PHY 1020: Solution to final exam (multiple choice)

PHYSICS 1020

SOLUTION TO FINAL EXAM
22 April 1997
Multiple choice part

If you were on Jupiter, your mass would be much bigger than what it is on earth.

(a) True (b) False
According to Newton's third law, whenever there is a force acting on a body, there is another one acting on it to counteract (balance) it.

(a) True (b) False
What is the bigger energy, a joule or a kWh?
(a) joule (b) kWh
Work and energy have the same units.

(a) True (b) False
Temperature is a measure for the average energy of random motion of the constituents (atoms, molecules) of a substance.

(a) True (b) False
Voltage is related to the difference in electric potential energy between two points.

(a) True (b) False
The kinetic energy of an electron emitted in the photoelectric effect depends on the frequency of the light that causes it to be emitted.

(a) True (b) False
When an atom de-excites, i.e. an electron jumps from a higher energy state to a lower state, light is emitted whose wavelength depends on the speed with which the electron did its jump.

(a) True (b) False
Much of the Earth's internal heat originates from the energy liberated in radioactive decays.

(a) True (b) False
Light moving away from a massive body undergoes ``gravitational redshift'', i.e. its frequency decreases.

(a) True (b) False
Even though the pace of clocks may depend on the relative motion of observer and clock, all observers always agree on whether two events are simultaneous or not.

(a) True (b) False
How is the sun situated in the universe?
1. The sun is at the center of the universe.
2. The sun is just one of a large number of stars, located in the fringes of the Milky Way galaxy, which itself is just one of many galaxies.
3. The sun is just one of the many stars clustered near the center of the universe.
4. Earth is at the center of the universe, and the sun orbits around the earth.
5. The sun is a one-of-a-kind and isolated star that is far outside of all the galaxies in the universe.
A book lying on a table top is given a brief shove; it slides a short distance and then comes to rest. It stopped because
1. being at rest is its natural state.
2. its inertia represents a resistance to motion and makes it stop.
3. gravity pulls it down, so it cannot move horizontally.
4. frictional forces slow it down until it stops.
5. the ether slowed it down.
Which of the following statements is false:
1. A body in uniform motion has no acceleration.
2. In circular motion with constant speed, the acceleration is perpendicular to the velocity.
3. Near the surface of the Earth, free fall is motion with constant acceleration.
4. When a body is in motion, a force must be acting on it.
5. When an object is in free fall, it is being accelerated.
The efficiency of conventional automobiles are at best about 20%. This is mainly due to
1. bad engine design and bad engineering;
2. air resistance and road friction;
3. frictional losses inside the engine and incomplete burning of hydrocarbon fuel;
4. conservation of energy (1st law of thermodynamics);
5. limitation of efficiency due to 2nd law of thermodynamics;
An unmotorized roller coaster car rolls down from the top of a hill into a valley and back up again to the top of another hill (lower than the first), where it comes to a stop. Which are all the energy conversions that have taken place during this trip?
1. gravitational potential (grav.pot.) to kinetic and kinetic to grav.pot.;
2. grav.pot. to kinetic and heat, kinetic to grav.pot., and heat to grav.pot.;
3. chemical to kinetic and kinetic to grav.pot.;
4. grav.pot. to kinetic and heat and kinetic to grav.pot. and heat;
5. chemical to heat and heat to grav.pot.;
Identify the false statement:
1. Work done on a system can increase its internal energy.
2. Heat added to a system can be used to do work and to increase the internal energy of the system.
3. The internal energy of a system depends on its temperature.
4. In a closed, isolated system (i.e no heat exchanged, no work done), the internal energy does not change.
5. In some systems, all the heat added to them is used to do work.
Which of these statements do you agree with?
1. Light is a wave that propagates in a substance called ether which permeates all space.
2. Light is a form of electromagnetic radiation which propagates as a disturbance in an electromagnetic field without material medium as carrier.
3. Light propagates by bouncing from particle to particle (e.g. molecules, water droplets, specks of dust).
4. Light propagates by the motion of tiny charged particles called photons which are accelerated by electric fields.
5. Light needs air for its propagation.
What is the time it takes light to travel from the Moon to Earth?
(The distance is 384000 km).
1. zero time - it is instantaneous;
2. 1/2 second
3. 1.3 seconds
4. 13 seconds
5. 1.3 minutes
Two continuous waves with the same wavelength and amplitude pass through the same position in some medium such that they are ``in phase'', i.e. the crests of one coincide with the crests of the other. The resulting wave has
1. the same wavelength and twice the amplitude;
2. twice the wavelength and the same amplitude as each of the individual waves;
3. zero amplitude;
4. twice the wavelength and twice the amplitude;
5. the same wavelength and the same amplitude;
According to the periodic table of the elements, elements are expected to have similar chemical properties if they
1. are far from each other in the table.
2. are in the same column (``group'') of the periodic table.
3. are in the same row of the periodic table.
4. have about the same weight.
5. have similar names.
An ampere is a unit that is used to express
1. the power it takes to operate an electrical device;
2. the pressure produced by an energy source;
3. how hard it is to push electrons through a wire;
4. the distance the electrons have travelled through a circuit;
5. the amount of electric current flowing in a wire;
A conservation law in physics is a law stating that
1. a certain physical quantity does not change during a physical process, i.e. it is the same before and after.
2. nothing in the Universe is ever lost.
3. natural resources are exhaustible.
4. energy should be conserved, since, once used, it is lost.
5. fossil fuels have been conserved deep in the Earth for a long time.
Which of the following has the longest wavelength:
1. FM radio waves
2. X-rays
3. red light
4. infrared light
5. ultraviolet light
Identify the false statement:
1. Heat will not flow spontaneously from a cold to a hot body.
2. It is not possible to convert heat to work with 100% efficiency.
3. The entropy of a closed system cannot decrease.
4. Every isolated system becomes more disordered with time.
5. Heat can never be moved from a low temperature to a high temperature region (from a cold to a hot body).
Suppose that you are in a spaceship with no means of contact with the outside; you wish to find out if the ship is travelling at a constant speed or is at rest.
1. You can find out by measuring the speed of light inside the ship.
2. You can find out by watching to see if the ship's clocks run slow.
3. There is no way you can find out without contact with the outside world.
4. You can find out by checking if the ship's length is shorter than it should be.
5. You can find out by checking if your mass has gone up due to relativistic mass increase.
Suppose you are in a rocketship in space accelerating at 2g and you drop a ball; how does it move as observed by you?
1. Since there are no forces acting on the ball, it stays put where you let it go, without moving.
2. It moves with constant velocity opposite to the direction of motion of the rocketship.
3. It accelerates with an acceleration of 2g in the direction opposite to the rocketship's acceleration.
4. It accelerates with an acceleration of 2g in the same direction as the rocketship's acceleration.
5. What it does depends on the speed of the rocketship.
According to the ``planetary'' model of the atom, electrons move around a positively charged nucleus, obeying the laws of classical mechanics and electromagnetism. Which of the following statements about this model is false?
1. It states that the nucleus represented most of the atom's mass, but only a small fraction of its volume.
2. It does not account for the discrete lines seen in atomic emission spectra.
3. It predicts that atoms would not be stable.
4. It predicts that most of the space occupied by an atom is empty.
5. It explains most of the regularities and patterns observed in the periodic table of the elements.
Which of the following phenomena demonstrates the existence of light quanta (photons)?
1. refraction
2. diffraction
3. polarization
4. Doppler effect
5. photoelectric effect
A hydrogen atom is in its ground state when its electron
1. is at rest;
2. is in the state with the lowest possible energy;
3. has zero kinetic energy;
4. has escaped from the atom;
5. travels in the largest possible orbit around the proton;
Find the false statement:
1. Heavy nuclei are only stable if they have many more protons than neutrons.
2. Most of the mass of an atom is concentrated in the nucleus.
3. Two atoms with the same number of protons have in general identical chemical properties.
4. Protons are slightly less massive than neutrons.
5. Nuclear bombs are much more powerful than conventional bombs because the nuclear binding energies are about a million times larger than atomic binding energies.
How does the de Broglie wavelength of a proton compare with that of an electron of the same speed? The proton's wavelength is
1. the same as that of the electron;
2. 200 times shorter;
3. 200 times longer;
4. about 1800 times shorter;
5. about 1800 times longer;
Chemical compounds are formed because
1. by forming a bond, atoms can give up, accept or share electrons so that they can achieve a configuration which is energetically more favorable.
2. due to the Pauli principle, the electrons like to stay close together.
3. the strong force between the nuclei of the atoms overcomes the repulsion between the electrons, forcing the atoms to form a bond.
4. when the atoms approach each other, the electrons can form Cooper pairs which are bosons and therefore like to stick together.
5. the magnetic fields generated by the electron clouds of the atoms attract each other.
Identify the correct statement about helium in the earth's atmosphere:
1. There is no helium in the earth's atmosphere - what we need, we have to get from the sun or from Jupiter.
2. Helium is rare - the little there is comes from fusion processes in the upper atmosphere.
3. The helium in the earth's atmosphere comes from radioactive decays in the earth's crust and interior.
4. There is plenty of helium in the earth's atmosphere, but it is difficult to separate it from the other gases.
5. There is plenty of helium in the earth's atmosphere, but it is all in chemical compounds which are difficult to break up because of the helium nucleus' large binding energy.
The half-life of uranium is
1. half of the time after which all the uranium nuclei have decayed;
2. the time after which an individual uranium nucleus splits in half;
3. that time after which about half out of many uranium nuclei have decayed;
4. the time at which the decay of an individual uranium nucleus is half-way completed.
5. half the lifetime of an individual uranium nucleus;
After 12 years, 1/16 of a radioactive isotope remains, while the rest has decayed to something else. The half-life of this isotope is
1. 2 years
2. 3 years
3. 4 years
4. 9 years
5. 12 years
After two light nuclei form a heavier one by fusion, the binding energy per nucleon in the resulting nucleus is in general
1. the same as before;
2. slightly smaller than before;
3. much smaller than before;
4. greater than before;
5. more or less, depending on the particular reaction;
The thermal energy which is used to power the electric generators in a nuclear power plant comes from
1. the radioactive decay of uranium-238;
2. fission processes in which mass energy is converted into kinetic energy;
3. fusion of light water into heavy water;
4. fusion of hydrogen into helium, with conversion of mass energy into kinetic energy;
5. fusion of iron into uranium-235 and plutonium-239;
The purpose of the moderator in a nuclear reactor is to
1. absorb neutrons;
2. slow the neutrons down so that they are less often absorbed by U-238;
3. keep the fuel rods from getting too hot;
4. speed the neutrons up so they will more easily initiate fission;
5. convert U-238 into U-235;
Identify the false statement: According to special relativity,
1. times and distances are always the same for all observers;
2. no massive object can move with a speed greater than the speed of light;
3. the laws of physics are the same in all inertial frames;
4. the speed of light is independent of the relative motion of source and observer;
5. mass is equivalent to energy.
Identify the false statement: According to general relativity,
1. you cannot tell if you are in uniform motion, but it is easy to tell if you are in an accelerated rest frame;
2. every accelerated observer experiences the same laws of nature;
3. the effects produced by the gravitational field and those produced by acceleration are identical and cannot be distinguished from each other;
4. there is no absolute (preferred) accelerated frame;
5. the geometry of space is determined by the distribution of gravitational matter;
Hydrogen must be raised to a very high temperature before it will fuse. This is because
1. the fusion reaction consumes more thermal energy than it produces;
2. fusion needs nuclear energy, which is why thermal energy must be supplied so that it can be converted into nuclear energy;
3. the protons repel each other, and therefore need high kinetic energies to overcome the electric repulsion between them;
4. just like any other combustion process, fusion must be ignited by high temperatures;
5. high temperatures are needed to provide enough kinetic energy to overcome the strong nuclear force between the protons;
Identify the false statement: A clock
1. appears to slow down when it is in motion relative to the observer;
2. goes slower near a massive object than a clock far away from a massive object;
3. appears to go slowest to an observer at rest with respect to the clock;
4. appears to go fastest to an observer at rest with respect to the clock;
5. appears to go slower to an observer who is in motion relative to the clock;
The energy of stars is generated by
1. explosive combustion of hydrogen into water;
2. conversion of gravitational energy into thermal and radiant energy;
3. thermonuclear fusion processes which can be ignited and sustained by the high temperatures and pressures in the stars' cores;
4. radioactive decay of heavy nuclei formed during the Big Bang;
5. nuclear fission of heavy nuclei which where generated by the high pressures during the gravitational contraction of the star when it was formed;
Identify the false statement:
1. Gravity is the weakest of all the interactions, but it has a very long range.
2. The interactions between subatomic particles are mediated by the exchange of particles called ``gauge bosons''.
3. The strong interaction is mediated by the exchange of ``gluons''.
4. Since the gluons have such a small mass, they can move very fast, and this is why the strong force has such a long range.
5. There are four fundamental interactions: gravity, the weak interaction, the electromagnetic and the strong interaction.