Final Test
Fall 1997
PART I: True or False questions. (1 points each, Total of 40 points):


1. Voltage can be induced in a loop of wire by changing a current in a nearby loop.

2. A dam is thicker at the bottom than at the top because water is denser at deeper levels.

3. The force of gravity changes the speed of a satellite in elliptical orbit.

4. A black hole is an empty region of space with huge gravitational field.

5. The lowest possible temperature is the absolute zero.

6. Like magnetic poles attract and opposite poles repel.

7. Water will float on mercury because water is denser than mercury.

8. In a series circuit, the voltage drop across each device is proportional to its resistance.

9. A substance that heats up relatively quickly has a low specific heat.

10. The kinetic energy of a satellite moving in a circular orbit is always constant .

11. If you place an iron core inside a coil with circulating current, the magnetic field is higher because of the alignment of magnetic domains in the direction of the magnetic field of the coil.

12. An iron rod becomes magnetic when its atoms are aligned having plus charges on one side and negative charges on the other.

13. According to Newton, tripling the distance between two interacting objects increases by 9 times the gravitational force between them.

14. Acceleration due to gravity on the moon is similar to that on the earth .

15. Lifting a 10 kg bag vertically 5 meters requires the same amount of work as lifting a 50 kg bag vertically 1 meter.

16. Momentum is a vector quantity.

17. A car travels in a circle with constant speed. The car experiences a centripetal force directed towards the center of the curve.

18. A copper coil has the properties of a bar magnet even when it is not carrying any current.

19. Compared to the resistance of two resistors connected in series, the same resistors connected in parallel have less resistance .

20. The magnetic north pole of the earth is nearest Australia (in the southern hemisphere)

21. The phenomenon of beats results from sound interference.

22. Doppler effect occurs only when a source of sound moves towards you.

23. The natural frequency of an object depends on its elasticity and shape.

24. Melting snow cools the surrounding air.

25. In a parallel circuit, as the number of parallel branches is increased, the overall resistance of the circuit is increased.

26. The force between a positive charge and a negative charge increases as they approach each other.

27. Sound travels faster in solids than in liquids.

28. A conductor has more electrons than protons.

29. At higher altitudes above the sea level, the boiling temperature of water is less than 100 °C.

30. The temperature of a gas always increases when it is subject to an adiabatic process.

31. A good heat conductor is also a good insulator.

32. Magnetism and electricity are independent of each other

33. When a rock is fired upwards gets to the exact top of its path, its velocity is zero but its acceleration is different from zero.

34. The headlights, radio, and defroster fan in an automobile are connected in series.

35. If a steady magnetic field exerts a force on a moving charge, that force is directed at right angles to the direction of the motion.

36. The source of all magnetism is tiny domains of aligned atoms.

37. Silver warms up faster than iron when heat is applied therefore silver cools faster when heat is removed

38. If an object's mass is decreasing while a constant force is applied to the object, the acceleration increases.

39. A possible cause for the existence of the earth's magnetic field is convection currents in the liquid part of the earth's core.

40. A capacitor is used to store charge and energy.

Answer ( Part I ) True Answers: 1, 3, 5, 8, 9, 10, 11, 15, 16, 17, 19, 20, 21, 23, 24, 26, 27, 29, 33, 35, 37, 38, 39 and 40False Answers: remaining



PART II: Multiple Choice Questions. (1 points each, Total of 40 points):

1. 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.
e- none of these.
Answer c

2. An ampere is a unit of electrical
a- pressure.
b- current.
c- resistance.
d- all of these.
e- none of these.
Answer b

3. Heat a copper wire and its electric resistance
a- decreases.
b-remains unchanged.
c- increases.
Answer c

4. Drop a rock from a 10 m height and it accelerates at 10 m/s²and strikes the ground 1s later. Drop the same rock from a height of 5 m and its acceleration of fall is
a- about half
b- the same
c- more
Answer b

5. In an ac circuit, the electric field
a- increases via the inverse square law.
b- changes magnitude and direction with time.
c- is everywhere the same.
d- is non existent.
e- none of these.
Answer b

6. According to Kepler's third, the period T of the planets and their average distances R from the sun are related to each other as follows:
a- T³ is proportional to R².
b- T³is inversely proportional to R².
c- T²is proportional to R³.
d- T²is inversely proportional to R³.
Answer c

7. A 10 N falling object encounters 10 N of air resistance. The net force on the object is
a. 0 N
b. 4 N
c. 6 N
d. 10 N
Answer a

8. When a 10 V battery is connected to a resistor, the current in the resistor is 2 A. What is the resistor's value?
a- 2 ohms.
b- 5 ohms.
c- 10 ohms.
d- 20 ohms.
e- more than 20 ohms.
Answer b

9. Alternating current is normally produced by a
a- battery.
b- generator.
c- both of these.
d- none of these.
Answer b

10. Consider a piece of metal that has a temperature 10 K. If it is heated until it has twice the internal energy, its temperature will be
a. 20 K.
b. 273 K.
c. 293 K.
d. 566 K.
Answer a

11. The resistance of one's body is increased by
a- moisture (water on skin).
b- salt due to perspiration.
c- both (a) and (b)
d- none of the above
Answer c

12. During an electric shock, what is harmful for the human body?
a- high current.
b- high voltage.
c- high resistance of the body.
d- all of these.
e- none of these.
Answer a

13. A man leans over the edge of a cliff and throws a rock upward at 10 m/s. How far below the level from which it was thrown is the rock 2 seconds later?
a. 5 m
b. 10 m
c. 0 m
d. 20 m
Answer c

14. Magnetic field lines about a current-carrying wire
a- extend radially from the wire.
b- circle the wire in closed loops.
c- both of these.
d- neither of these.
Answer b

15. Which pole of a compass needle points to a south pole of a magnet?
a- North pole.
b-south pole.
c- both (a) and (b).
Answer a

16. A moving proton
a- is actually an electric current.
b- produces an electric field.
c- produces a magnetic field.
d- all of the above.
Answer d

17. The force on an electron moving in a 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.
Answer c

18. Particle A attracts particle B which has half the charge of particle A. Compared to the force on particle B, the force on particle A is
a- four times less.
b- two times as much.
c- the same.
d- four times as much.
Answer c

19. Electrons are made to flow in a wire when there is
a- an imbalance of charges in the wire.
b- more potential energy at one end of the wire than the other.
c- a potential difference across its ends.
Answer c

20. If a projectile is fired straight up at a speed of 10 m/s, the total time to return to its starting position is about
a- 1 second
b- 2 seconds
c- 10 seconds
d- not enough information to estimate
Answer b

21. The ideal efficiency (Carnot) is given by e = 1- T_cold/T _hot
a- decreasing T_cold will contribute to a higher increase in efficiency than increasing T_hot by the same amount.
b- decreasing T_cold will contribute to a smaller increase in efficiency than increasing T_hot by the same amount.
c- decreasing T_coldwill contribute to the same increase in efficiency as increasing T_hot by the same amount.
d- none of the above.
Answer a

22. Stretch a copper wire so that it is thinner and the resistance between its ends
a- decreases.
b-remains unchanged.
c- increases.
Answer c

23. Two projectiles are fired from ground level at equal speeds but different angles. One is fired at an angle 30 degrees and the other at 60 degrees. The projectile to hit the ground first will be the one fired at (neglect air resistance)
a- 30 degrees.
b- 60 degrees.
c- both hit at the same time.
Answer a

24. Your weight is
a- actually your mass.
b- the gravitational attraction between you and the earth.
c- a property of mechanical equilibrium.
d- all of these.
e- none of these.
Answer b

25. Which of the following are electrically neutral?
a. proton.
b. neutron.
c. electron.
d. all of these.
e. none of these
Answer b

26. Temperature is
a. a measure of heat
b. a relative measure of hotness and coldness
c. both (a) and (b)
Answer b

27. What is the mass of water displaced by a 55_ton floating ship?
a. less than 50 tons.
b. 50 tons.
c. more than 50 tones.
d. 50 m³
e. depends on the ship's shape.
Answer c

28. The specific heat of substance A is ten times less than that of substance B. If equal amounts of heat are added to equal masses of A and B, the temperature increase of substance A is
a. the same as that of B
b. ten times greater than that of B
c. ten times less than that of B
d. none of the preceding.
Answer b

29. Consider two planets in space that gravitationally attract each other. If the masses of both planets are halved, and the distance between them is also halved, then the force between them is
a. one quarter.
b. half as much.
c. twice as much.
d. four time as much.
e. none of these.
Answer e

30. If the volume and the mass of an object were to double, its density would
a. halve.
b. double.
c. stays the same.
Answer c

31. Heat energy is measured in units of
a. joules.
b. calories.
c. Calories.
d. all of these.
Answer d

32. The ideal efficiency for a heat engine operating between the temperatures of 400 K and 300 K is
a. 20%.
b. 25%.
c. 40%.
d. 88%.
e. none of these.
Answer b

33. The electric power of a lamp that carries 2 A at 120 V is
a- 60 W.
b- 240 W.
c- 480 W.
d- none of these.
Answer b

34. The energy of sound in air eventually becomes
a. heat in air.
b. weaker and weaker until it disappears.
c. canceled by destructive interference.
d. none of these.
Answer a

35. We feel warmed by condensation because water molecules in the air that strike our bodies
a. form an insulating layer on our bodies.
b. gain kinetic energy as they change state.
c. transfer some of their kinetic energy to us.
d. all of these.
Answer c

36. When a volume of air is expanded adiabatically, the temperature will
a. increase.
b. decrease.
c. remain unchanged.
Answer b

37. An object travels 8 meters in the first second of travel, 8 meters again during the 2nd second of travel, and 8 meters again during the third second. Its acceleration in meters per second per second is
a. 0
b. 5
c. 8
d. 10
Answer a

38. 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.
d- more information is needed.
Answer c

39. A bug sits on a record player whose angular speed is constant. If it moves to a point twice as far from the center, then its angular speed
a. doubles
b. halves
c. remains the same
Answer c

40. A 10 Ohm resistor has a 5 A current in it. What is the voltage across the resistor.
a-5 V.
b-10 V.
c- 15 V.
d- 20 V.
e- more than 20 V.
Answer e



PART III: Fill-In the Blanks (1 point for each blank, a total of 20 points) :

1. A simple instrument designed to detect electric current is the .....................; when it is calibrated to measure current, it is an .....................;when it is calibrated to measure voltage, it is a .....................
Answer Galvanometer Ammeter Voltmeter

2. A 100 ton ship is floating on water (density of water is 1000 kg/m³).
a. What is the mass of water displaced by the ship? .....................
b. What is the weight of the ship? .....................
c. What is the buoyant force on the ship? .....................
d. What is the net force on the ship? .....................
Answer a) 100 ton b) 10^6 N c) 10^6 N d) 0 N

3. Consider the following parallel circuit:

a. The voltage across each resistor is: .....................V.
b. The current in each branch is:
1 ohms resistor .....................A
2 ohms resistor .....................A
3 ohms resistor .....................A
c. The current through the battery equals the sum of the currents which equals .....................A
d. The equivalent resistance of the circuit is .....................Ohm
e. If the three resistors were connected in series the equivalent resistance of the circuit would be .....................Ohm
Answer a) 6 V b) 6A; 3A; 2A c) 11 A d) 6/11 Ohm = 0.54 Ohm e) 6 Ohm

4. A 60 W night light is plugged into a 220 V circuit and operates continuously for 10 hours. the current it draws is .....................
the resistance of its filament is .....................
the energy consumed in 10 hours is .....................
Answer a) 60/220 = 0.27 A b) 220/(60/220) = 814 Ohm c) 60W*10h =600 Wh

5.

Find the current through each resistor, the voltage across each resistor, and the power dissipated as heat in each resistor. (complete the table, 3 marks)

Resistance (Ohm)	Current (A)	Voltage (V)	Power (W)
2	?	?	?
6	?	?	?

Answer The 2 Ohm resistance: I =2A, V=4V and P = 8W The 6 Ohm resistance: I =2A, V=12V and P = 24W