Question

When it comes to EINSTEINS SPECIAL RELATIVITY, what is correct - choose one of the three alternatives each for a) - d)

a) A PHOTON (1. Has energy but no mass - 2. Has mass but no energy - 3. Has momentum but no energy)

b) A PHOTON (1. Can create massive particles - 2. Can only create mass-less particles - 3. Ages conversely proportional to its energy)

c) IS AN EXAMPLE OF AN INVARIANT (1. Momentum - 2. Energy - 3. Mass)

d) THE NUCLEAR WASTE IN A NUCLEAR POWER PLANT (1. Weighs the same as the nuclear fuel rods - 2. Weighs more than the nuclear fuel rods - 3. Weighs less than the nuclear fuel rods)

Answer 1

a)

A photon always travels at the speed of light in any inertial frame of refrence is a postulate of the EINSTEINS SPECIAL RELATIVITY. So, a photon cannot be at rest any inertial frame of refrence and thus does not have mass( rest mass to be precise). A photon ofcourse has energy E = hf, and momentum p = E/c. So, the correct option is (1).

b)

From the mass-energy equation of Einstein E = mc², which states that pure energy can be converted into mass and vice versa, a photon can create massive particles. Pair production is an example. Ofcourse, the mass of massive particles created by a photon is proportonal to the energy of the photon. So, the correct option is (1)

c)

Among the three quantities given, only the (rest) mass is invariant, i.e., has same value in all inertial frames. Momentum and energy are conserved quantities in a particular refrence frame while as rest mass is not a conserved quantity in special relativity.

So, the correct option is (3).

d)

Nuclear waste should weigh less than the nuclear fuel rods as the energy produced in the nuclear power plants comes at the expense of loss of some mass of the fuel rods as per the  mass-energy equation of Einstein E = mc².

So, the correct option is (3)