Special Theory Of Relativity MSQ Level – 2 - Physics MCQ

From the rest frame of the ground observer the clock in the train is moving. The train clock runs slow from the point of view of the ground observer. From the rest frame of the train observer, the ground clock appears to be moving
∴ From the reference frame of the train, the ground clock runs slow

The correct answers are: The ground observer finds the train clock run slow., The train observer finds the ground clock run slow.

Correct Answer :- a,d

Explanation : b) mass of a photon is due to its momentum. When photon comes to rest velocity becomes zero thus mv=p=0. Hence rest mass of a photon is zero.

c) Rest mass (m0) is defined as the mass of the object at rest (or in rest frame) which remains constant.

Only the mass of the moving object changes as the speed increases  via m = m0/(1 - v²/c²)^1/2

It is possible that neither obeys special theory of relativity but they can obey under some conditions.

In physics, the Lorentz transformations are a one-parameter family of linear transformations from a coordinate frame in spacetime to another frame that moves at a constant velocity (the parameter) relative to the former. The respective inverse transformation is then parametrized by the negative of this velocity. 


In the transformation for x  and  t,  the coefficient of x  and  t,  is the same!
The correct answer is:

Light Emitting Diode (LED) is an example of PN junction diode. A layer of Phosphor is added at the junction who is responsible for the glow. Phosphor is a substance that exhibits the phenomenon of luminescence.

S₁ is at rest
∴  lifetime is least in this frame  

The correct answers are: 

The two postulates are:
The laws of physics are the same and can be stated in their simplest form in all inertial frames of reference.
The speed of light c is a constant, independent of the relative motion of the source.

To clarify the doubt:
The speed of light is a constant c = 3.00 × 10⁸ m/s in a vacuum. If you remember the effect of the index of refraction from The Law of Refraction, the speed of light is lower in matter.

One of the postulates of Einstein’s Special Theory of Relativity states that all the inertial frames are equivalent to the formulation of laws of physics. Thus, it is suitable for all the inertial frames.

Particles traveling at speeds close to the speed of light disintegrate slower than when they are at rest” is more apt when compared to “The life time of particles is greater when they are moving at speeds comparable to c

Rocket runs slow so earth clock reads

 

∴  Earth clock read 1 hr 15 minutes.

By the earth observer, the rocket is now at a distance of   hours away.
∴ 

light signal will take 3/4 hour to return to earth.

Since, the signal left 5/4 hr after the departure

∴  light signal reaches 5/4 + 3/4 = 2hrs later.

Earth clock runs slow (in the reference frame of the rocket)

The correct answers are: According to the earth clock the signal was sent at 75 minutes after departure of the rocket, According to the rocket observer the signal reached earth 150 minutes after the rocket left., According to the earth clock, the signal reached earth 120 minutes after the rocket’s departure