# Two photons are moving in opposite directions each with a velocity of light (c). Then their relative velocity is:

1. c
2. 2c
3. c/2
4. 0.9c

## Two photons are moving in opposite directions each with a velocity of light (c). Then their relative velocity is:

Two photons are moving in opposite directions each with a velocity of light (c). Then their relative velocity is c.

## The Special Theory of Relativity:

According to relativity, the speed of light is a universal constant. Any velocity added or subtracted to the speed of light yields velocity of light.

The special theory of relativity (1905) is based on the following two postulates:

1. Laws of physics have the same form in all inertial reference frames moving with a constant velocity with respect to another.
2. The speed of light has the same value for all observers in a different inertial frame of reference.

This question is about MSc Physics, Special Theory of Relativity. This is the previous year’s question about the competitive exams.

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#### MSC Physics MCQS for all Subjects

 MSC Physics MCQs 1. Classical Mechanics 2. Quantum Mechanics 3. Electromagnetic Theory 4. Atomic Physics 5. Nuclear Physics 6. Solid State Physics 7. Electronics Physics 8. Heat and Thermodynamics 9. Mathematical Method for Physics 10. Special Theory of Relativity 11. Physical Wave Optics 12. Waves and Oscillations