Why are two bulbs lighting the same walls considered incoherent sources? How do their intensities add up?

Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another set of three bulbs of the same wattage are connected in parallel to the source. Will the bulb in the two circuits glow with the same brightness? Justify your answer.

What are coherent sources of light? Why no interference pattern is observed when two coherent sources are very for apart?

State with reason, why two independent sources of light cannot be considered on coherent sources.

If amplitudes of two lights from coherent sources in Young.s double slit experiment are in the ratio 2:5, then finf the ratio of intensity at the maxima to the intensity at minima in interference pattern.

Doppler's effect in sound is different depending on whether the source or observer is in motion. However in case of light, the Doppler's shift is the same irrespective of whether the source or observer is in motion, explain how?

Two polaroids A and B are kept in crossed poisiton.How should a third polariod C be placed between them so that the intensity of polarised ligth transmitted by polaroid B reduces to 1//8th of the intensity of unpolarised light incident on A?

What will be the intensities of the maxima and minima,when the ligth waves interfering with each other are of the same amplitude?Show that the intensity of the maxima is four times the intensity of light due to each of two slits.

The figure shows the stopping potential for the phototelectron versus (1/lambda) graph for two metals A and B, lambda being the wavelength of incident light If the distance between the light source and the surface of metal A is increased, how will the stopping potentail for the electrons emitted from it be affected? justify your answer.

A toaster produces more heat than a light bulb, when connected in parallel across a source of e.m.f. Which has greater resistace and why?