Duduli

Answer:- It is a phenomenon in which their is a change in frequency of light due to relative motion between source and observer.This effect is observable only when the speed of observer is comparable to speed of light.

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Answer:- A field is said to be a conservative field if the total workdone in moving a particle between two points in that field is independent upon actual path taken and depends only in initial and final position. e.g Electric field, gravitational field

Answer:- Spherical shells are layers of a sphere at different distance from the centre.If you consider a spherical onion 🧅 it's body is made of different concentric layers.Each layer encloses the other.Each layer is a spherical shell. Hallow sphere is nothing but a thick spherical shell.In hallow sphere a small concentric solid sphere has been removed from the solid sphere.