1. A wavefront is the locus of points having same phase of oscillation.
2. Rays are lines perpandicular to the wavefront, which shows the direction of propagation of energy.
3. The time taken for light to travel from one wavefront to another is same along any ray.
4. Huygen's construction is based on the principle that every point of a wavefront is the source of secondary wavefront that is the surface tangent to all secondary wavefronts gives rise to a new wavefront.
5. The law of refraction (i=r) and the Snell's law of refraction
sini /sinr =v1/v2=n2/n1 = n21
can be derived using the wave theory. Here v1 and v2 are the speed of light in media 1 and 2 wiyh refractive index n1 and n2 respectively.
6. The frequency ν remains same when light travels from one medium to another. The speed of the wave is given by
where λ is the wavelength of the wave and T is the period of oscillation.
7. Emission , absorption and scattering are the three proscesses by which matter interacts with radiation.
8. In emission , an accelerated charge radiates an looses energy.
9. In absorption the charge gains energy at the expence of the EM wave.
10. In scattering the charge accelerated by incident EM wave radiated in all direction.
11. Two sources of light are coherent if they have same frequency and stable phase difference.
12. In case of coherent sources of light the total intensity I is not just the sum of individual intensities I1 and I2 due to two sources but also includes an interference term that is
I = I1 + I2 + 2kE1.E2
where E1 and E2 are the electric fields at a point due to the sources.
13. The interference term averaged over many cycles is zero if (i) the source of light have different frequencies or (ii) the source have the same frequency but not stable phase difference. For such incoherent sources I = I1 + I2
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