physics exam #3

A heater uses 20 A when used in a 110-V line. If electric power costs 10 cents per kilowatt hour, the cost of running the heater for 10 hours is $5.50. $0.22. $2.20. $0.55. none of these

$2.20

Calculate the power of a device that carries 0.42 A when impressed with 130 V . Power= I x V

P= 55 W

Rearrange the equation current = voltage/resistance to express resistance in terms of current and voltage. Then solve the following: A certain device in a 80-V circuit has a current rating of 30 A . What is the resistance of the device (how many ohms)?

R = 2.7 Ω

(use above) Then, using the equation current = voltage/resistance, find the resistance of the toaster.

R = 5.9 Ω

A step-up transformer has a ratio of one to ten. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is 1000 W. 100 W. 1 W. 10 W. none of these

100 W

Three resistors, 1-ohm, 2-ohm, and 3- ohm are connected in parallel. If they were connected in series instead their equivalent resistance would be 7 times as great. 13 times as great. 9 times as great. 11 times as great. None of the above choices are correct.

11 times as great

In a 110-volt circuit containing a lamp in series with the voltage source 110 joules of energy are shared among all the coulombs in the circuit at any instant. 110 joules of energy are given up by each coulomb of charge making up the current in the circuit. 110 coulombs of charge flow through the lamp every second. 110 joules of energy are converted to heat and light in the circuit every second. none of the above

110 joules of energy are given up by each coulomb of charge making up the current in the circuit.

A power line with a resistance of 2 ohms has a current of 80 A in it. The power dissipated in the line is 40 W. 160 W. 12,800 W. 320 W. none of these

12,800 W

A 4-ohm resistor is connected in parallel with a 6-ohm resistor. This combination produces an equivalent resistance of 4 ohms. 2.4 ohms. 5 ohms. 5.5 ohms. 10 ohms.

2.4 ohms

An electric heater is rated at 300 W when used in a 110-V circuit. The safety fuse in the circuit can handle 15 A of current. How many heaters can be safely operated in the circuit? 2 4 more than 5 5 3

5

A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in the secondary coil is 5 A. 25 A. 10 A. 2 A. none of these

5 A

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

5 ohms

The voltage across the input terminals of a transformer is 110 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer puts out is 220 V. 110 V. 55 V. 25 V. none of these

55 V

A certain radar installation tracks airplanes by transmitting electromagnetic radiation of wavelength 2.2 cm . Find the frequency of this radiation Find the time required for a pulse of radar waves to reach an airplane 5.4 km away and return.

a) f= 14 GHz b) t = 3.6 x 10^-5 s

Calculate the current in the 340-Ω filament of a bulb connected to a 160-V line. Ohm ' s Law: I=V/R

I = 0.47 A

The wattage marked on a lightbulb is not an inherent property of the bulb, but depends on the voltage to which it is connected, usually 110 or 120 V. How many amperes flow through a 70-W bulb connected in a 120-V circuit?

I = 0.58 A

Given that the power consumed by a device is 1700 W operating on a 160-V line, calculate the amount of current it draws. power= I x V

I = 11A

Using the formula power = current × voltage, find the current drawn by a 1700-W toaster connected to 100 V .

I = 17 A

Calculate the current that moves through your fingers (resistance 1300 Ω ) when you touch them to the terminals of a 6.4-V battery. Ohm ' s Law: I=V/R

I = 4.9×10−3 A

A model electric train requires 6.0 V to operate. If the primary coil of its transformer has 240 windings, how many windings should the secondary have if the primary is connected to a 120-V household circuit?

N = 12 windings

Neon signs require about 10800 V for their operation. What should be the ratio of the number of loops in the secondary to the number of loops in the primary for a neon-sign transformer that operates from 120-V lines?

N2/ N1 = 90

In a common dc circuit, electrons move at speeds of a fraction of a centimeter per second. the speed of light. the speed of a sound wave. many centimeters per second. none of these

a fraction of a centimeter per second

At the same time an astronaut on the moon sees a solar eclipse, observers on Earth see a solar eclipse. no eclipse at all. a lunar eclipse.

a lunar eclipse

Which of the following cannot travel in a vacuum? a radio wave a sound wave a light wave All can travel in a vacuum. None can travel in a vacuum.

a sound wave

An ideal transformer has 40 turns in its primary and 300 turns in its secondary. 9.0 V ac is connected to the primary. Find the volts ac available at the secondary. Find the current in a 10-Ω device connected to the secondary. How much power is supplied to the primary?

a) V2 = 68 V b) I = 6.8 A c)P1 = 460 W

The source of all electromagnetic waves is changes in atomic energy levels. crystalline fluctuations. vibrating atoms. accelerating electric charges. none of these

accelerating electric charges

When there is a change in the magnetic field in a closed loop of wire electromagnetic induction occurs. a current is created in the loop of wire. a voltage is induced in the wire. all of these none of these

all of these

The field surrounding every moving electron is always both electric and magnetic. sometimes magnetic and sometimes electric. always electric but never magnetic. always magnetic but never electric. none of the above

always both electric and magnetic

A helium-neon laser emits light of wavelength 633 nanometers (nm). Light from an argon laser has a wavelength of 515 nm. Which laser emits the higher-frequency light? a helium-neon laser an argon laser

an argon laser

Moving electric charges will interact with an electric field or a magnetic field. only an electric field. only a magnetic field. none of these

an electric field or a magnetic field

An electric motor is very similar to a radio receiver. an electric generator. an automobile battery. None of the above choices are correct.

an electric generator

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

at right angles to the direction of the field

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

at right angles to the direction of the motion

The source of electrons lighting an incandescent ac light bulb is atoms in the light bulb filament. the wire leading to the lamp. the power company. the source voltage. electrical outlet.

atoms in the light bulb filament

Like kinds of magnetic poles repel while unlike kinds of magnetic poles repel also. may attract or repel. attract.

atract

A capacitor is used to store energy. charge. both charge and energy. neither charge nor energy.

both

A 60-W light bulb and a 100-W light bulb are connected in series to a 120 V outlet. Which light bulb has more current in it? the 60-W bulb the 100-W bulb Both have the same current.

both have the same current

Rainbows exist because light is reflected. refracted. both of these neither of these

both of these

Thrust a magnet into a coil of wire and the coil has a current in it. becomes an electromagnet. both of these neither of these

both of these

Which travels faster through a vacuum - an infrared ray or a gamma ray? an infrared ray a gamma ray Both travel at the same speed c.

both travel at the same speed c

If a light signal and a radio signal were emitted simultaneously from Alpha Centauri, the first to reach Earth would be the light signal. radio signal. both would reach Earth at the same time.

both would reach earth at the same time

When the pinhole in a pinhole camera is made larger, the image is brighter. clearer. both neither

brighter

Transformers use ac so there will be the required voltage for transformation. change in magnetic field for operation. transfer of energy from coil to coil. change in input current. magnetic field intensities.

change in magnetic field for operation

Magnetism is due to the motion of electrons as they move around the nucleus. spin on their axes. Choices A and B are both correct. None of the above choices are correct.

choices A and B are both correct

Voltage can be induced in a wire by moving the wire near a magnet. changing the current in a nearby wire. moving a magnet near the wire. Choices A, B, and C are all true. None of the above choices are true.

choices A, B, and C are all true

Magnetic field lines about a current-carrying wire extend radially from the wire. circle the wire in closed loops. Choices A and B are both correct. None of the above choices are correct.

circle the wire in closed loops

As more lamps are put into a series circuit, the overall current in the power source increases. decreases. stays the same.

decreases

An electron is shot through a spot somewhere between the ends of a horseshoe magnet. The electron direction is changed. speed is increased. is attracted to one of the poles, and repelled by the other. is repelled by both poles, and therefore is turned back. is unaffected by the field.

direction is changed

Metal detectors, like the ones used at airports, are activated by electromagnetic induction. alternating current. magnetic fields. electric fields.

electromagnetic induction

Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is relatively small. equally huge. More information is needed.

equally huge

Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is at or about 50 N. exactly 100 N. More information is needed.

exactly 100 N

A circuit breaker often serves the same purpose as a capacitor. fuse. battery All of the above choices are correct. None of the above choices are correct.

fuse

A device that transforms mechanical energy into electrical energy is a motor. generator. transformer. magnet. none of these

generator

Alternating current is normally produced by a generator. battery. both of these neither of these

generator

Two lamps, one with a thick filament and one with a thin filament of the same material, are connected in series to a battery. The voltage is greater across the lamp with the thick filament. greater across the lamp with the thin filament. the same for both lamps.

greater across the lamp with the thin filament

If a compass is moved from the northern hemisphere to the southern hemisphere, its magnetic needle will change direction by 180 degrees. by 90 degrees. hardly at all. depending on where the measurement is taken. none of these

hardly at all

Heat a copper wire and its electric resistance decreases. remains unchanged. increases.

increases

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

increases

Magnetic domains normally occur in silver. iron. copper. all of these none of these

iron

Things seen by moonlight usually aren't colored because moonlight photons don't have enough energy to activate the retina's cones. is too dim to activate the retina's cones. doesn't have very many colors in it. all of these none of these

is too dim to activate the retinas cones

Two lamps, one with a thick filament and one with a thin filament of the same material, are connected in parallel to a battery. The current is the same in both lamps. larger in the lamp with the thick filament. larger in the lamp with the thin filament.

larger in the lamp with the thick filament

Compared to the primary voltage, the secondary voltage may be smaller. the same. larger. the same or smaller, but not larger. larger, smaller, or the same.

larger, smaller, or the same

A 100-Watt lamp glows brighter than a 25-Watt lamp. The electrical resistance of the 100-Watt lamp must be greater. the same. less.

less

Compared to a single lamp connected to a battery, two identical lamps connected in series to the same battery will carry less current. the same current. more current.

less current

When a light switch is turned on in a dc circuit, the average speed of electrons in the lamp is the speed of light. 1000 cm/s. dependent on how quickly each electron bumps into the next electron. less than 1 cm/s. the speed of sound waves in metal.

less than 1 cm/s

The main difference between a radio wave and a sound wave is their different frequencies. modes of travel. wavelengths. energies. amplitudes.

modes of travel

What is the wavelength of an electromagnetic wave that has a frequency of 1 hertz? more than 1 m less than 1 m 1 m

more than 1 m

When two lamps are connected in series to a battery, the electrical resistance that the battery senses is less than the resistance of either lamp. more than the resistance of either lamp. none of these

more than the resistance of either lamp

The source of all magnetism is tiny domains of aligned atoms. tiny pieces of iron. ferromagnetic materials. moving electric charge. none of these

moving electric charge

A step-up transformer increases energy. power. both power and energy. neither power or energy.

neither

What condition must exist between two points in a conductor in order to maintain a flow of charge? a switch connected in series a steady magnetic field a high resistance All of the above choices are correct. None of the above choices are correct

none of the above choices are correct

What is the resistance of a 120-W incandescent lamp connected to a 120-V power supply? 1 ohm 100 ohms 144 ohms 60 ohms none of these

none of these

An iron nail is more strongly attracted to the north or south pole - no difference really. south pole of a magnet. north pole of a magnet.

north or south pole- no difference really

Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a north pole. north or south pole - no difference really. south pole.

north pole

Which pole of a compass needle points to a south pole of a magnet? south pole north pole both of these

north pole

Outside a magnet, magnetic field lines are conventionally drawn from north to south. south to north. either way

north to south

If the primary of a transformer were connected to a dc power source, the transformer would have a voltage output that is also dc. only while being connected or disconnected. at a higher efficiency than with an ac source. the same. none of these

only while being connected or disconnected

The headlights, radio, and defroster fan in an automobile are connected in series with a switch for each. parallel without separate switches. series without separate switches. parallel with a switch for each.

parallel with a switch for each

The force on an electron moving in a magnetic field will be the largest when its direction is at an angle other than 90 degrees to the magnetic field direction. exactly opposite to the magnetic field direction. the same as the magnetic field direction. perpendicular to the magnetic field direction. none of these

perpendicular to the magnetic field direction

When a bar magnet is thrust into a coil of copper wire, the coil tends to repel the magnet as it enters. attract the magnet as it enters. both of these neither of these

repel the magnet as it enters

Short wavelengths of visible light interact more frequently with the atoms in glass than do longer wavelengths. Does this interaction time tend to speed up or to slow down the average speed of short-wavelength light in glass? speed up slow down

slow down

Which of the following is fundamentally different from the others? gamma rays X-rays sound waves radio waves light waves

sound waves

Find the time for a pulse of laser light to reach the Moon and to bounce back to Earth.

t = 2.6 s

The nearest star beyond the Sun is Alpha Centauri, 4.2×10^16m away. If we were to receive a radio message from this star today, find the time when it would have been sent.

t = 4.4 years ago

The total charge that an automobile battery can supply without being recharged is given in terms of ampere-hours. A typical 12-V battery has a rating of 60 ampere-hours (60 A for 1 h, 30 A for 2 h, and so on). Suppose that you forget to turn the headlights off in your parked automobile. If each of the two headlights draws 2.5 A , how long will it be before your battery is "dead"?

t= 12 h

A proton moves in a circular path perpendicular to a constant magnetic field. If the field strength of the magnet is increased, does the diameter of the circular path increase, decrease, or remain the same? The diameter of the circular path increases. The diameter of the circular path decreases. The diameter of the circular path remains the same.

the diameter of the circular path decreases

An iron rod becomes magnetic when positive ions accumulate at one end and negative ions at the other end. its electrons stop moving and point in the same direction. its atoms are aligned having plus charges on one side and negative charges on the other. the net spins of its electrons are in the same direction. none of these

the net spins of its electrons are in the same direction

The primary of a transformer is the coil connected to the load. the power line. the Internet. none of these

the power line

Compared to radio waves, the velocity of visible light waves in a vacuum is more. the same. less.

the same

Consider light energy that is momentarily absorbed in glass and then re-emitted. Compared to the absorbed light, the frequency of the re-emitted light is considerably more. considerably less. slightly less. slightly more. the same.

the same

There are electrons in the filament of the ac lamp in your bedroom. When you turn on the lamp and it glows, the glowing comes from the same electrons. different electrons; the ones that flow in the circuit to your lamp. the positive charges that flow in the filament.

the same electrons

Two lamps, one with a thick filament and one with a thin filament, are connected in parallel to a battery. The voltage is greatest across the lamp with the thick filament. greatest across the lamp with the thin filament. the same in both lamps.

the same in both lamps

Two lamps, one with a thick filament and one with a thin filament, are connected in series. The current is the same in each lamp. greater in the lamp with the thin filament. greater in the lamp with the thick filament.

the same in each lamp

If a fish looks upward at 45 degrees with respect to the water's surface, it will see only the water's surface. another fish in the pond. the bottom of the pond. the sky and possibly some hills. none of these

the sky and possibly some hills

Red-hot and blue-hot stars appear white to the eye because they are too dim to fire the cones. they are too dim to fire the rods. they are overwhelmed by the blackness of the nighttime sky. eye receptivity peaks in the yellow-green part of the spectrum. the eye has difficulty seeing color at night.

they are too dim to fire the cones

A circuit is powered with a battery. Charge flows through both the battery and the rest of the circuit. from the negative battery terminal to the positive terminal. only after a couple seconds pass. out of the battery and into the circuit. none of these

through both the battery and the rest of the circuit

The main difference between a radio wave and a light wave is its wavelength. speed. frequency. all of these two of these

two of these

Sunburns are produced by visible light. ultraviolet light. infrared light. all of these none of these

ultraviolet light

The natural frequency of the atoms in glass is in the visible part of the spectrum. ultraviolet part of the spectrum. infrared part of the spectrum.

ultraviolet part of the spectrum

The Earth's atmosphere is transparent to most waves in the infrared part of the spectrum. entire electromagnetic spectrum. ultraviolet part of the spectrum. visible part of the spectrum.

visible part of the spectrum