Chapter 16, Problem 19A

To determine

To Explain: Whether moving downhill in the gravitational field has effect on the frequency of light or not.

Explanation of Solution

Introduction:

Force due to gravity affectsevery object on the earth. According to Newton’s law of gravity, ‘every massive object exerts force of attraction on the other object’. The magnitude of the force is directly proportional to the product of the masses and inversely to the square of the distance between the object. Till 1915,it wasassumed that only a massive body is affected by the gravity. But after the Einstein’s general theory of relativity, it is said that every massive body bends the fabric like space-time curvature and other objects, even light also fall into it. Light is electromagnetic radiation with zero rest mass.

According to Einstein’s general theory of relativity, light can be affected by the strong gravity. In black hole, strong gravitational field at the center of the black hole bends the light inward. Depending on the of refractive index of the medium, when light passes from one medium to another medium, its speed changes. As the effect of gravitational field on the surface of the earth is negligible. Redshift is prominently observed in case of black hole. Redshift is observed in the electromagnetic radiation when light undergoes increase in wavelength. In case of frequency; during red shift, frequency decreases. The intense gravitational field just outside the black hole makes more effect on redshift. According to theory of relativity, when light goes downhill in the gravitational field, it decreases the frequency of light. The amount of redshift depends on the intensity of the gravity. Redshift observed in case of black hole; not in case of earth’s gravitational field.

Conclusion:

Therefore, frequency of light decreases, when moving downhill in the gravitational field. But in case of earth’s gravitational field, redshift is not observed. Bending of light isobserved in case of blackhole where gravity is very high that makes spacetime curvature.