PHYSICS 1020 - Spring 1997

SOLUTION TO FOURTH EXAM

31 March 1997

(Correct solution is indicated by ``(*)'')

1. The speed of electromagnetic waves calculated from Maxwell's equations is the same as the speed of light in vacuum.

   (a)(*) True (b) False

2. The speed of light depends on the relative motion of reference frame, source, medium, and observer.

   (a) True (b)(*) False

3. The observed frequency of light is always the same as that of the light emitted by the source, independently of the relative motion of light source and observer.

   (a) True (b)(*) False

4. The laws of physics are the same in all inertial frames.

   (a)(*) True (b) False

5. Any system (frame) moving with uniform velocity relative to an inertial frame is also an inertial frame.

   (a)(*) True (b) False

6. Kristin claims that, by precise measurements performed entirely inside her laboratory, she has determined that the absolute speed of her laboratory is 28 km/s. Do you think she is right?

   (a) Yes (b)(*) No

7. In the SI system of units, the meter is defined in terms of the speed of light.

   (a)(*) True (b) False

8. By measuring the speed of light in different directions with respect to the direction of motions of the Earth, Michelson and Morely provided evidence for the effects due to ``ether wind", thus proving the existence of the ether as the medium in which light propagates.

   (a) True (b)(*) False

9. Your friend Jane is moving past you at high speed. She thinks that your clock goes much slower than hers, but she is wrong. In reality, since she is moving, it is Jane's clock which goes slower than yours.

   (a) True (b)(*) False

10. Apart from small deviations dictated by allowed air-corridors, airplanes travel along great circles because these are the geodesic lines on the surface of the earth.

    (a)(*) True (b) False

11. When light travels close to a massive object, its path is bent due to gravity. This effect was first observed during a solar eclipse in 1919.

    (a)(*) True (b) False

12. The principle of the constancy of the speed of light applies only to visible light; since they have a different frequency, the speed of UV-light and microwaves can be different depending on the motion of the source.

    (a) True (b)(*) False

13. Two events, remote from each other, which are observed to happen simultaneously by one observer are in general observed to occur at different times by another observer who is in motion relative to the first one.

    (a)(*) True (b) False

14. If the speed of light were infinite, all observers would agree on the simultaneity of two events, even for events happening at different locations.

    (a)(*) True (b) False

15. The redshift observed in the light coming to us from distant galaxies is evidence for the expansion of the universe.

    (a)(*) True (b) False

16. When a very massive star has used up all its fuel, the gravitational force is no longer balanced by radiation pressure; the ensuing gravitational collapse of the star can lead to the formation of a black hole.

    (a)(*) True (b) False

17. All phenomena involving light can be explained by its wave nature.

    (a) True (b)(*) False

18. In some aspects, electrons behave like waves.

    (a)(*) True (b) False

19. Standing waves on a string are generated by the superposition of two waves travelling in opposite directions.

    (a)(*) True (b) False

20. The spectrum of thermal radiation emitted by a black body can be predicted correctly (i.e. in agreement with experiment) by using Maxwell's equations and classical thermodynamics.

    (a) True (b)(*) False

21. The photoelectric effect can be explained by assuming that light is not a continuous stream of electromagnetic radiation, but rather consists of wave packets of finite length and well-defined energy (photons).

    (a)(*) True (b) False

22. The ``Big Bang" is the loud noise due to the explosion of a nuclear bomb.

    (a) True (b)(*) False

23. Ice cubes are so efficient in cooling your drink because of water's big latent heat of fusion (i.e. it requires a lot of energy to melt ice).

    (a)(*) True (b) False

24. Water is a liquid at ``normal'' temperatures because of the polar nature of its molecules which makes them stick together.

    (a)(*) True (b) False

25. Noble gases like argon and krypton are chemically very active and form many compounds.

    (a) True (b)(*) False

26. Halogens like chlorine and fluorine are nearly inert and do not react readily with other elements.

    (a) True (b)(*) False

27. The orbital angular momentum of an electron in an atom can have any value.

    (a) True (b)(*) False

28. The electron is a member of the class of particles called ``fermions.''

    (a)(*) True (b) False

29. Some atoms are particularly stable because all electrons are in the same low energy state.

    (a) True (b)(*) False

30. The two electrons in the ground state of the He atom have their spins parallel to each other.

    (a) True (b)(*) False

31. The noble gas configuration is a particularly stable arrangement of electrons in an atom.

    (a)(*) True (b) False

32. In a metallic bond, the valence electrons are tightly bound to particular atoms and cannot move.

    (a) True (b)(*) False

33. Which of the following two elements is more electronegative, i.e. has a stronger ability to attract electrons?

    (a) Boron (B) (b)(*) Fluorine (F)

34. A single atom can absorb light of any wavelength.

    (a) True (b)(*) False

35. When two waves are in phase, they can reinforce each other by constructive interference.

    (a)(*) True (b) False

36. Sound waves travel faster in interplanetary space than in the Earth's atmosphere.

    (a) True (b)(*) False

37. The amplitude of the standing wave on a string will be maximal when the frequency of the exciting disturbance (e.g., wiggling) is equal to one of the string's characteristic frequencies.

    (a)(*) True (b) False

38. (Photoelectric effect:) The kinetic energy of the electrons emitted from the surface of a photosensitive metal grows with the frequency of the incident light.

    (a)(*) True (b) False

39. The electric charge of an electron is equal and opposite to that of a proton.

    (a)(*) True (b) False

40. When we observe that the spectral lines in light from a distant star are shifted towards shorter wavelengths, we conclude that the star is receding from us.

    (a) True (b)(*) False

41. Elements in the same column (same group) of the Periodic Table have similar properties.

    (a)(*) True (b) False

42. Elements in the periodic table are arranged in order of increasing size of the atom.

    (a) True (b)(*) False

43. Electromagnetic waves need a material medium for their propagation.

    (a) True (b)(*) False

44. Diffraction gratings are used to measure the wavelength of light.

    (a)(*) True (b) False

45. When an atom de-excites, i.e. an electron jumps from a higher energy state to a lower state, light is emitted whose wavelength is determined by the energy difference between the two states.

    (a)(*) True (b) False

46. The set of wavelengths emitted by an atom or molecule is distinctive and can be used to identify it.

    (a)(*) True (b) False

47. Sissy and Sassy are twins. Sissy goes on a trip at close to the speed of light and then returns to Earth.
    1. Since they both experience the same laws of physics, they must have the same age when they meet again on Earth.
    2. Earth is a special frame of reference in which clocks go faster, and so Sissy stays younger than Sassy.
    3. They both have still the same age, but they are much younger than they would be if Sissy had not gone on her trip.
    4. Since neither of them is a preferred observer, they must come to equivalent conclusions about each other: according to Sissy, Sassy is now much older than she is, while according to Sassy, Sissy is now older than Sassy.
    5. (*) Since Sissy spent part of her trip in an accelerated frame of reference, the reference frames of the two are not equivalent; due to time dilation effects, Sissy is now much younger than Sassy who stayed behind.

48. Which of the following compounds is formed by an ionic bond?
    1. 
    2. 
    3. 
    4. (*)
    5. 

49. Which of the following is a molecule formed by a covalent bond?
    1. 
    2. 
    3. (*)
    4. 
    5. 

50. In ``everyday life'' we do not notice evidence for the wave nature of objects that we deal with because
    1. the speed of the particle waves is so large that we cannot see them;
    2. (*) the wavelength associated with everyday objects is so much smaller than their size that the wave effects play no important role;
    3. the wavelength associated with everyday objects is so much larger than their size that the wave effects play no important role;
    4. only small particles in atoms have wave properties;
    5. these wave aspects would only become apparent in UV light which we cannot see.