Light and laws of Optics
Light is dual in nature. It occurs both in wave and particle form.
The light occurs in wave packets called photons, where the energy of
the photon is given by E=hf, where h is the planck's constant. This
energy is strong
enough to liberate the electon from the atom thus creating a free
electron and an ion.
The speed of light is maximum in vaccum. It is less in any medium other
than vaccum.
1. Reflection
Laws of Reflection
1. A1=A2
2. Incident Ray, Reflected Ray and Normal all lie in the same plane.
2. Refraction
Figure a. v1>v2 because refractive index, n2 > n1. Hence,
A2<A1 and refracted ray towards normal.
Figure b. v2>v1 because refractive index, n1 > n2. Hence,
A2>A1 and refracted ray away from normal.
3. Snell's law of Refraction
index of refraction, n= speed
of light in vaccum (c)
(1)
speed of light in medium
(v)
sinA2 = v2
sinA1 v1
Also, c=frequency(f) * wavelength(λ
)
v1=fλ1, v2=fλ2
λ1 = v1
λ2 v2
using (1),
λ1n1=λ2n2
for air, n=1, then n=λ
λn
n>1, λn<λ
then, n1SinA1=n2SinA2 (2)
This is the Snell's law of refraction.
4. Total Internal Reflection
n2<n1
at critical angle, Ac, A2=90°
When A1>Ac, the wave is reflected back, using (2) to find
critical angle,
n1SinAc=n2Sin90°=n2
thus, SinAc=n2
n1
Ac=Sin-1
n2
n1