Astronomy Chapter 24 PDF

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Solved MCQ's for chapter 24...

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ASTRONOMY CHAPTER 24 1) Suppose that an object is moving and it is emitting light toward you, in vacuum. What would you notice about the light you observe? ANS:

2). What is the meaning of the word spacetime? ANS: It is the combined treatment of space and time in the theory of relativity

3) According to Special Relativity, spacecraft that would travel faster than the speed of light are ANS impossible, because nothing can travel that fast.

4) Why can an object with a nonzero mass never travel as fast as the speed of light? ANS: It would take an infinite amount of energy to accelerate it to a speed of c.

5) When do the predictions of Special Relativity match those of Newtonian physics? ANS: when objects are moving slowly

6) __________ is the result of mass distorting the fabric of spacetime. ANS: Gravity

7) Gravitational lensing occurs when _____________ distorts the fabric of spacetime. ANS: any massive object

8) The bending of light paths near a massive object is the essence of ANS: gravitational lensing.

9) General relativity predicts that coalescing (merging) massive objects would trigger ANS: . gravitational waves.

10) How does relativity compare with Newtonian physics? ANS: Relativity gives the same result as Newtonian physics when objects are moving slowly

11) Photons have no mass, and Einstein’s theory of general relativity says ANS: their paths through spacetime are curved in the presence of a massive body.

12) The gravitational redshift of light should be smallest for light emitted from the surface of ANS: a planet like the Earth.

13) According to the theory of relativity, a clock on top of Mount Everest would run _______ compared with a clock at sea level because _________________________________ . ANS: faster; of the high altitude, which means a slightly weaker gravity

14) Compared with a clock on the surface of the Earth, a clock on the International Space Station runs ANS: at approximately the same rate, but slightly slower.

15) Light is increasingly redshifted near a black hole because ANS: time is moving increasingly slower as viewed from the observer’s frame of reference.

16) The event horizon of a black hole is defined as ANS: the radius at which the escape speed from the black hole equals the speed of light.

17) What is the significance of the Schwarzschild radius around a black hole? ANS: . It is the radius at which the escape velocity equals the speed of light.

18) Hawking radiation from black holes refers to ANS: the radiation of particles created near the event horizon

19) . If the Sun suddenly turned into a black hole, what would be the radius of its event horizon? ANS: 3 km

20) A person would experience __________ as he or she approached the event horizon of a black hole. ANS: extremely strong tidal forces

21) Hawking radiation is emitted by a black hole when ANS: a virtual pair of particles is created near the event horizon.

22) If the Sun were to be instantly replaced by a 1 M  black hole, the gravitational pull of the black hole on Earth would be ANS: the same as it is now

23) . Even if a black hole emitted no light, we can still detect it ANS: . by looking for dark patches on the sky where the black hole swallows background light.

24) A red giant star is found to be orbiting an unseen object with a short orbital period. By measuring the speed at which it orbits, astronomers deduce that the unseen object has a mass of 10 M . This object is probably a ______________ because __________________________. ANS: black hole; its mass is too large to be a neutron star or a white dwarf

25) Black holes that are stellar remnants can be found by searching for ANS: variable X-ray sources.

26) What does singularity mean in the context of black holes? ANS) In the center of a black hole is a gravitational singularity, a one-dimensional point which contains a huge mass in an infinitely small space, where density and gravity become infinite and space-time curves infinitely, and where the laws of physics as we know them cease to operate. 27) What is the difference between the singularity and the event horizon of a black hole? ANS: The singularity is the centre of a black hole. A black hole by definition is a region of space with a very strong gravitational field where even light cannot escape past a certain point, called the event horizon or "the point of no return....