI have a unit?
RI does not have a unit as it is the ratio of two similar qualities.
What is the effect on speed due to refraction of light?
When a ray o light gets refracted from a rarer to a denser medium, the speed of light decreases; while if it is refracted from a denser to a rarer medium, the speed of light increases.
What is the effect on frequency due to refraction of light?
The frequency of light depends upon the source of light, so it doesn’t change on refraction.
What is the effect on wavelength due to refraction of light?
When light passes from a rarer to a denser medium, the wavelength decreases (since speed of light decreases, but frequency remains unchanged). When light passes from a denser to a rarer medium, wavelength increase as speed of light increases.
What is the relation between the speed of light and the frequency and wavelength?
V=f λ
What is the speed of light on air denoted by?
c
Define absolute refractive index.
The refractive index of a medium is generally defined with respect to vacuum or air, and is called the absolute refractive index of the medium.
What is the absolute refractive index of a medium denoted by?
μ
Give a second definition of refractive index
It is defined as the ratio of the speed of light in vacuum or air to the speed of light in that medium.
What is the refractive index of a transparent medium?
It is always greater than 1
Why is the refractive index of a transparent medium always greater than 1?
The speed of light in vacuum is greater than it is in any other medium (c>V)
The refractive index of diamond is 2.41. Explain the meaning of the statement
Light travels in air 2.41 times faster than in diamond
What is the refractive index of water?
1.33
What is the refractive index of kerosene?
1.41
Name the two substances that have the same refractive index
Ether and Spirit - 1.36
Glycerine and Turpentine Oil - 1.47
Give the refractive index of ordinary glass
1.5
Give the refractive index of crown glass
1.53
Give the refractive index of flint glass
1.65
Give the conditions for a ray of light to pass undeviated on refraction
- When the angle of incidence at the boundary of two media is zero
- When the refractive index of medium 2 is the same as medium 2
What happens to the frequency of light on refraction?
It remains the same
Give the formula for the relationship between wavelength in the two medium
In air, f = c/λ. In medium, f = V/λ’
c/λ = V/λ’ or λ’ = Vλ/c
c/V = μ
∴ λ’ = λ/μ
Name the factors affecting the refractive index of a medium
- Nature of the medium
- Physical condition such as temperature
- The colour or wavelength of light
How is the refractive index of the medium related to the nature of the medium?
Less the speed of light in a medium as compared to that in air, more is the refractive index of the medium
How is the physical condition related to the refractive index of a medium?
With the increase in temperature, the refractive index of the medium decreases. So, the speed of light in the medium increases.
How does the refractive index change with change in colour or wavelength of light?
In a given medium, the speed of red light is maximum and that of violet light is least, therefore the refractive index of that medium is maximum for violet light and least for red light. The refractive index of a medium decreases with the increase in wavelength.
Comment on the speed of light in air vs in other mediums (colors)
The speed of light is the same in air, but in any other transparent medium, the speed of light is different for different colors
What is the trend in the wavelength of visible light?
The wavelength of visible light increases from the violet to the red end
What does the principle of reversibility of the path of light state?
The path of a light ray is reversible
If the RI of glass with respect to air is 3/2, the refractive index of air with respect to glass is 2/3. Which principle proves this?
The principle of reversibility of the path of light
Give the formula for the principle of reversibility of the path of light
1μ2 * 2μ1 = 1
Why, in a rectangular glass block, is the emergent ray parallel to the incident ray?
- Due to refraction of light at two parallel surfaces of a parallel-sided glass block
- By the principle of reversibility of the path of light
What is lateral displacement?
The perpendicular distance between the path of the emergent ray and the direction of the incident ray is lateral displacement
Name the factors the lateral displacement depends upon
- Thickness of the block (or medium)
- The angle of incidence
- The refractive index of the block
- And therefore, on the wavelength of the light used
How does the lateral displacement depend on the thickness of the medium?
The lateral displacement increases with increase in the thickness of the medium
How does the lateral displacement depend on the angle of incidence?
More the angle of incidence, more the lateral displacement
How does the lateral displacement depend on the refractive index?
More the refractive index of the medium, more is the lateral displacement
How does the lateral displacement depend on the wavelength?
Lateral displacement increases with the decrease in wavelength of light
For what is lateral displacement more - violet light or red light?
More for violet light than red light
Give the formula for lateral displacement x
x = t sin (i-r)/cos r
