Refraction
09 September 2023 02:05
Refraction
The bending of light rays when they pass obliquely from one medium to another.
Causes of Refraction
Due to change in speed of light on going from one medium to another.
*Greater the difference in speed of light in two media, greater will be the amount of refraction.
Optically denser medium-> Low speed (Higher refractive index)
Optically rarer medium-> High speed (Lower refractive index)
When a ray of light enters a denser medium from a rarer medium, its speed reduces which
reduces its wavelength and light bends towards the normal.
When a ray of light enters a rarer medium from a denser medium, its speed will increase which
increases the wavelength and hence light bends away from the normal.
*Bending of light is directly proportional to refractive index
*The speed of light in a medium is inversely proportional to refractive index
Laws of Refraction of Light
1. Incident ray, refracted ray and normal to the surface separating two mediums, all lie in the
same plane.
2. The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for a
pair of medium.
I.e.
This constant is known as *Refractive Index* of the medium in which refracted ray travels w.r.t.
medium in which incident ray travels.
*Refractive index is represented by *n*.
This law is also known as 'Snell's Law'.
Relative Refractive Index Absolute Refractive Index
It is the measure of how much the speed of light when it foes It is defined as the ratio of speed of light in air/vacuum to the speed
from one medium to another. in given medium.
n2air = Vair/V2 = C/V2
n1air = Vair/V1= C/V1
n21 = 1/n12
Absolute Refractive Index in terms of Relative Refractive Index
n21 = v1/v2 * c/c
= v1/c * c/v2
= 1/n1 * n2
n1= c/v1
n2 = c/v2
n21 = n2/n1
n12= n1/n2
Q: W.r.t air, the refractive index of water and benzene are 1.33 and 1.5 respectively. Calculate
the refractive index of benzene w.r.t to water.
Explanation of Bending of Light
1. When light goes from rarer to denser medium,
n1 < n2 ( 1 rarer and 2 denser)
According to Snell's law,
sin i / sin r = n21
Hence, refracted ray bends towards the normal.
2. When light goes from denser to rarer medium
n1 > n2 (1 rarer and 2 denser)
According to Snell's Law,
*n2/n1=n21
Ray bends away from the normal.
3. When light goes from one medium to another having same refractive index
n1=n2
According to Snell's law,
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09 September 2023 02:05
Refraction
The bending of light rays when they pass obliquely from one medium to another.
Causes of Refraction
Due to change in speed of light on going from one medium to another.
*Greater the difference in speed of light in two media, greater will be the amount of refraction.
Optically denser medium-> Low speed (Higher refractive index)
Optically rarer medium-> High speed (Lower refractive index)
When a ray of light enters a denser medium from a rarer medium, its speed reduces which
reduces its wavelength and light bends towards the normal.
When a ray of light enters a rarer medium from a denser medium, its speed will increase which
increases the wavelength and hence light bends away from the normal.
*Bending of light is directly proportional to refractive index
*The speed of light in a medium is inversely proportional to refractive index
Laws of Refraction of Light
1. Incident ray, refracted ray and normal to the surface separating two mediums, all lie in the
same plane.
2. The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for a
pair of medium.
I.e.
This constant is known as *Refractive Index* of the medium in which refracted ray travels w.r.t.
medium in which incident ray travels.
*Refractive index is represented by *n*.
This law is also known as 'Snell's Law'.
Relative Refractive Index Absolute Refractive Index
It is the measure of how much the speed of light when it foes It is defined as the ratio of speed of light in air/vacuum to the speed
from one medium to another. in given medium.
n2air = Vair/V2 = C/V2
n1air = Vair/V1= C/V1
n21 = 1/n12
Absolute Refractive Index in terms of Relative Refractive Index
n21 = v1/v2 * c/c
= v1/c * c/v2
= 1/n1 * n2
n1= c/v1
n2 = c/v2
n21 = n2/n1
n12= n1/n2
Q: W.r.t air, the refractive index of water and benzene are 1.33 and 1.5 respectively. Calculate
the refractive index of benzene w.r.t to water.
Explanation of Bending of Light
1. When light goes from rarer to denser medium,
n1 < n2 ( 1 rarer and 2 denser)
According to Snell's law,
sin i / sin r = n21
Hence, refracted ray bends towards the normal.
2. When light goes from denser to rarer medium
n1 > n2 (1 rarer and 2 denser)
According to Snell's Law,
*n2/n1=n21
Ray bends away from the normal.
3. When light goes from one medium to another having same refractive index
n1=n2
According to Snell's law,
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