Physics Exam 1 Concept Questions

Michael Faraday

"map" electric field lines

Two observation points are located at distances r1 and r2 from a source of sound. The sound spreads out uniformly from the source, and there are no reflecting surfaces in the environment. The sound intensity level at distance r2 is 6 dB less than the level at distance r1. (a) What is the ratio I2/I1 of the sound intensities at the two distances? (b) What is the ratio of r2/r1 of the distances?

(a) 1/4 (b) 2

For two wave sources vibrating out of phase, a difference in path lengths that is (1) ____ of wavelengths leads to constructive interference; a difference in path lengths that is (2) ____ of wavelengths leads to destructive interference.

(1) half integer (2) zero or an integer

For two wave sources vibrating in phase, a difference in path lengths that is (1)____ of wavelengths leads to constructive interference; a difference in path lengths that is a (2)____ of wavelengths leads to destructive interference.

(1) zero or integer (1,2,3...) (2) half interger (1/2, 3/2...)

At a swimming pool, a music fan up on a diving platform is listening to a radio. As the radio is playing a tone that has a constant frequency Fs, it is accidentally knocked off the platform. Describe the Doppler effect heard by (a) the person on the platform and (b) a person down below in the water. In each case, state whether the observed frequency Fo is greater or smaller than Fs and describe how Fc changes (if it changes) as the radio falls.

(a) Fo is smaller than Fs and Fo decreases during the fall. (b) Fo is greater than Fs, and Fo increases during the fall.

A cylindrical bottle, partially filled with water, is open at the top. When you blow across the top of the bottle a standing wave is set up inside it. Is there a node or an antinode (a) at the top of the bottle and (b) at the surface of the water (C) If the standing wave is vibrating at its fundamental frequency, what is the distance between the top of the bottle and the surface of the water? Express your answer in terms of the wavelength of the standing wave. (d) If you take a sip from the bottle, is the fundamental frequency of the standing wave raised, lowered, or does it remain the same?

(a) antinode (b) node (C) 1/4 wavelength (d) lowered

When a truck is stationary, its horn produces a frequency of 500 Hz. You are driving your car, and this truck is following behind. You hear its horn at a frequency of 520 Hz. (a) Refer to Equation 16.15 and decide which algebraic sign should be used in the numerator and which in the denominator. (b) Which driver, if either, is driving faster?

(a) minus sign in both places (b) the truck driver

Refer to Example 1 in Section 16.2. Which type of radio wave, AM or FM, diffracts more readily around a given obstacle? (a)AM, because it has a greater wavelength (b)FM, because it has a greater wavelength (c)AM, because it has a greater frequency (d)FM, because it has a greater frequency

(a)AM, because it has a greater wavelength

As indicated in Figure 16.9, the speed of a transverse wave on a string is Vwave, and the speed at which a string particle moves is Vparticle. Which of the following statements is correct? (a) The speeds Vwave and Vparticle are identical. (b) The speeds Vwave and Vparticle are different.

(b) The speeds Vwave and Vparticle are different.

Suppose that the person singing in the shower in Figure 16.24 produces a sound power . Sound reflects from the surrounding shower stall. At a distance in front of the person, does the expression I= P/(4pir^2) (Equation 16.9) (a) overestimate, (b) underestimate, or (c) give the correct total sound intensity?

(b) underestimate

A rod made from insulating material carries a net charge (which may be positive or negative), whereas a copper sphere is electrically neutral. The rod is held close to the sphere but does not touch it. Which one of the following statements concerning the forces that the rod and sphere exert on each other is true? (a)The forces are always attractive. (b)The forces are always repulsive. (c)The forces are attractive when the rod is negative and repulsive when it is positive. (d)The forces are repulsive when the rod is negative and attractive when it is positive. (e)There are no forces.

(a)The forces are always attractive.

A wind instrument is brought into a warm house from the cold outdoors. What happens to the natural frequencies of the instrument? Neglect any change in the length of the instrument. (a)They increase. (b)They decrease. (c)They remain the same.

(a)They increase.

A positive point charge is located to the left of a negative point charge. When both charges have the same magnitude, there is no place on the line passing through both charges where the net electric field due to the two charges is zero. Suppose, however, that the negative charge has a greater magnitude than the positive charge. On which part of the line, if any, is a place of zero net electric field now located? (a)To the left of the positive charge (b)Between the two charges (c)To the right of the negative charge (d)There is no zero place.

(a)To the left of the positive charge

Starting at the overlap point in Figure 17.3, you walk along a path that is parallel to the line between the speakers. As you walk, the loudness of the sound (a)changes from loud to faint to loud (b)changes from faint to loud to faint (c)does not change.

(a)changes from loud to faint to loud

A source of sound produces the same frequency under water as it does in air. This source has the same velocity in air as it does under water. Consider the ratio Fo/Fs of the observed frequency Fo to the source frequency Fs. Is this ratio greater in air or under water when the source (a) approaches and (b) moves away from the observer?

(a)greater in air (b)greater under water

Two metal spheres are identical. They are electrically neutral and are touching. An electrically charged ebonite rod is then brought near the spheres without touching them, as the drawing shows. After a while, with the rod held in place, the spheres are separated, and the rod is then removed. The following statements refer to the masses mA and mB of the spheres after they are separated and the rod is removed. Which one or more of the statements is true? (a) mA= mB (b) mA> mB if the rod is positive (c) mA< mB if the rod is positive (d) mA> mB if the rod is negative (e) mA< mB if the rod is negative

(b) mA> mB if the rod is positive (e) mA< mB if the rod is negative

Identical point charges are fixed to diagonally opposite corners of a square. Where does a third point charge experience the greater force? (a)At the center of the square (b)At one of the empty corners (c)The question is unanswerable because the polarities of the charges are not given.

(b)At one of the empty corners

The tension in a guitar string is doubled. By what factor does the frequency of the vibrating string change? (a)It increases by a factor of 2. (b)It increases by a factor of sqr 2. (c)It decreases by a factor of 2. (d)It decreases by a factor of sqr 2.

(b)It increases by a factor of sqr 2.

A tuning fork has a frequency of 440 Hz. The string of a violin and this tuning fork, when sounded together, produce a beat frequency of 1 Hz. From these two pieces of information alone, is it possible to determine the exact frequency of the violin string? (a)Yes; the frequency of the violin string is 441 Hz. (b)No, because the frequency of the violin string could be either 439 or 441 Hz. (c)Yes; the frequency of the violin string is 439 Hz.

(b)No, because the frequency of the violin string could be either 439 or 441 Hz.

There is an electric field at point P. A very small positive charge is placed at this point and experiences a force. Then the positive charge is replaced by a very small negative charge that has a magnitude different from that of the positive charge. Which one of the following statements is true concerning the forces that these charges experience at P? (a)They are identical. (b)They have the same magnitude but different directions. (c)They have different magnitudes but the same direction. (d)They have different magnitudes and different directions.

(b)They have the same magnitude but different directions.

Suppose that you are sitting at the overlap point between the two speakers in Figure 17.4. Because of destructive interference, you hear no sound, even though both speakers are emitting identical sound waves. One of the speakers is suddenly shut off. Will you now hear a sound? (a)No. (b)Yes. (c)Yes, but only if you move a distance of one wavelength closer to the speaker that is still producing sound.

(b)Yes.

A rope is hanging vertically straight down. The top end is being vibrated back and forth, and a standing wave with many loops develops on the rope, analogous (but not identical) to a standing wave on a horizontal rope. The rope has mass. The separation between successive nodes is (a)everywhere the same along the rope (b)greater near the top of the rope than near the bottom (c)greater near the bottom of the rope than near the top.

(b)greater near the top of the rope than near the bottom

Tuning fork A (frequency unknown) and tuning fork B (frequency= 348 Hz) together produce 6 beats in 2 seconds. When a small piece of putty is attached to tuning fork A, as in Figure 17.13, the beat frequency decreases. What is the frequency of tuning fork A before the putty is attached? (a) 378 Hz (b) 381 Hz (c) 387 Hz (d) 390 Hz

(c)387 Hz

Considering the nature of a water wave (see Figure 16.4), which of the following statements correctly describes how a fishing float moves on the surface of a lake when a wave passes beneath it? (a)It bobs up and down vertically. (b)It moves back and forth horizontally. (c)It moves in a vertical plane, exhibiting both motions described in (a) and (b) simultaneously

(c)It moves in a vertical plane, exhibiting both motions described in (a) and (b) simultaneously

Standing waves can ruin the acoustics of a concert hall if there is excessive reflection of the sound waves that the performers generate. For example, suppose that a performer generates a 2093-Hz tone. If a large-amplitude standing wave is present, it is possible for a listener to move a distance of only 4.1 cm and hear the loudness of the tone change from loud to faint. What does the distance of 4.1 cm represent? (a)One wavelength of the sound (b)One-half the wavelength of the sound (c)One-fourth the wavelength of the sound

(c)One-fourth the wavelength of the sound ( 1/4 wavelength is the distance between an antinode and an adjacent node.)

An electrically neutral object acquires a net electric charge. Which one of the following statements concerning the mass of the object is true? (a)The mass does not change. (b)The mass increases if the charge is positive and decreases if it is negative. (c)The mass increases if the charge is negative and decreases if it is positive.

(c)The mass increases if the charge is negative and decreases if it is positive.

Starting at the overlap point in Figure 17.3, you walk along a straight path that is perpendicular to the line between the speakers and passes through the midpoint of that line. As you walk, the loudness of the sound (a)changes from loud to faint to loud (b)changes from faint to loud to faint (c)does not change.

(c)does not change.

A string is vibrating back and forth as in Figure 17.15a. (1 harmonic) The tension in the string is decreased by a factor of four, with the frequency and length of the string remaining the same. A new standing wave pattern develops on the string. How many loops are in this new pattern? (a)5 (b)4 (c)3 (d)2

(d)2

When the regions of constructive and destructive interference in Figure 17.13 move past a listener's ear, a beat frequency of 2 Hz is heard. Suppose that the tuning forks in the drawing are sounded under water and that the listener is also under water. The forks vibrate at 438 and 440 Hz, just as they do in air. However, sound travels four times faster in water than in air. The beat frequency heard by the underwater listener is (a)16 Hz (b)8 Hz (c)4 Hz (d)2 Hz.

(d)2 Hz.

A positively charged particle is moving horizontally when it enters the region between the plates of a parallel plate capacitor, as the drawing illustrates. When the particle is within the capacitor, which of the following vectors, if any, are parallel to the electric field lines inside the capacitor?(a)The particle's displacement (b)Its velocity (c)Its linear momentum (d)Its acceleration

(d)Its acceleration

At an open-air rock concert you are standing directly in front of a speaker. You hear the high-frequency sounds of a female vocalist as well as the low-frequency sounds of the rhythmic bass. As you walk to one side of the speaker, the sounds of the vocalist ________, and those of the rhythmic bass ________. (a)drop off noticeably; also drop off noticeably (b)drop off only slightly; drop off noticeably (c)drop off only slightly; also drop off only slightly (d)drop off noticeably; drop off only slightly

(d)drop off noticeably; drop off only slightly

Suppose that the longitudinal wave in Figure 16.3c moves to the right at a speed of 1 m/s. Does one coil of the Slinky move a distance of 1 mm to the right in a time of 1 ms?

No. The coil moves back and forth in simple harmonic motion.

A sound wave (a periodic longitudinal wave) from a loudspeaker travels from air into water. The frequency of the wave does not change, because the loudspeaker producing the sound determines the frequency. The speed of sound in air is , 342 m/s whereas the speed in fresh water is, 1482 m/s. When the sound wave enters the water, does its wavelength increase, decrease, or remain the same?

The wavelength increases.

Blow up a balloon, tie it shut, and rub it against your shirt a number of times, so that the balloon acquires a net electric charge. Now touch the balloon to the ceiling. When released, will the balloon remain stuck to the ceiling?

Yes, because the charge on the balloon will induce a slight charge of opposite polarity in the surface of the ceiling, analogous to that in Figure 18.8.

pure tone

a sound with a single frequency

when 2 waves always meet C-to-C or R-to-R they are?

exactly in-phase and exhibit constructive interference

loudness

larger the amplitude of a wave equals a louder sound

rarefaction

region where air pressure is slightly less than normal and has inward motion

Rank the speed of sound in the follow 3 mediums: gases, liquids, and solids

solids> liquids > gases

power

the amount of energy passed per second by a sound wave E=Pt or E=IA*t

beat frequency

the number of times per second that the loudness rises and falls; is the DIFFERENCE between the two sound frequencies

Object A and object B are each electrically neutral. Two million electrons are removed from object A and placed on object B. Expressed in coulombs, what is the resulting charge (algebraic sign and magnitude) on object A and on object B?

A. +3.2*10^-13C B. -3.2*10^-13C

Carbon monoxide (CO), hydrogen (H2), and nitrogen (N2) may be treated as ideal gases. Each has the same temperature and nearly the same value for the ratio of the specific heat capacities at constant pressure and constant volume. In which two of the three gases is the speed of sound approximately the same?

CO and N2

Consider two identical, thin, and nonconducting rods, A and B. On rod A, positive charge is spread evenly, so that there is the same amount of charge per unit length at every point. On rod B, positive charge is spread evenly over only the left half, and the same amount of negative charge is spread evenly over the right half. For each rod deduce the direction of the electric field at a point that is located directly above the midpoint of the rod.

For rod A, the field points perpendicularly away from the rod. For rod B, it points parallel to the rod and is directed from the positive toward the negative half.

In Section 4.10 the concept of a massless rope is discussed. Considering Equation 16.2, would it take any time for a transverse wave to travel the length of a truly massless rope?

In Equation 16.2, the speed would be infinitely large if were zero, so it would take no time at all.

In a traveling sound wave, are there any particles that are always at rest as the wave passes by?

No, because each particle executes simple harmonic motion as the wave passes by.

Does the principle of linear superposition imply that two sound waves, passing through the same place at the same time, always create a louder sound than is created by either wave alone?

No, because if the two sound waves have the same amplitude and frequency, they might cancel in a way analogous to that illustrated in Figure 17.2b and no sound will be heard.

If two people talk simultaneously and each creates an intensity level of 65 dB at a certain point, does the total intensity level at this point equal 130 dB?

No, because it is the intensities I1 and I2 that add to give a total intensity . The intensity levels B1 and B2 do not add to give a total intensity level Btotal.

A source is emitting sound uniformly in all directions. There are no reflections anywhere. A flat surface faces the source. Is the sound intensity the same at all points on the surface?

No, because not all points on the surface are at the same distance from the source

A particle is attached to one end of a horizontal spring, and the other end of the spring is attached to a wall. When the particle is pushed so that the spring is compressed more and more, the particle experiences a greater and greater force from the spring. Similarly, a charged particle experiences a greater and greater force when pushed closer and closer to another particle that is fixed in position and has a charge of the same polarity. Considering this similarity, will the charged particle exhibit simple harmonic motion on being released, as will the particle on the spring?

No, because the force of the spring changes direction when the spring is stretched compared to when it is compressed, while the electrostatic force does not have this characteristic.

When a car is at rest, its horn emits a frequency of 600 Hz. A person standing in the middle of the street with this car behind him hears the horn with a frequency of 580 Hz. Does he need to jump out of the way?

No, because the observed frequency is less than the source frequency, so the car is moving away from him.

Examine Conceptual Example 3 before addressing this question. A wave moves on a string with a constant velocity. Does this mean that the particles of the string always have zero acceleration?

No, because the particles exhibit simple harmonic motion, in which the acceleration is not always zero.

Two cars, one behind the other, are traveling in the same direction at the same speed. Does either driver hear the other's horn at a frequency that is different from the frequency heard when both cars are at rest?

No, because there is no relative motion of the cars.

One end of each of two identical strings is attached to a wall. Each string is being pulled equally tight by someone at the other end. A transverse pulse is sent traveling along string A. A bit later an identical pulse is sent traveling along string B. What, if anything, can be done to make the pulse on string B catch up with and pass the pulse on string A?

The person pulling on string B should pull harder to increase the tension in the string.

In a thunderstorm, lightning and thunder occur nearly simultaneously. The light waves from the lightning travel at a speed of, Vlight= 3.0* 10^8 m/s, whereas the sound waves from the thunder travel at Vsound= 343 m/s. There is a rule of thumb for estimating how far away a storm is. After you see a lightning flash, count the seconds until you hear the thunder; divide the number of seconds by five to get the approximate distance (in miles) to the storm. In this rule, which of the two speeds plays a role? (a) Both Vsound and Vlight (b) Only Vsound (c) Only Vlight

a) Both Vsound and Vlight

A positive point charge +q is fixed in position at the center of a square, as the drawing shows. A second point charge is fixed to corner B, C, or D. The net electric field that results at corner A is zero. a) At which corner is the second charge located? (b) Is the second charge positive or negative? (c) Does the second charge have a greater, a smaller, or the same magnitude as the charge at the center?

a.) corner C b.) negative c.) greater

Three point charges are fixed to the corners of a square, one to a corner, in such a way that the net electric field at the empty corner is zero. Do these charges all have (a) the same sign and (b) the same magnitude (but, possibly, different signs)?

a.) no b.) no

A wire is strung tightly between two immovable posts. Review Section 12.4 and decide whether the speed of a transverse wave on this wire would increase, decrease, or remain the same when the temperature increases. Ignore any change in the mass per unit length of the wire.

decrease

when 2 waves always meet C-to-R they are?

exactly out-of-phase and exhibit destructive interference

Do you expect an echo to return to you more quickly on a hot day or a cold day, other things being equal?

hot day

A rope of mass is hanging down from the ceiling. Nothing is attached to the loose end of the rope. As a transverse wave travels upward on the rope, does the speed of the wave increase, decrease, or remain the same?

increase

Jell-O starts out as a liquid and then sets to a gel. As the Jell-O sets and becomes more solid, does the speed of sound in this material increase, decrease, or remain the same?

increase

good conductors

metals: aluminum, copper, silver, and gold

condensation

region of increased pressure that travels away from speaker at the speed of sound

ultrasonic

sound waves ABOVE 20kHz

infrasonic

sound waves BELOW 20Hz

A proton and an electron are held in place on the x axis. The proton is at x= -d, while the electron is at x=+d. They are released simultaneously, and the only force that affects their motions significantly is the electrostatic force of attraction that each applies to the other. Which particle reaches the origin first?

the electron, because, being less massive, it has the greater acceleration

good insulators

wood, plastic, rubber

Object A has a charge of, -1.6*10^-13 C and object B is electrically neutral. Two million electrons are removed from object A and placed on object B. Expressed in coulombs, what is the resulting charge (algebraic sign and magnitude) on object A and on object B?

A. +1.6*10^-13C B. -3.2*10^-13C

what is the threshold of human hearing? (ie the smallest sound intensity that the human ear can detect)

1.0*10^-12 W/m^2 ** other extreme is 1 W/M^2 can be painful and result in hearing damage

how many cycles of condensation and rarefaction are in a frequency of 1000 hz

1000 condensations and 1000 rarefactions

what is the sound range of a healthy normal person?

20Hz-20,000Hz (20kHz)

Some animals rely on an acute sense of hearing for survival, and the visible parts of the ears on such animals are often relatively large. How does this anatomical feature help to increase the sensitivity of the animal's hearing for low-intensity sounds?

Large outer ears intercept and direct more sound power into the auditory system than smaller ones do.