A project on wave nature of light

By:Manisha Xii – scienceFaith Academy2008-09

Wave nature of lightWave nature of light• Light is an

electromagnetic wave.

• EM waves are those waves in which there are sinusoidal variation of electric and magnetic fields at right angles to each other as well as to the direction of propagation of wave.

The Wave Nature of Light

Wavelength &Frequencyc = λ ν

Diffraction and

Interference

• Two phenomenon explaining wave nature of light.

• Diffraction and interference are similar phenomena.

• Interference is the effect of superposition of 2 coherent waves.

• Diffraction is the superposition of many coherent waves

Huygens’ principle

• Every point on the given wave front acts a fresh source of new disturbance called secondary wavelets which travel in all directions.

• A surface touching these secondary wavelets, tangentially in the forward direction at any instant gives the direction of the new wave front.

Huygen’s Picture of a Plane wave

Huygen’s Explanation of Reflection

Huygen’s Explanation of Refraction

Young’s double slit experiment: classic wave effect

Young’s double slit experiment

Interference of light is the phenomenon of redistribution of light energy in a medium on account of superposition of light waves from two coherent sources

Formation of crests n troughs

Double slit experiment with particles (e.g. electrons)

Interference pattern with one slit blocked

Double slit experiment with particles (e.g. electrons)

Interference pattern observed on the screen

When both the slits are open

• If the crests of one wave coincide with the crests of the other, the amplitudes of the waves are additive. Thus, if the amplitudes of both waves are equal, the resultant amplitude is doubled .

If the crests of one wave coincide with the troughs of the other wave, the resultant amplitude is decreased. This destructive interference is accompanied by a decrease in light intensity.

Magical effects of interference

• When a film of oil floating atop a body of water reflects light, a swirling mass of colors seems to magically appear. The cause of this strange phenomenon is interference between light waves.

Diffraction

When light waves hit an obstacle it bends around the edges of the obstacle.

• This property of bending of light is called diffraction.

• For example, if light of red wavelength from a laser source hits a small hole, it bends around the edges of the hole and forms a pattern called an Airy disc pattern.

Single slit diffraction

• Diffraction occurs on account of mutual interference of secondary wavelets starting from the portions of wave front which are allowed to pass from the aperture.

The pattern spreads out due toDiffraction.

Wave pictureLight spreads out when passedthrough small aperture.

Position of minima:

a sin θ n= nλPosition of maxima

a sin θ n= (2n+1)λ/2

If unpolarized light is incident on1 polarizer, the intensity of thelight passing through is I= ½ I0.

Polarization

• Light scattered at90 degrees is 100% polarized.

Polarization &Scattering

Law of malus• If the incident wave

is already polarized, then the transmitted intensity is I=I0cos2q where q is the angle between the incident wave’s direction of polarization and the transmission axis of the polarizer.

A polarizer will transmit linear polarized waves in the samedirection independent of the incoming wave.

Brewster's Law • when the light is

incident at a particular incident angle, called the Brewster angle ip, on an interface separating air from a medium of refractive index ‘n’ then the reflected light is fully polarized.n = tan ip

light :a wave leading to our future

The end