Questions and Answers of Inquiry into Physics

On a nice winter day at the South Pole, the temperature rises to 260° F. What is the approximate temperature in degrees Celsius?
The Fahrenheit and Celsius temperature scales agree at - 40° (- 40°C = -40°F). Do the Fahrenheit and Kelvin temperature scales ever agree? How about the Celsius and Kelvin scales?
Pyrex glassware is noted for its ability to withstand sudden temperature changes without breaking. Explain how its coefficient of linear expansion contributes to this ability.
During a workout, a shot-putter loses 0.175 kg of water through evaporation. The heat required to produce the evaporation (a phase change from liquid water to water vapor) comes from the athlete’s
A copper vat is 10 m long at room temperature (20oC). How much longer is it when it contains boiling water at 1 atm pressure?
What happens to the atoms and molecules in a substance as its temperature increases?
What is the significance of absolute zero?
Air molecules in a warm room (27°C = 300 K) typically have speeds of about 500 m/s (1,100 mph). Why is it that we are unaware of these fast-moving particles continuously colliding with our bodies?
If air at 35°C and 77 percent relative humidity is cooled to 25°C, what mass of water would condense out of the air in a room that measures 5 m by 4 m by 3 m?
Is our society truly facing an “energy crisis,” assuming by this term we mean that we are running out of energy? What is happening to our energy resources as a result of the increasing
Six insulated containers hold 1500 g of water at 24°C. A small copper cylinder is placed in each cup; the masses and initial temperatures of the cylinders vary as given below. Rank the containers
Six cylinders each contain the same mass of helium gas but have different volumes and temperatures as given below. All of the containers are made of the same material and stored under the same
Five Carnot engines operate between reservoirs with temperatures Th and Tl as given below. Rank these engines according to their efficiency from most efficient to least efficient. If any of the
At one moment during a storm, the electric field between two clouds is directed toward the east. What is the direction of the force on any electron in this region? What is the direction of the force
Using your understanding of the nature of internal energy and temperature, explain why we might expect the resistance of a solid to increase if its temperature increases.
What remains after a hydrogen atom is positively ionized?
A particular solid is electrically charged after it is rubbed, but it is not known whether its charge is positive or negative. How could you determine which charge it has by using a piece of plastic
All matter contains both positively and negatively charged particles. Why do most things have no net charge?
In otherwise empty space, what would happen if the size of the electrostatic force acting between two positively charged objects was exactly the same as that of the gravitational force acting between
Imagine a company offering a line of hair dryers that operate on different voltages, say, 12, 30, 60, and 120 V. Assume that all of the dryers are rated at 1,200 W and find the current that would
When clothes are removed from a hot dryer, they often cling together, but when two identical articles of clothing, such as two matched socks, are taken out, they usually repel one another. Explain
Describe the similarities and the differences between the gravitational force between two objects and the electrostatic force between two charged objects.
The current that flows through an incandescent lightbulb immediately after it is turned on is higher than the current that flows moments later. Why?
The resistance of the skin on a person’s finger is typically about 20,000 V. How much voltage would be needed to cause a current of 0.001 A to flow into the finger?
Give an example of a wave that does not need a medium in which to travel and a wave that does need a medium.
A popular distraction in large crowds at sporting events since the 1980s is the “wave.” People in one section quickly stand up and raise their arms and then sit down; people in the neighboring
The speed of an aircraft is sometimes expressed as a Mach number: Mach 1 means that the speed is equal to the speed of sound. If you wish to determine the speed of an aircraft going Mach 2.2, for
Explain the process of echolocation. How is the Doppler effect sometimes incorporated?
In the past, ships often carried small cannons that were used when approaching shore in dense fog to estimate the distance to the hidden land. Explain how this might have been done.
You can buy a measuring device billed as a “sonic tape measure.” Describe how a device equipped with an (ultrasonic) speaker, a microphone, and a precision timer could be used to measure the
While a shock wave is being generated by a moving wave source, is the Doppler effect also occurring? Explain.
Describe some of the things that would happen if the speed of sound in air suddenly decreased to, say, 20 m/s. What would it be like living next to a freeway?
A recording of a high-frequency pure tone is played through both speakers of a portable stereo placed in an open field. A person a few meters in front of the stereo walks slowly along an arc around
When a wave passes through two nearby gaps in a barrier, interference will occur, provided that there is also diffraction. Why must there be diffraction?
If a boat is producing a bow wave as it moves over the water, what must be true about its speed?
As a loud, low-frequency sound wave travels past a small balloon, the balloon’s size is affected. Explain what happens.
Approximately how many times louder is a 100-dB sound than a 60-dB sound?
Describe the wave forms of pure tones, complex tones, and noise.
What is ultrasound? Give two examples of what it can be used for.
The frequency of the highest note on the piano is 4,186 Hz. (a) How many harmonics of that note can we hear? (b) How many harmonics of the note one octave below it can we hear?
Describe how sound is produced in string instruments. Why does tightening a string change the frequency of the sound it makes?
A conditioning drill consists of repeatedly running from one end of a basketball court to the other, turning around and running back. Sometimes the drill is changed and the runner turns around at
What is reverberation? How does reverberation affect how we hear sounds?
What are the three categories used to describe our mental perception of a sound? On what physical properties of sound waves does each depend?
A 100-Hz pure tone at a 70-dB sound level and a 1,000-Hz pure tone at the same sound level are heard separately. Do they sound equally loud? If not, which is louder, and why?
A sound is produced by combining three pure tones with frequencies of 200 Hz, 400 Hz, and 600 Hz. A second sound is produced using 200 Hz, 413 Hz, and 600 Hz pure tones. What important difference is
The highest musical note on the piano has a frequency of 4,186 Hz. Why would a tape of piano music sound terrible if played on a tape player that reproduces frequencies only up to 5,000 Hz?
Normal telephones do not transmit pure tones with frequencies below about 300 Hz. But a person whose speaking voice has a frequency of 100 Hz can be heard and understood over the phone. Why is that?
A special room contains a mixture of oxygen and helium that is breathable. Two musicians play a guitar and a flute in the room. Does each instrument sound different from when it is played in normal
An audio speaker producing a steady sound at an outdoor concert is 25 ft away from you. If you move to a position where the speaker is 75 ft distant, by what factor will the amplitude of the sound
Six transverse waves move through different media. They all have the same frequency, but their amplitudes, A, and wavelengths, λ, vary as indicated. Rank these waves according to their propagation
Six strings, all having the same lengths, are stretched taut between two fixed points. The tensions, F, and masses, m, of the strings vary as shown. A transverse pulse with a given amplitude is
A solid metal cylinder has a certain resistance. It is then heated and carefully stretched to form a longer, thinner cylinder. After it cools, will its resistance be the same as, greater than, or
An electric train operates on 750 V. What is its power consumption when the current flowing through the train’s motor is 2,000 A?
A student using a sensitive meter that measures resistance finds that the resistance of a thin wire is changed slightly when it is picked up with a bare hand. What causes the change in the
If a new material is found that is a superconductor at all temperatures, what parts of some common electric devices would definitely not be made out of it? Explain.
Your cell phone typically consumes about 400 mW of power when you text a friend. If the phone is operated using a lithium-ion battery with a voltage of 3.6 V, what is the current flowing through the
Explain what current, resistance, and voltage are.
Make a sketch of a simple electric circuit and label the key elements in the circuit.
Describe Ohm’s law.
A power supply is connected to two bare wires that are inserted into a glass of saltwater. The resistance of the water decreases as the voltage is increased. Sketch a graph of the voltage versus the
A clock consumes 2 W of electrical power. How much energy does it use each day?
There are two basic methods for connecting more than one electrical device in a circuit. Name, describe, and give the advantages of each.
Make a sketch of an electric circuit that contains a switch and two lightbulbs connected in such a way that if either bulb burns out the other still functions, but if the switch is turned off, both
A representative lightning strike is caused by a voltage of 200,000,000 V and consists of a current of 1,000 A that flows for a fraction of a second. Calculate the power.
Two 1.5-volt batteries are connected in series in an electric circuit. Use the concept of energy to explain why this combination is equivalent to a single 3-volt battery. When connected in parallel,
An electrical supply company sells two models of 100-watt power supplies (the maximum power output is 100 W), one with an output of 12 V and the other 6 V. What can you conclude about the maximum
A certain electric motor draws a current of 10 A when connected to 120 V.(a) What is the motor’s power consumption?(b) How much energy does it use during 4 h of operation? Express the answer in
A simple electric circuit consists of a constant-voltage power supply and a variable resistor. What effect does reducing the resistance have on the current in the circuit and on the power output of
What is the purpose of having fuses or circuit breakers in electric circuits? How should they be connected in circuits so they will be effective?
A lightbulb is rated at 60 W when connected to 120 V.(a) What current flows through the bulb in this case?(b) What is the bulb’s resistance?(c) What would be the current in the bulb if it were
A 20-A fuse in a household electric circuit burns out. What catastrophe could occur if it is replaced by a 30-A fuse?
Why is it economical to use extremely high voltages for the transmission of electrical power?
A simple circuit of the form shown in Figure 7.37 is constructed using a battery and three lightbulbs. The bulbs may have different resistances as given in the six circumstances A through F. For each
Rank the force on each of the point charges q1 and q2 in the following pairings from most attractive to most repulsive. The separation, d, between each pair is given. Explain the reasoning you used
Six resistors, all having the same temperatures and compositions, are each attached to a battery with voltage V to form a simple circuit. The resistors have different lengths, l, but the same
Saltwater contains an equal number of positive and negative ions. When saltwater is flowing through a pipe, does it constitute an electric current?
Materials can be classified into four categories based on the ease with which charges can flow through them. Give the names of these categories and describe each one.
An electric car is being designed to have an average power output of 4,000 W for 2 h before needing to be recharged. (Assume there is no wasted energy.)(a) How much energy would be stored in the
Explain what AC and DC are. Why is AC used by electric utilities? Why is DC used in flashlights?
If AC in a circuit can be thought of as a wave, which kind is it, longitudinal or transverse?
If the electric utility company where you live suddenly changed the frequency of the AC to 20 Hz, what problems might this cause?
What happens to a ferromagnetic material when it is placed in a magnetic field? What causes magnetic declination? Is there a place where the magnetic declination is 1808 (a compass points south)? If
A solenoid connected to a 60-Hz AC source will produce an oscillating magnetic field, as we have seen. If a permanent magnet is inserted into the solenoid, it will oscillate, but not with the same
What is the wavelength of the 60,000-Hz radio wave used by “radio-controlled” clocks and wristwatches?
Describe the three basic interactions between electricity and magnetism.
Explain what superconducting electromagnets are. What advantages do they have over conventional electromagnets?
Sketch a diagram of an atom with one electron orbiting the nucleus. Use the right-hand rule to determine the direction of the magnetic field produced by the electron.
The wavelength of an electromagnetic wave is measured to be 600 m.(a) What is the frequency of the wave?(b) What type of EM wave is it?
What disadvantages do they have?
If a coil of wire is connected to a very sensitive ammeter and then waved about in the air, a current will be induced in it even if there are no magnets around. Why?
Name five different basic devices that use at least one of the electromagnetic interactions.
Even though the output voltage of a transformer can be much larger than the input voltage, the power output is nearly the same as the power input. Use this to determine the relationship between the
A piece of iron is heated with a torch to a temperature of 900 K. How much more energy does it emit as blackbody radiation at 900 K than it does at room temperature, 300 K?
In many cases, the effect of an electromagnetic interaction is perpendicular to its cause. Describe two different examples that illustrate this.
The highest frequency sound that can be recorded by a tape recorder depends on the size of the gap in the recording head. Why? Would a wider or a narrower gap be capable of recording higher
To test whether a material is a superconductor, a scientist decides to make a ring out of the material and then to see whether a current will flow around in the ring with no steady energy input.(a)
Describe what happens to an electric charge as an electromagnetic wave passes through the region around it. Explain why the charge will produce another electromagnetic wave.
A rectangular metal plate measures 0.15 m long and 0.1 m wide. The plate is heated to a temperature of 1,200 K by passing a current through it. Assuming that it behaves like a blackbody, how much
A coil of wire has a large alternating current flowing in it. A piece of aluminum or copper placed near the coil becomes warm even if it does not touch the coil. Explain why.

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