Title REVISION PART 2.pdf ✅

MCQ Revision 1. All the laws of physics have the same form in all inertial reference frames. (T) True. This is a core idea of the principle of relativity, which states that the laws of physics are invariant (the same) in all inertial reference frames. 2. The speed of light in vacuum has the same value, c = 3.00 X 10^8 m/s, in all inertial frames, regardless of the velocity of the observer or the velocity of the source emitting the light. (T) True. This is a key postulate of special relativity. 3. If two events are simultaneous in one inertial frame, they are simultaneous in any other inertial frame moving with respect to the first. (F) False. This is not true in special relativity. Simultaneity is relative, so two events that are simultaneous in one frame may not be simultaneous in another frame moving relative to the first. 4. The proper length of an object is defined as the length of the object measured by someone who is moving at constant speed with respect to the object. (F) False. The proper length is the length of the object measured in the object's rest frame, i.e., by an observer who is at rest relative to the object. 5. It is impossible to accelerate a particle from rest to a speed equal to c. (T) True. According to relativity, no object with mass can reach the speed of light, as it would require infinite energy. 6. The laws of physics have the same forms in all reference systems that move uniformly with respect to one another. (T) True. This is a restatement of the principle of relativity. 7. Michelson-Morley experiment showed that Ether exists and the speed of light relative to it is 3x10^8 m/s. (F) False. The Michelson-Morley experiment showed that the speed of light is constant in all directions and independent of the motion of the observer, ruling out the existence of the "ether" as a medium for light. 8. The speed of light in vacuum, water, and oil is always measured to be 3x10^8 m/s. (F) False. The speed of light is c = 3 × 10^8 m/s in vacuum, but in other media like water and oil, light travels slower than in a vacuum. 9. The proper time is the time as measured by an observer moving at constant speed with respect to the clock. (F)
False. The proper time is the time measured by an observer who is at rest relative to the clock, i.e., the clock itself. 10. Massless particles can move with any speed up to c. (F) False. Massless particles, like photons, always move at the speed of light, c. They cannot move slower or faster. 11. Any force would be invariant under the Galilean transformation as long as it involved only the relative positions of interacting particles. (T) True. In classical mechanics (under Galilean transformations), force is invariant if only relative positions of particles are considered. 12. The rest energy of an electron or positron is 0.51 MeV; hence pair production requires a photon energy of at least 1.02 KeV. (F) False. The rest energy of an electron or positron is 0.511 MeV (not 0.51 MeV), so the total energy required for pair production is 1.022 MeV, not 1.02 KeV. 13. When two particles (for example, a proton and neutron) are bound together to form a composite (like a deuteron), part of the rest energy of the individual particles is lost, resulting in the binding energy of the system. (T) True. The binding energy of the system comes from the difference in the total energy of the bound state and the sum of the individual particles' energies. 14. As the velocity of a moving body approaches c, the acceleration caused by any finite force approaches zero. (T) True. As velocity approaches the speed of light, relativistic effects cause the acceleration to decrease, making it impossible to accelerate further with finite force. 15. The principle of relativity of Einstein's special theory is restricted to inertial motion. The relativity it asserts does not extend to accelerated motion. (F) False. While the principle of relativity applies strictly to inertial reference frames, Einstein's general theory of relativity extends the concept of relativity to accelerated frames of reference. 16. The Michelson-Morley experiment was made to prove that the speed of light was c only with respect to the Ether or a frame fixed in the Ether. (F) False. The experiment aimed to detect the motion of Earth through the supposed ether, but it found no evidence for the ether, implying that the speed of light is constant and independent of the observer's motion. 17. f_obs = f_source and λ_obs = λ_source only when the sources and observer are approaching with equal speed in opposite directions relative to Earth. (T)
True. This refers to the Doppler effect. The observed frequency and wavelength will match the source's only if the source and observer are moving towards each other with the same relative speed. 18. Changing the intensity of a monochromatic light beam will change the number of photoelectrons but not their energies. (T) True. The energy of the photoelectrons depends on the frequency of the light (via the photoelectric effect), while the intensity affects the number of emitted photoelectrons. 19. Blackbody is an ideal body that absorbs all radiation incident upon it, regardless of frequency. (T) True. A blackbody absorbs all radiation, regardless of frequency, and does not reflect or transmit any. 20. As the wavelength of the radiation decreases, the intensity of the black body radiations decreases. (F) False. According to Wien's law, as the temperature of a blackbody increases, the peak wavelength of emitted radiation decreases, but the overall intensity increases. 21. The radiations emitted by hot bodies are called X-rays. (F) False. Hot bodies generally emit thermal radiation, which can be in the infrared, visible, ultraviolet, or even X-ray regions depending on temperature, but they are not specifically X-rays unless the temperature is extremely high. 22. A black body is defined as a perfect absorber of radiations. It may or may not be a perfect emitter of radiations. (F) False. A blackbody is both a perfect absorber and a perfect emitter of radiation. 23. Electromagnetic wave theory of light could not explain Black Body radiations. (T) True. Classical electromagnetic wave theory (Rayleigh-Jeans law) predicted the "ultraviolet catastrophe," which didn't match experimental observations of blackbody radiation. This led to the development of quantum theory (Planck's law). 24. For an object other than a black body, its emissivity, e, is 1. (F) False. For a non-blackbody, the emissivity is less than 1. A blackbody has an emissivity of 1. 25. If the only change you make is to decrease the temperature of an object, the total amount of power emitted decreases in all cases. (T)
True. According to the Stefan-Boltzmann law, the power emitted by an object is proportional to the fourth power of its temperature, so decreasing temperature decreases the emitted power. 26. Investigate how the observed spectrum responds to changing temperature. If the only change you make is to decrease the temperature of an object, the amount of power emitted at 1000 nm will increase in some cases. (F) False. Decreasing the temperature of an object generally shifts the peak emission to longer wavelengths (according to Wien’s law), and reduces the intensity at any specific wavelength. 27. Sun’s radiation is similar to that of a Black Body. (T) True. The sun's radiation is approximately a blackbody spectrum, though not perfect, it's very close in shape. 28. Black surfaces are poor reflectors of heat. (T) True. Black surfaces absorb more radiation and reflect less, which is why they are poor reflectors of heat. 29. Black Body is an ideal body that absorbs all radiation incident upon it, regardless of frequency. (T) True. This is the definition of a blackbody. 30. The temperature of a black body has no effect on the distribution of emitted radiation. (F) False. The temperature of a blackbody affects both the intensity and the peak wavelength of the emitted radiation (Wien's Law and Stefan-Boltzmann Law). 31. A black body emits radiation across all wavelengths, creating a continuous spectrum. (T) True. A blackbody emits a continuous spectrum of radiation at all wavelengths. 32. The Stefan-Boltzmann Law states that the total energy radiated by a black body is directly proportional to the fourth power of its temperature. (T) True. This is a correct statement of the Stefan-Boltzmann Law. 33. Wien's Displacement Law describes the relationship between the temperature of a black body and the wavelength at which it emits the most radiation. T 34. According to classical physics, the ultraviolet catastrophe accurately predicts the behavior of black body radiation F