Question

The equation \( E = pc \), where \( E \), \( p \), and \( c \) represent energy, momentum, and velocity of light, is valid:

• A. for an electron as well as for a photon
• B. for a photon but not for an electron
• C. for an electron but not for a photon
• D. neither for an electron nor for a photon

Hint:

The equation \( E = pc \) is specific to massless particles such as photons. For particles with mass like electrons, a different relativistic formula is used.

Answer 1

The Correct Option is B

Step 1: Understanding the equation.
The equation \( E = pc \) is a relativistic equation that is valid for massless particles like photons. For an electron, the equation \( E = pc \) does not hold true because electrons have mass.

Step 2: Analysis of options.
- ( For an electron as well as for a photon: This is incorrect because \( E = pc \) is not valid for an electron.
- ( For a photon but not for an electron: This is correct because the equation is valid for photons, but not for electrons.
- ( For an electron but not for a photon: This is incorrect because the equation is not valid for electrons.
- ( Neither for an electron nor for a photon: This is incorrect because it is valid for photons.

Step 3: Conclusion.
The correct answer is ( for a photon but not for an electron.