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the physical universe

Questions and Answers of The Physical Universe

Explain why lines of force can never cross one another.
Why is a piece of iron attracted to either pole of a magnet?
A 1.35-V mercury cell with a capacity of 1.5 A · h is used to power a cardiac pacemaker. (a) If the power required is 0.1 mW (1 mW = 1 milliwatt = 0.001 W), what is the average current?(b) How
A 240-V clothes dryer draws a current of 15 A. How much energy, in kilowatt-hours and in joules, does it use in 45 min of operation?
A transformer whose primary coil has twice as many turns as its secondary coil is used to convert 240-V ac to 120-V ac. If the current in the secondary coil is 4 A, the primary current isa. 1 Ab. 2
If your home has a 120-V power line, how much power in watts can you draw from the line before a 30-A fuse will burn out? How many 100-W lightbulbs can you put in the circuit before the fuse will
A 240-V, 1-kW electric heater is mistakenly connected to a 120-V power line that has a 15-A fuse. The heater willa. give off less than 1 kW of heatb. give off 1 kW of heatc. give off more than 1 kW
A 120-V, 1-kW electric heater is mistakenly connected to a 240-V power line that has a 15-A fuse. The heater willa. give off less than 1 kW of heatb. give off 1 kW of heatc. give off more than 1 kW
An electric drill rated at 400 W is connected to a 240-V power line. How much current does it draw?
A car’s storage battery is being charged at a rate of 75 W. If the potential difference across the battery’s terminals is 13.6 V, charge is being transferred between its plates ata. 0.18 C/sb.
The current in a 40-W, 120-V electric light bulb isa. 1/3 Ab. 3 Ac. 80 Ad. 4800 A
(a) If a 75-W lightbulb is connected to a 120-V power line, how much current flows through it? (b) What is the resistance of the bulb?
The resistance of a lightbulb that draws a current of 2 A when connected to a 12-V battery isa. 1.67 Ωb. 2 Ωc. 6 Ωd. 24 Ω
The voltage needed to produce a current of 5 A in a resistance of 40 Ω isa. 0.125 Vb. 5 Vc. 8 Vd. 200 V
How are the terminals of a set of batteries connected when the batteries are in series? In parallel? What is the advantage of each combination?
When the voltage across a certain resistance is V, the power delivered is P. If the voltage is doubled to 2V, the power delivered becomesa. 2Pb. 4Pc. P2d. 4P2
Five joules of work are needed to shift 10 C of charge from one place to another. The potential difference between the places isa. 0.5 Vb. 2 Vc. 5 Vd. 10 V
Should a fuse be connected in series or in parallel with the circuit it is meant to protect? Why?
The force between two charges of −3 × 10−9 C that are 5 cm apart isa. 1.8 × 10−16 Nb. 3.6 × 10−15 Nc. 1.6 × 10−6 Nd. 3.2 × 10−5 N
A positive and a negative charge are initially 4 cm apart.When they are moved closer together so that they are now only 1 cm apart, the force between them isa. 4 times smaller than beforeb. 4 times
What potential difference must be applied across a 1500-Ω resistance in order that the resulting current be 50 mA (1 mA = 1 milliampere = 0.001 A)?
If 105 electrons are added to a neutral object, its charge will bea. −1.6 × 10−24 Cb. −1.6 × 10−14 Cc. +1.6 × 10−24 Cd. +1.6 × 10−14 C
A transformer can changea. the voltage of an alternating currentb. the power of an alternating currentc. alternating current to direct currentd. direct current to alternating current
How much current is drawn by a 240-V water heater whose resistance is 24 Ω?
The alternating current in the secondary coil of a transformer is induced bya. the varying electric field of the primary coilb. the varying magnetic field of the primary coilc. the varying magnetic
A generator is said to “generate electricity.” What it actually does is act as a source ofa. electric chargeb. electronsc. magnetismd. electric energy
The potential difference between a cloud and the ground is 4 MV. A charge of 200 C is transferred in a lightning stroke between the cloud and the ground. How much energy is dissipated?
The nature of the force that is responsible for the operation of an electric motor isa. electricb. magneticc. a combination of electric and magneticd. either electric or magnetic, depending on the
An electromagneta. uses an electric current to produce a magnetic fieldb. uses a magnetic field to produce an electric currentc. is a magnet that has an electric charged. operates only on alternating
(a) The capacity of a battery is usually quoted in amperehours. Of what is this quantity a unit? (b) How much energy is stored in a 6-V battery rated at 20 A · h?
A current-carrying wire is in a magnetic field with the direction of the current the same as that of the field.a. The wire tends to move parallel to the field.b. The wire tends to move perpendicular
A magnetic field does not interact with aa. stationary electric chargeb. moving electric chargec. stationary magnetd. moving magnet
What basic aspect of superconductivity has prevented its large-scale application thus far?
The magnetic field lines around a long, straight current carrying wire area. straight lines parallel to the currentb. straight lines that radiate from the current like spokes of a wheelc. concentric
The magnetic field shown in Fig. 6-50 is produced bya. two north polesb. two south polesc. a north pole and a south poled. a south pole and an unmagnetized iron bar
The magnetic field of a bar magnet resembles most closely the magnetic field ofa. a straight wire carrying a direct currentb. a straight wire carrying an alternating currentc. a wire loop carrying a
One terminal of a battery is connected to a lightbulb. What, if anything, happens?
A moving electric charge producesa. only an electric fieldb. only a magnetic fieldc. both an electric and a magnetic fieldd. any of these, depending on its speed
In a drawing of magnetic field lines, the weaker the field is, thea. closer together the field lines areb. farther apart the field lines arec. more nearly parallel the field lines ared. more
How far apart are two charges of +1 × 10−8 C that repel each other with a force of 0.1 N?
Magnetic field lines provide a convenient way to visualize a magnetic field. Which of the following statements is not true?a. The path followed by an iron particle released near a magnet corresponds
The force on an electron that moves in a curved path must bea. gravitationalb. electricalc. magneticd. one or more of these
(a) A metal sphere with a charge of +1 × 10−5 C is 10 cm from another metal sphere with a charge of −2 × 10−5 C. Find the magnitude of the attractive force acting on each sphere. (b) The
All magnetic fields originate ina. iron atomsb. permanent magnetsc. stationary electric chargesd. moving electric charges
When a magnetized bar of iron is strongly heated, its magnetizationa. becomes weakerb. becomes strongerc. reverses its directiond. is unchanged
Two charges originally 80 mm apart are brought together until the force between them is 16 times greater. How far apart are they now?
The electric energy lost when a current passes through a resistancea. becomes magnetic energyb. becomes potential energyc. potential difference ohmd. power watt
Electric power is equal toa. (current)(voltage)b. current/voltagec. voltage/currentd. (resistance)(voltage)
A charge of +3 × 10−9 C is 50 cm from a charge of −5 × 10−9 C. Find the magnitude and direction of the force on each charge.
Match each of the electrical qualities listed below with the appropriate unit from the list on the right:a. resistance ..................... voltb. current ............................ amperec.
Superconductorsa. have no electrical resistanceb. have very little electrical resistancec. are used in making transistorsd. have no practical applications
A solid conductor is onea. whose electrons are firmly bound in placeb. whose electrons are free to move aboutc. that has no electronsd. that has too many electrons
An object has a positive electric charge whenevera. it has an excess of electronsb. it has a deficiency of electronsc. the nuclei of its atoms are positively chargedd. the electrons of its atoms are
When two objects attract each other electrically, must both of them be charged? When two objects repel each other electrically, must both of them be charged?
The particle easiest to remove from an atom is a (an)a. electronb. protonc. neutrond. nucleus
An atom consists of aa. uniform distribution of positive charge in which electrons are embeddedb. uniform distribution of negative charge in which electrons are embeddedc. small negative nucleus
Find the total charge of 1 g of protons.
The electric force between a proton and an electrona. is weaker than the gravitational force between themb. is equal in strength to the gravitational force between themc. is stronger than the
Coulomb’s law for the force between electric charges belongs in the same general category asa. the law of conservation of energyb. Newton’s second law of motionc. Newton’s law of gravitationd.
Nearly all the mass of an atom is concentrated in its nucleus. Where is its charge located?
Protons and electrons have different masses. When they are the same distance apart, the electric force between two electronsa. is less than the force between two protonsb. is the same as the
A positively charged rod is brought near an isolated metal ball. Which of the sketches in Fig. 6-49 best illustrates the arrangement of charges on the ball? a. (a)b. (b)c. (c)d. (d) (a) (b) (c) (d)
A plastic ball has a charge of +10−12 C. (a) Does the ball have more electrons or fewer electrons than when it is electrically neutral? (b) How many such electrons?
A positive electric chargea. attracts other positive chargesb. repels other positive chargesc. does not interact with other positive charges but only with negative onesd. consists of an excess of
The charge on an electrona. is 1 Cb. depends on the electron’s massc. depends on the electron’s sized. is always the same
What reasons might there be for the universal belief among scientists that there are only two kinds of electric charge?
The evolution of today’s animals from their primitive ancestors of billions of years ago represents a large increase in order, which corresponds to a decrease in entropy. How can this be reconciled
Surface water in a tropical ocean is typically at 27°C whereas at a depth of a kilometer or more it is at only about 5°C. It has been proposed to operate heat engines using surface water as the hot
An engine that operates between 2000 K and 700 K has an efficiency of 40 percent. What percentage of its maximum possible efficiency is this?
The first law of thermodynamics is the same as the law of conservation of energy. Is there any law of nature that is the same as the second law of thermodynamics?
In another attempt to cool the kitchen, the person leaves the refrigerator door open, again with the kitchen door and windows closed. Now what will happen?
The oceans contain an immense amount of heat energy. Why can a submarine not make use of this energy for propulsion?
Water at 50°C can be obtained by mixing together which one or more of the following? Which of the others would have final temperatures higher than 50°C and which lower than 50°C?a. 1 kg of ice at
Solar energy arrives at a rate of 1.2 kW at a reflecting dish with an area of 1 m2 that focuses the light on a jar that contains 100 g of water initially at 20°C. How long will it take the water to
A total of 500 kJ of heat are added to 1 kg of water at 20°C. What is the final temperature of the water? If it is 100°C, how much steam, if any, is produced?
Give as many methods as you can think of that will increase the rate of evaporation of a liquid sample. Explain why each method will have this effect.
Why does blowing across hot coffee cool it down?
What is the advantage of installing the heating element of an electric kettle near its bottom?
Outdoors in winter, why does the steel blade of a shovel feel colder than its wooden handle?
A mixture of the gases hydrogen and carbon dioxide (CO2) is at 20°C. A CO2 molecule has about 22 times the mass of a hydrogen molecule, whose average speed at 20°C is about 1.6 km/s. What is the
To what temperature must a gas sample initially at 27°C be raised in order for the average energy of its molecules to double?
How can the conclusion of kinetic theory that molecular motion occurs in solids be reconciled with the observation that solids have definite shapes and volumes?
When they are close together, molecules attract one another slightly. As a result of this attraction, are gas pressures higher or lower than expected from the ideal gas law?
At absolute zero, a sample of an ideal gas would have zero volume. Why would this not be true of an actual gas at absolute zero?
Is it meaningful to say that an object at a temperature of 200°C is twice as hot as one at 100°C?
An air tank used for scuba diving has a safety valve set to open at a pressure of 28 MPa. The normal pressure of the full tank at 20°C is 20 MPa. If the tank is heated after being filled to 20 MPa,
To what Celsius temperature must a gas sample initially at 20°C be heated if its volume is to double while its pressure remains the same?
An oxygen cylinder used for welding contains 40 L of oxygen at 20°C and a pressure of 17 MPa. The density of oxygen is 1.4 kg/m3 at 20°C and atmospheric pressure of 101 kPa. Find the mass of the
A certain quantity of hydrogen occupies a volume of 1000 cm3 at 0°C (273 K) and ordinary atmospheric pressure. (a) If the pressure is tripled but the temperature is held constant, what will the
A 200-L iron tank has a mass of 36 kg.(a) Will it float in seawater when empty? (b) When filled with freshwater? (c) When filled with gasoline?
A raft 3 m long, 2 m wide, and 30 cm thick, made from solid balsa wood, is floating in a freshwater lake. How many 65-kg people can it support?
How much force is needed to support a 100-kg iron anchor when it is submerged in seawater? (First find the anchor’s volume.)
A sailboat has a lead or iron keel to keep it upright despite the force wind exerts on its sails. What difference, if any, is there between the stability of a sailboat in freshwater and in seawater?
If a heat engine that exhausts heat to a reservoir at 400 K is to have an efficiency of 33 percent, it must take in heat from a source at a minimum ofa. 133 Kb. 449 Kc. 532 Kd. 600 K
An ideal frictionless engine absorbs heat from a source at 400 K and exhausts heat to a reservoir at 300 K. Its efficiency isa. 25 percentb. 33 percentc. 75 percentd. 133 percent
A ship catches fire, and its steel hull expands as it heats up. What happens to the volume of water the ship displaces? What happens to the height of the ship’s deck above the water?
At which of the following temperatures would the molecules of a gas have twice the average kinetic energy they have at room temperature, 20°C?a. 40°Cb. 80°Cc. 313°Cd. 586°C
Lead melts at 330°C. On the absolute scale this temperature corresponds toa. 57 Kb. 362 Kc. 571 Kd. 603 K
A wooden block is submerged in a tank of water and pressed down against the bottom of the tank so that there is no water underneath it. The block is released. Will it rise to the surface or stay
If the pressure on 10 m3 of air is increased from 200 kPa to 800 kPa, the new volume of air will bea. 1.25 m3b. 1.67 m3c. 2.5 m3d. 40 m3

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