Physics MCQs
Topic Notes: Physics
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
1
What length does an observer measure for a meter stick when moving parallel to it at relativistic speeds?
Answer:
less than one meter
According to the special theory of relativity, length contraction occurs for objects moving at relativistic speeds relative to an observer. The length measured in the direction of motion is given by L = L0 * sqrt(1 - v^2/c^2). Since the Lorentz factor is less than one, the observed length is always shorter than the proper length, resulting in a measurement of less than one meter.
2
How does the passage of time change for an observer relative to a moving frame of reference?
Answer:
Dilates
According to Einstein's Special Theory of Relativity, time dilation occurs when an observer is in a frame of reference moving at a significant fraction of the speed of light relative to another frame. In such cases, time is measured to pass more slowly in the moving frame compared to the stationary observer's frame. This effect is a well-verified consequence of the constancy of the speed of light in all inertial frames.
3
How does the length of a meter stick appear to an observer moving at a relativistic speed parallel to the stick's orientation?
Answer:
less than one meter
According to the Lorentz transformation in special relativity, objects moving at relativistic speeds relative to an observer undergo length contraction in the direction of motion. Therefore, a meter stick moving parallel to an observer will appear to have a length shorter than one meter, a phenomenon known as length contraction.
4
A spacecraft travels away from Earth at 0.2c. If a light source on the ship appears blue to the passengers, what color would it appear to a stationary observer on Earth?
Answer:
Yellow
This phenomenon is explained by the relativistic Doppler effect. As the light source moves away from the observer on Earth, the light waves are stretched, resulting in a redshift. The frequency decreases and the wavelength increases, shifting the perceived color from blue toward the red end of the spectrum, appearing as yellow to the observer.
5
How does time change relative to an observer and a frame of reference moving at high speeds?
Answer:
Dilates
According to the Special Theory of Relativity, time dilation occurs when an observer measures time in a frame of reference that is moving relative to them. As the relative velocity approaches the speed of light, the time interval measured in the moving frame appears longer (dilated) compared to the time interval measured in the observer's stationary frame of reference.