DIAGNOSTIC TEST - SAT Subject Test Physics

SAT Subject Test Physics (2012)

PART II. DIAGNOSTIC TEST

DIAGNOSTIC TEST

Treat this diagnostic test as the actual test, and complete it in one 60-minute sitting. Use the following answer sheet to fill in your multiple-choice answers. Once you have completed the practice test:

1. Check your answers using the Answer Key.

2. Review the Question Answers and Explanations.

3. Complete the Score Sheet to see how well you did.

ANSWER SHEET

Tear out this answer sheet and use it to complete the practice test. Determine the BEST answer for each question. Then fill in the appropriate oval.

DIAGNOSTIC TEST

Part A

Directions: Each set of lettered choices refers to the numbered questions of statements immediately following it. Select the one lettered choice that best answers each question or best fits each statement, and then fill in the corresponding oval on the answer sheet. A choice may be used once, more than once, or not at all in each set.

Questions 1–5 relate to the following physical principles or topics.

(A) pressure

(B) energy

(D) force

(E) acceleration

Select the quantity that each expression defines.

Questions 6–10

(A) quartered

(B) halved

(D) doubled

(E) quadrupled

Two masses, m₁ and m₂, are separated by a distance r, as shown above. Select the effect on the gravitational force of each of the following changes in mass or distance.

6. m₁ is doubled

7. m₁ and m₂ are doubled

8. r is doubled

9. m₁ is doubled, m₂ is halved

10. m₂ is halved

Questions 11–14 relate to the following directions.

(A) out

(B) right

(D) down

(E) zero

Find the direction of the force on a positive charge for each diagram where v is the velocity of the charge, and B is the direction of the magnetic field.

means the vector points inward, into the page.

means the vector points outward, toward the viewer.

Part B

Directions: Each of the questions or incomplete statements below is followed by five suggested answers or completions. Select the one that is best in each case and then fill in the corresponding oval on the answer sheet.

15. A physicist is studying the decay reaction represented above. Particle X is which of the following?

16. The figure above shows two pulses on a string approaching each other. Which of the following diagrams best represents the appearance of the string shortly after the pulses pass point X?

17. How much energy is removed when 10.0 grams of water is cooled from steam at 120°C to liquid at 100°C? (Heat of vaporization for water = 2.26 × 10⁶ joules per kilogram; specific heat of steam = 2.01 × 10³ joules per )

18. Which of these phenomena support(s) the particle model of light?

I. polarization

II. photoelectricity

III. Compton effect

(A) I only

(B) II only

(D) I and II only

(E) II and III only

19. You are in a boat that is traveling due west at 45 kilometers per hour relative to a current that is moving 45 kilometers due south relative to the ground. Your motion relative to the ground is

(A) due west

(B) southwest

(D) northeast

(E) due east

20. In the diagram above, a ray of light strikes a glass prism so that the ray travels through the prism parallel to its base. Which ray correctly shows how the light exits the prism?

Questions 21–22

The diagram above shows an electric circuit containing three resistors. The ammeter, A, reads 5.0 amperes.

21. What is the voltage across R₃?

(A) 5 V

(B) 10 V

(D) 20 V

(E) 50 V

22. What is the current in R₁?

(A) 1.0 A

(B) 2.0 A

(D) 5.0 A

(E) 10 A

23. An object starts from rest and accelerates at 6.0 meters per second squared. How far will it travel during the first 4.0 seconds?

(A) 10 m

(B) 12 m

(D) 36 m

(E) 48 m

24. A heat engine extracts 40 joules of energy from a hot reservoir, does work, then exhausts 30 joules of energy into a cold reservoir. What is the efficiency of the heat engine?

(A) 10%

(B) 25%

(D) 67%

(E) 75%

25. The magnitude of the charge on an ion depends on which of the following?

I. number of electrons

II. number of protons

III. number of neutrons

(A) I only

(B) III only

(D) II and III only

(E) I, II, and III

26. If the mass of a body is doubled while the net force acting on the body remains the same, the acceleration of the body is

(A) halved

(B) doubled

(D) quartered

(E) quadrupled

27. What is the wavelength of the wave?

(A) 0.5 m

(B) 1.0 m

(D) 2.0 m

(E) 3.0 m

28. What is the amplitude of the wave?

(A) 0.5 m

(B) 1.0 m

(D) 3.0 m

(E) It varies between –0.5 m and +0.5 m.

29. If electricity costs $0.10 per kilowatt-hour, how much does it cost for electricity to operate a 1,200-watt television for 2 hours?

(A) $0.024

(B) $0.24

(D) $24.00

(E) $240.00

30. Two freely hanging weights, each having a mass of 20 grams, are connected by a light thread that passes over a fixed pulley. The mass of the pulley and frictional losses are negligible. If a 10-gram weight is now added to one of the weights, its downward acceleration in centimeters per second will be approximately

31. According to the kinetic theory of matter, which of these statements is NOT true about the particles that make up a gas?

(A) The particles of a gas obey the laws of classical mechanics and interact only when they collide.

(B) The speeds of particles in a gas are distributed such that the speeds of most molecules are close to the average.

(D) All particles of a gas have the same speed at the same specified temperature.

(E) The separation between particles is, on average, equal to the diameter of each molecule.

32. Two people are pulling a sled on a sheet of ice. The sled moves in the direction shown by the broken line in the diagram above. If the ice offers no resistance and if Person 1 is pulling with a force of 10 newtons, with what force must Person 2 be pulling?

(A) 0 N

(B) 17 N

(D) 45 N

(E) 60 N

33. In the diagram above, a series of straight wave fronts passes through a small opening in an obstacle. What phenomenon is responsible for this observation?

(A) refraction

(B) photoelectricity

(D) dispersion

(E) polarization

34. The resistance of a conductor decreases when it experiences an increase in

I. length

II. temperature

III. cross-sectional area

(A) I only

(B) II only

(D) II and III only

(E) III only

35. A cylinder with a piston has a cross-sectional area of 0.010 m². How much work can be done by a gas in the cylinder if the gas exerts a constant pressure of 5.0 × 10⁵ Pa on the piston, moving it a distance of 0.020 m?

(A) 0.01 J

(B) 10.0 J

(D) 1000 J

(E) 10,000 J

36. An ice cube is placed in a foam cup filled with warm liquid water. Which principle explains why the ice melts and the system eventually reaches a consistent temperature?

(A) First law of thermodynamics

(B) Second law of thermodynamics

(D) Conservation of momentum

(E) Archimedes’ principle

37. The half-life of iodine–131 is approximately 8 days. About what fraction of a sample of iodine–131 will remain after 32 days?

38. In the circuit shown above, the current I₁ in the 10-ohm resistor is related to the current I₂ in the 30-ohm resister by which of the following equations?

39. An airplane is dropping supplies to firefighters battling a blaze in a forest. In addition to knowing the acceleration due to gravity, what factor(s) must the pilot consider in order to determine where to drop the supplies so that they will land beside the firefighters? (Ignore air resistance.)

I. the speed of the airplane

II. the mass of the supplies

III. the height of the airplane

(A) I only

(B) II only

(D) I and III only

(E) I, II, and III

40. In a darkened room, a beam of monochromatic light is shined on an opaque barrier with a single narrow slit. The light that goes through the slit falls on a screen held parallel to the barrier. Which of the following best describes the intensity of the observed pattern plotted against the distance along the screen?

41. The diagram above relates the temperature of a sample of water to the amount of heat added or removed. Based on the diagram, which of these statements is true?

(A) As pressure rises, a greater amount of latent heat is required for a phase change than at lower pressures.

(B) The latent heat of fusion for water is greater than its latent heat of vaporization.

(D) The amount of latent heat required to change from a solid to a liquid is greater than to change from a liquid to a gas.

(E) A greater amount of latent heat is released when steam changes to liquid water than when the same mass of liquid water changes to ice.

42. A string of length l that is fastened at both ends is plucked in the middle. At the fundamental frequency, the wavelength of the wave in the string is equal to

43. The acceleration of a test vehicle is plotted on the graph above. Based on the graph, what is the acceleration of the vehicle?

(A) 0.2 m/s²

(B) 5 m/s²

(D) 15 m/s²

(E) 36 m/s²

44. A bird drops an acorn from a great height. What is the approximate speed of the acorn, in centimeters per second, after 3 seconds? [Assume the acorn is initially at rest and that the effect of air resistance can be ignored.]

(A) 30 cm/s

(B) 300 cm/s

(D) 3,000 cm/s

(E) 4,000 cm/s

45. A statue is placed in front of a concave lens. What must always be true about the image formed by the lens?

46. What is the current through the 30-ohm resistor in the circuit shown above?

(A) 0.5 A

(B) 1 A

(D) 2.0 A

(E) 3.0 A

47. The graph below plots the velocity, v, of an object over a given period of time, t.

Which graph represents the acceleration, a, of the object during the same period of time?

48. The nucleus of an atom emits a beta particle. As a result, the atomic number

(A) decreases by 2

(B) decreases by 1

(D) increases by 1

(E) increases by 2

49. A meter stick and an observer are located along the x-axis. The meter stick is moving with a velocity of 0.90c along the y-axis. To the observer, the length of the stick will be

(A) zero

(B) less than 1 m

(D) more than 1 m

(E) unpredictable

50. The siren of a moving fire truck emits a sound at a constant frequency. When compared with the sound produced by the siren when it is stationary, how will an observer perceive the sound?

(A) An observer in front of the truck will perceive a sound with a higher frequency.

(B) An observer behind the truck will perceive a sound with a higher frequency.

(D) An observer in the truck will perceive a sound with a lower frequency.

(E) An observer in front of the truck will perceive a sound with a lower frequency.

51. A ball at the end of a string is swinging in a horizontal circle. To calculate the acceleration of the ball, you need to know which factor(s)?

I. speed

II. radius

III. mass

(A) I only

(B) II only

(D) II and III only

(E) I, II, and III

52. The bob of a pendulum completes 21 cycles in 30 seconds. What is its frequency?

(A) 0.7 Hz

(B) 1.4 Hz

(D) 21 Hz

(E) 41 Hz

53. The diagram above represents the motion of a planet around the sun as described by Kepler’s second law. Based on the diagram, which statement about planetary motion is true?

(A) Planets closer to the sun travel at a greater speed than planets farther from the sun.

(B) Planets move fastest in the part of their orbits where they are closest to the sun.

(D) Some planets follow circular paths, whereas others follow elliptical paths.

(E) The period of a planet is determined by its mass, with more massive planets having shorter periods.

54. When the distance between two point charges is doubled, the force between them is

(A) quadrupled

(B) doubled

(D) halved

(E) quartered

55. A transformer changes 12 volts to 24,000 volts. There are 10,000 turns in the secondary coil. How many turns are in the primary? (Assume 100% efficiency.)

(A) 2

(B) 4

(D) 10

(E) 12

Questions 56 and 57 refer to the graph below, which represents the speed of an object moving along a straight line. The time is represented by t.

56. During which interval is the object’s speed increasing?

(A) VW

(B) TU

(D) XY

(E) YZ

57. During which interval is the acceleration constant, but not zero?

(A) ST

(B) TU

(D) XY

(E) YZ

58. A source emits a sound with a frequency of 2.6 × 10⁴ hertz. If the speed of the sound is 3.9 × 10³ meters per second, what is the wavelength of the sound?

59. A negatively charged particle is moving to the right in a plane perpendicular to a uniform magnetic field when it enters the field. If the magnetic field is into the page, which drawing represents the path of the particle once it enters the field?

60. A compact disc is spinning in a CD player. The disc has a small blue marking at one point on its edge. Which of the following is true of the acceleration of the marking while the disc is in motion?

(A) It is zero at all times.

(B) Its magnitude and direction are constant.

(D) It is constant in magnitude, but not direction.

(E) It causes the CD to spin faster.

61. The energy conversion that takes place in a generator is

(A) electrical to mechanical

(B) mechanical to electrical

(D) chemical to electrical

(E) heat to chemical

62. What is the magnitude and direction of the net electric force on particle Q₃ in the figure above due to the other two charges?

(A) The net force is zero.

(B) 0.603 N to the right

(D) 1.35 N to the left

(E) 0.072 N to the right

Questions 63 and 64 relate to the graph below, which shows the net force F in newtons exerted on a 2-kilogram block as a function of time t in seconds. Assume the block is at rest at and that F acts in a fixed direction.

63. Which statement is true about the motion of the block during the time interval from 2 to 5 seconds?

(A) The block is not moving.

(B) The acceleration is constant.

(D) The speed of the block is constant.

(E) The force on the block is decreasing.

64. The acceleration of the block at seconds is

(B) 2 m/s²

(D) 6 m/s²

(E) 18 m/s²

65. An object is placed 30 centimeters in front of a converging lens of focal length 10 centimeters. If the image is 15 centimeters from the lens, what is the magnification?

(A) 0.5

(B) 1.0

(D) 2.0

(E) 5.0

66. A steel girder is 10 meters long at 20°C. By what length will the girder expand if the temperature rises to 50°C? (The coefficient of linear expansion for steel is 12 × 10^–6/°C.)

67. In 1923, Louis de Broglie made a major contribution to the study of physics. De Broglie proposed the idea that

(A) the basic laws of physics are the same in all inertial reference frames.

(B) light consists of fluctuating electric and magnetic fields.

(D) light can be described in terms of discrete units called photons.

(E) material particles have wavelengths related to their momentum.

68. A football player kicks a football from ground level at an angle of 45° above the horizontal. The player then kicks the ball again with the same speed, but at an angle of 30° above the horizontal. Which diagram correctly shows the trajectories of the balls?

69. Which of these measurements has three significant digits?

I. 39.2 g

II. 0.05103 cm

III. 1860 L

(A) I only

(B) II only

(D) II and III only

(E) I and III only

Questions 70 and 71

Some of the energy levels of hydrogen are shown in the diagram above.

70. Which expression can be used to find the frequency, in hertz, of the light emitted during the transition from

71. Which of these transitions will result in the emission of a photon with the least amount of energy?

72. A flower is placed into a clear vase of water. To an observer on the side of the vase, the stem appears to be bent where it enters the water. What phenomenon causes the stem to appear bent?

(A) polarization

(B) photoelectricity

(D) reflection

(E) refraction

73. Two forces are being exerted on an object in the horizontal direction. If these are the only forces acting on the object, which pair of forces can result in a net force of 18 newtons?

(A) 18 N, 18 N

(B) 12 N, 8 N

(D) 22 N, 18 N

(E) 15 N, 13 N

74. A bob suspended by a string of length, l, forms a simple pendulum as it swings back and forth. If the angle displacement is small, upon what does the period of the pendulum depend?

I. mass of the bob

II. length of the string

III. amplitude

(A) I only

(B) II only

(D) I and III only

(E) I and II only

75. In 1911, Ernest Rutherford and his associates conducted an experiment in which they bombarded a thin, gold foil with fast-moving alpha particles. What surprising observation did they make during this experiment?

(A) Most particles experienced wide-angle deflections.

(B) A small number of particles were redirected toward their source.

(D) Some particles were absorbed by the foil and disappeared.

(E) Many particles experienced a change in charge as they hit the foil.

STOP

IF YOU FINISH BEFORE TIME IS CALLED, YOU MAY CHECK YOUR WORK ON THIS TEST ONLY.
DO NOT TURN TO ANY OTHER TEST IN THIS BOOK.

ANSWER KEY

1. C

2. E

3. B

4. A

5. D

6. D

7. E

8. A

9. C

10. B

11. B

12. A

13. E

14. C

15. D

16. E

17. B

18. E

19. B

20. D

21. E

22. C

23. E

24. B

25. C

26. A

27. E

28. A

29. B

30. C

31. E

32. B

33. C

34. E

35. C

36. B

37. D

38. D

39. D

40. B

41. E

42. D

43. B

44. D

45. A

46. C

47. B

48. D

49. C

50. A

51. C

52. A

53. B

54. E

55. C

56. C

57. E

58. C

59. A

60. D

61. B

62. C

63. B

64. C

65. A

66. C

67. E

68. D

69. E

70. B

71. A

72. E

73. C

74. B

75. B

QUESTION ANSWERS AND EXPLANATIONS

1. C This formula can be rewritten as

which is the change in kinetic energy. The net work done on an object is equal to its change in kinetic energy.

2. E This formula can be used to determine the acceleration of an object in circular motion.

3. B This formula describes the potential energy of charge q₂ in the presence of charge q₁ a distance r away.

4. A This rearrangement of the ideal gas law solves for pressure (P), which is equal to the product of the number of moles (n), the constant of proportionality (R), and temperature (T) divided by volume (V).

5. D This formula can be rewritten as either

where p represents momentum and t represents time, or

where m represents mass, a represents acceleration, and t represents time. According to Newton’s second law of motion, both of these are equal to force.

6. D The gravitational force between the masses is determined by

The force is directly proportional to mass, so if one mass is doubled, the force is also doubled.

7. E The gravitational force between the masses is determined by

The force is directly proportional to mass, so if both masses are doubled, the force is multiplied by 4.

8. A The gravitational force between the masses is determined by

The force is inversely proportional to the square of the distance between the mass, so if the distance is doubled, the force is divided by 1/4.

9. C The gravitational force between the masses is determined by

The force is directly proportional to mass, so if one mass is doubled but the other is halved, there is no overall change in the force.

10. B The gravitational force between the masses is determined by

The force is directly proportional to mass, so if one mass is divided by two, the force is also divided by 2.

11. B The direction of the force is perpendicular to the magnetic field and to the velocity of the particle. Using the right-hand rule, orient your hand so that your outstretched fingers point in the direction of motion of the particle. When you bend your fingers, they should point downward in the direction of the magnetic field. Your thumb will point to the right, in the direction of the force.

12. A The direction of the force is perpendicular to the magnetic field and to the velocity of the particle. Using the right-hand rule, orient your hand so that your palm is flat with your fingers pointing toward the right. Your thumb will then point out of the page, in the direction of the force.

13. E The force is zero if the particle moves parallel to the field lines.

14. C The direction of the force is perpendicular to the magnetic field and to the velocity of the particle. Using the right-hand rule, orient your hand so that your palm faces you and your fingers point toward the left. Your thumb will point upward, in the direction of the force.

15. D Consider X as . Particle X must balance the equation. Solve , so . Solve so . Thus, X must be .

16. E Two pulses traveling in opposite directions on the same string pass each other without being changed.

17. B First, find the heat loss to cool the steam from 120°C to 100°C: Steam cooling from 120°C to .

Steam condensing to water: .

The total energy loss is .

18. E Photoelectricity is produced when electrons are emitted from a surface as a result of photons of incident light. According to the Compton effect, scattered light has a slightly shorter wavelength than incident light because of a loss of energy that occurs as photons collide with electrons in the material. Polarization occurs when light waves in specific directions are blocked from passing through a material.

19. B Both vectors have the same magnitude. The westward vector combines with the southward vector to form a vector in the southwest direction.

20. D As the light exists the prism, it is bent at the same angle at which it entered the prism.

21. E The voltage is equal to the current measured at the ammeter multiplied by the resistance of R₃.

22. C The 5.0 A enters the junction leading to R₁ and R₂. Because , the current divides evenly.

23. E The distance where a is the accelerationand t is the time. For this object, .

24. B The efficiency is found by .

25. C Electrons are negatively charged subatomic particles. Protons are positively charged subatomic particles. Neutrons are neutral subatomic particles. In an atom, the electrons and protons are balanced. An ion is an atom that has gained or lost electrons. The difference between the number of electrons and protons determines the charge of the ion.

26. A According the Newton’s second law of motion, the net force acting on an object is proportional to the product of mass and acceleration. If the mass is doubled, the force must, therefore, be halved.

27. E The wavelength is the distance between two consecutive points on the wave. For example, the first cycle of the wave begins at 0 meter and is complete at 3.0 meters.

28. A The amplitude is the maximum disturbance from the resting position. It is the distance from rest to crest or to trough, which is 0.5 meter.

29. B The energy provided is found by . In this case, kwhr. The cost is found by multiplying the number of kilowatt hours by the price per kilowatt-hour. The total cost, C = (2.4 kwhr)($0.10/kwhr) = $0.24.

30. C The solution requires

Therefore,

31. E On average, the molecules of a gas are far apart from one another. Their average separation is much greater than the diameter of each molecule.

32. B If the sled is moving in a horizontal direction, the vertical components of the forces must cancel out. The vertical component of Person 1’s force is F sin 60°, . Therefore, the vertical component of Person 2’s force must also be 8.66 N. This information can be used to find the net force of Person 2. so , .

33. C As the wave goes through the slit, it spreads out behind the obstacle. The bending of a wave around an obstacle is diffraction.

34. E Resistance generally increases with temperature and length. It decreases as the cross-sectional area increases.

35. C First find the change in the volume of the cylinder: . Then use the change in volume to calculate the work done: .

36. B Entropy is a measure of a system’s disorder. As the ice cube melts, the entropy of the molecules increases. According to the second law of thermodynamics, the entropy of the universe increases through all natural processes.

37. D Approximately four half-lives occur in 32 days.

38. D The same current passes through each resistor in a series circuit. If this were not true, charge would have to accumulate somewhere in the circuit.

39. D The acceleration due to gravity is independent of mass and therefore depends on the speed and height of the airplane only.

40. B The diffraction pattern would be a series of rectangular, parallel bands of light. The central band would be brightest, and the bands to the side decrease in brightness in either direction.

41. E The horizontal portions of the diagram indicate that heat is being added to or removed from the sample without resulting in a temperature change. These changes in heat result in phase changes. The length of the line is related to the amount of heat loss required for the change. The length of the steam to liquid water line is considerably longer than the length of the liquid water to ice line.

42. D The string naturally vibrates at certain frequencies. The lowest of these natural frequencies is the fundamental frequency. At this frequency, the wavelength in the string is twice the length of the string.

43. B Reading the graph shows that the vehicle accelerated at a constant rate from 5 m/s to 35 m/s in 6 seconds. Acceleration is equal to the change in velocity divided by the elapsed time,

44. D The acceleration due to gravity is 980 cm/s². The speed is found by .

45. A A concave lens always forms a virtual image that is smaller than the object and is oriented in the same direction as the object.

46. C The voltage of 60 V is applied across both branches of the parallel circuit. The total resistance across the branch with the 30-ohm resistor is 40 ohms. For that branch, .

47. B The straight line with a positive slope indicates that the velocity is increasing at a constant rate. This means that the object is moving with constant acceleration as indicated by a horizontal line for it acceleration graph.

48. D The release of a beta particle occurs when a neutron breaks into an electron and a proton. The electron is emitted, and the proton remains in the nucleus. The atomic number depends on the number of protons in the nucleus, so the atomic number increases by 1.

49. C If the meter stick is along the x-axis, and the motion is in the y-direction, there will not be any observed change in length.

50. A As the truck moves forward, the sound waves bunch together. An observer hears a sound with a higher frequency than the sound produced by the siren.

51. C The acceleration of the ball is determined by dividing the square of the velocity by the radius of the circle. It is independent of the mass of the ball.

52. A Frequency is the number of vibrations per second. Therefore, .

53. B According to Kepler’s second law, planets sweep out equal areas in equal periods of time. Therefore, planets must move faster when they are closer to the sun than when they are farther away.

54. E The force between two point charges is inversely proportional to the square of the distance between them. If the distance is doubled, the force is divided by .

55. C The number of turns is related to the voltage by

56. C Speed is increasing when the graph has a positive slope.

57. E The acceleration is constant but not zero when the graph shows a straight, but not horizontal, line.

58. C Wavelength is equal to speed divided by frequency. For this wave, wavelength equals 3.9 × 10³ meters per second divided by 2.6 × 10⁴ hertz.

59. A The negative charge would move in a clockwise circle. A positive charge would move in a counterclockwise direction.

60. D Once the CD is in motion, its speed does not change. Because it is in circular motion, the direction is constantly changing. Therefore, a point on the edge of the disc accelerates at a constant speed, but changing direction.

61. B A generator is the opposite of a motor in that it uses the mechanical energy of a moving armature to produce an electric current.

62. C Calculate the net electric force on the particle due to the other two charges.

The negative sign indicates an attractive force, in this case toward Q₂.

63. B The force and mass are constant during this interval. Therefore, the acceleration is also constant. The block continues to speed up, but at a constant rate.

64. C At seconds, the force is 6 N. According to Newton’s second law of motion, . So , which means that .

65. A The magnification equals the distance from the image to the lens, 15 centimeters, divided by the distance from the object to the lens, 30 centimeters.

66. C The expansion L can be found by , where α, is the coefficient of linear expansion, L^o is the original length, and T is the change in temperature. In this situation, .

67. E In addition to his many other contributions to science, De Broglie is credited with recognizing that matter can be described by wave properties just as light can be described by properties of matter.

68. D The maximum range occurs at an angle of 45° for a given velocity. Therefore, the ball kicked at this angle will travel farther than the ball kicked at a smaller angle.

69. E All nonzero digits are significant. Zeros appearing between nonzero digits are significant. Zeros at the end of a number with no decimal point written are not significant.

70. B The frequency is proportional to its energy, . The energy is determined by subtracting the energy of the first state from the energy of the second state: Each electron-volt of energy is equal to 1.6 × 10^–19 J. Multiplying this by 10.2 eV yields 1.63 × 10^–18 J. And .

71. A Compare the energy difference for each transition by subtracting the two values. For . . . . .

72. E Refraction is the bending of light when it moves from one medium to another at an angle. This bending will cause the stem to appear bent.

73. C If these forces act in opposite directions, the net force is the difference between them .

74. B For small-angle displacements, the period of a simple pendulum depends only on the length of the pendulum.

75. B Rutherford expected the particles to go directly through the foil. However, about 1 in every 8,000 alpha particles was reflected back to the source. This observation led Rutherford to conclude that an atom contains a small, central core with a positive charge.