Final Test
Spring 1998

PART I: True and False questions. (2 points each, Total of 40 points):
(Note: The answer to Part I is given at the end)

1. When the distance between two stars decreases by half, the force between them increases to four times as much.

2. To say that one wave is out of phase with another is to say that the waves are of different amplitudes.

3. In an elastic collision, colliding objects become distorted, generate heat, and possibly stick together.

4. A standing wave occurs when a wave reflects on itself.

5. If an object falls with constant acceleration, the velocity of the object must be constant also.

6. A Doppler effect occurs when a source of sound does not move.

7. A wave travels an average distance of 1 meter in 1 second with a frequency of 1 hertz. Its amplitude is 1 meter.

8. Neglecting air resistance, objects fall with constant velocity.

9. One object has twice as much mass as another object. The first object also has twice as much inertia.

10. During a single period, the distance traveled by a wave is one wavelength.

11. A sound wave is a transverse wave.

12. Sound travels faster in water than in steel.

13. When the speed of sound near the ground is greater than higher in the air, sound tends to be bent downward.

14. Sound waves can interfere with one another so that no sound results.

15. For FM radio, the letter "F" stands for frequent.

16. A 340-hertz sound wave travels at 340 m/s in air with a wavelength of 10 m.

17. Resonance can be looked at as forced vibration with the matching of wave amplitudes.

18. A main difference between gravitational and electric forces is that electrical forces are weaker.

19. A transistor is similar to a resistor.

20. To say that electric charge is conserved means that no case has ever been found where the total charge on an object has changed.

21. When there is a change in the magnetic field in a closed loop of wire a voltage is induced in the wire

22. A device that transforms electrical energy to mechanical energy is a transformer.

23. The output power of an ideal transformer is equal to the input power.

24. Electric power can be transformed to mechanical power.

25. ac voltage can be transformed via conventional transformers.

26. A generator is a device that produces electric current by rotating a coil of wire within a stationary magnetic field.

27. Magnetic field lines about a current-carrying wire circle the wire in closed loops.

28. Magnetic domains occur in copper.

29. Surrounding every moving electron are a magnetic field and an electric field.

30. The magnetic force between a magnetic field and a moving charge is always perpendicular to both the velocity of the particle and to the magnetic field lines.

31. A magnet cannot attract a piece of iron that is not magnetized.

32. A galvanometer is a sensitive current-indicating instrument.

33. A battery produces dc and the generator at a power station produces ac.

34. The mass of water displaced by a 100-ton floating ship depends on the ship's shape.

35. Energy transfer by convection is primarily restricted to fluids.

36. The first law of thermodynamics is a restatement of the law of energy conservation.

37. Heat a copper wire and its resistance increases.

38. A kitchen could be cooled by leaving the refrigerator door open and closing the kitchen door and windows.

39. The density of gold is greater than the density of aluminum, therefore a kilogram of gold has more volume than a kilogram of aluminum.

40. A 4 ohm resistor is connected in parallel to a 2 ohm resistor. This combination produces a greater resistance than when they are connected in series.



PART II: Multiple Choice Questions. (2 points each, Total of 44 points):

1. Unlike a transverse wave, a longitudinal wave has
a. no amplitude.
b. no frequency.
c. no wavelength.
d. no speed.
e. ...a longitudinal wave has all of these.


2. Which of the following is not a transverse wave?
a. sound.
b. wave in a rope
d. both of these.
e. neither of these.


3. How many vibrations per second are associated with a 101-MHz radio wave?
a. less than 101,000,000.
b. 101,000,000.
c. more than 101,000,000.


4. A 60-vibration-per-second wave travels 30 meters in 1 second. Its frequency is :
a. 30 hertz and it travels at 60 m/s.
b. 60 hertz and it travels at 30 m/s.
c. neither of these.


5. A node is a position of
a. minimum amplitude.
b. maximum amplitude.


6. If you double the frequency of a vibrating object, its period
a. doubles.
b. halves.
c. is quartered.


7. When you are in the way of a fast-moving object and can't get out of its way, you will suffer a smaller force of impact if you decrease its momentum over a:
a. long time.
b. short time.
c. same way either way.


8. A sound source of high frequency emits a high
a- speed.
b- amplitude.
c- pitch.
d- all of these.
e- none of these.


9. Double the frequency of sound and you also double its
a. wavelength.
b. speed.
c. amplitude.
d. all of these.
e. none of these.


10. Compressions and rarefactions are characteristic of
a- longitudinal waves.
b- transverse waves.
c- both of these.
d- neither of these.


11. Sound travels faster in air if the air is
a- warm.
b- cold.
c- neither warm nor cold.


12. The natural frequency of an object depends on its
a. elasticity.
b. size and shape.
c. both of these.
d. neither of these.


13. Some singer is said to have made a crystal glass shatter (break) with his voice. This is a demonstration of
a. an echo.
b. sound refraction.
c. beats.
d. resonance.
e. interference.


14. An explosion occurs 34 km away. Since sound travels at 340 m/s, the time it takes the sound to reach you is
a- 0.1 second.
b- 1 second.
c- 10 seconds.
d- 20 seconds.
e- more than 20 seconds.


15. Which force binds atoms together to form molecules?
a. gravitational.
b. nuclear.
c. electrical.
d. none of these.


16. The unit of electric charge, the coulomb, is the charge on
a. one electron.
b. a specific large number of electrons.


17. The electrical force between charges is strongest when the charges are
a. closer together.
b. far apart.
c. the electric force is constant everywhere.


18. An uncharged small plastic sphere is suspended by a nylon fiber. When a negatively charged rubber rod is brought nearby, without touching it, the small plastic sphere
a. becomes charged by induction.
b. becomes polarized.
c. is repelled by the rod.
d. all of these.
e. none of these.


19. A conductor differs from an insulator in that a conductor
a. has more electrons than protons.
b. has more protons than electrons.
c. has more energy than an insulator.
d. has faster moving molecules.
e. none of these.


20. Two charges separated by one meter exert 1-N forces on each other. If the charges are pulled to 3-m separation distance, the force on each charge will be
a- 0.33 N.
b- 0.11 N.
c- 0 N.
d- 3 N.
e- 9 N.


21. The voltage across the input of a transformer is 110 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer puts out is:
a. 25 V.
b. 55 V.
c. 110 V.
d. 220 V.
e. none of these.


22. A transformer actually transforms
a. voltage.
b. magnetic field lines.
c. generators into motors
d. all of these.


23.____ A device that transforms mechanical energy into electrical energy is a
a. generator.
b. motor.
c. transformer.
d. magnet.
e. none of these.


24. Voltage can be induced in a wire by
a. moving the wire near a magnet.
b. moving a magnet near the wire.
c. changing the current in a nearby wire.
d. all of these.
e. none of these.


25. How does the frequency of induced voltage compare to how frequently a magnet is plunged (dipped) in and out of a coil of wire?
a. greater.
b. smaller.
c. equal.
d. need more information to decide .


26. The force between electrically charged particles depends on
a. the magnitude of charge.
b. the distance of separation.
c. the velocity.
d. all of these.
e. none of these.


27. When a bar magnet is broken in two equal pieces, each piece is
a. as magnetic as the original magnet.
b. actually stronger than the original magnet.
c. half as strong as the original magnet.
d. no longer a magnet.


28. The force of an electron moving in a magnetic field will be the largest when its direction is
a. the same as the magnetic field direction.
b. exactly opposite to the magnetic field direction.
c. perpendicular to the magnetic field direction.
d. none of these.


29. An iron nail is more strongly attracted to the
a. north pole of a magnet.
b. south pole of a magnet.
c. north or south pole - no difference really.


30. Like kinds of magnetic poles repel while unlike kinds of magnetic poles
a. attract.
b. repel also.
c. may attract or repel.


31. The source of all magnetism is
a. tiny pieces of iron.
b. tiny domains of aligned atoms.
c. moving electric charge.
d. none of these.


32. Moving electric charges will interact with
a. an electric field.
b. a magnetic field.
c. both of these.
d. none of these.


33. The rotational motion that electrons exhibit in an atom is:
a. orbital motion.
b. spinning about their axes.
c. both of these.
d. none of these.


34. The principal charge carriers in metal wires are
a. electrons.
b. protons.
c. both of these.
d. none of these.


35. The flow of charge is driven by
a. a pressure difference.
b. a temperature difference.
c. a potential difference.
d. all of these.
e. none of these.


36. The electric power of a lamp that carries 2 A at 120 V is:
a. 1/6 Watts.
b. 2 Watts.
c. 60 Watts.
d. 20 Watts.
e. 240 Watts.


37. The current through a 10-ohm resistor connected to a 120-V power supply is
a. 1 A.
b. 10 A.
c. 12 A.
d. 120 A.


38. Two lamps, one with a thick filament and one with a thin filament of the same material, are connected in parallel to a battery. The current is larger in the lamp with the
a. thick filament.
b. thin filament.
c. current is the same in both.


39. A mosquito flaps its wings 600 vibrations per second, which produces the annoying 600 Hz buzz. The speed of sound is 340 m/s. The wavelength of the mosquito's sound is around:
a. 204 km.
b. 1.76 m.
c. 566.7 mm.
d. none of these.


40. An ice cube measures 10 cm on a side, and floats in water. One cm extends above water level. If you shaved off the 1 cm part, how many of the remaining ice would extend above water level?
a. 0 cm.
b. 1/9 cm.
c. 1 cm.
d. 0.9 cm.



PART III: Fill-In the Blanks (a total of 20 points) :

1. Starting from rest, one car (A) accelerates to a speed of 50 km/h, and another car (B) accelerates to a speed of 60 km / h. Did car (B) car have had the greater acceleration ? ............


2. Can something have energy without having momentum? (yes or no) ...........


3. Can something have momentum without having energy? (yes or no) ...........


4. The mass of a certain neutron star is 3.0x1030 kg and its radius is 8000 m. What is the acceleration of gravity at the surface of this star? (G = 6.67x1011 Nm2 /kg2) ...................


5. How many grams of hydrogen are there in 16 g of methane gas ( CH4 )? ..............


6. A machine gun fires 10 rounds per second. The speed of the bullets is 300 m/s.
a. What is the distance in the air between the flying bullets? ............
b. What happens to the distance between the bullets if the rate of fire is increased? (decreases or increases) ..................


7. Consider a wave generator that produces 10 pulses per second. The speed of the waves is 300 cm / s.
a. What is the wavelength of the waves? ..........
b. What happens to the wavelength if the frequency of pulses is increased? (decreases or increases) ...............


8. If a conductor connected to the terminal of a battery has a potential of 12 volts, then each coulomb of charge on the conductor has a potential energy (PE) of ..................... Joules.


9. A heat pump moves heat from a cooler to a warmer place, and is the heart of a refrigerator or air conditioner. The minimum work input needed to move energy "uphill" from Tcold to Thot t is
Min. work = (Energy moved) * (Thot - Tcold )/ Tcold
Calculate the minimum work needed to move 5 J of energy
a. from inside a room at Tcold = 20 °C to the outdoors at Thot = 33 °C :.....................
b. from inside a lab freezer at Tcold = 173 K to a room at Thot = 293 K :....................


10. Consider a simple transformer that has 100-turn primary coil and a 1000-turn secondary coil. The primary is connected to a 120-V AC source and the secondary is connected to an electrical device with a resistance of 1000 ohms.
a. What will be the voltage output of the secondary? ...........................
b. What current flows in the secondary? ........................
c. Now that you know the voltage and the current, what is the power in the secondary coil? ......................
d. Neglecting small heating losses, and knowing that energy is conserved, what is the power in the primary coil?.........................


11. A flow of 1 ampere is a flow of ......... coulomb per second.



12. For the circuit drawn below, find the current through each resistor, the voltage across each resistor, and the power dissipated as heat in each resistor. (complete the table, total of 3 points).

Resistance (Ohm) Current (A) Voltage (V) Power (W)
5
?
?
?
2
?
?
?