Physics 1320 Chap 25 (Exam 1)

The primary coil of a transformer has five times as many turns as the secondary coil. The output current for the transformer is 1.7 A . Select the correct equations that show that the input current is 0.34 A .

Iinput=Ioutput⋅Nsecondary/Nprimary=1.7A⋅15=0.34A

A transformer for a laptop computer converts a 220-V input to a 10-V output. Select the correct equations that show that the primary coil has twenty two times as many turns as the secondary coil.

Nprimary/Nsecondary=Vinput/Voutput=220V/10V=22

If you drop a bar magnet in a vertical copper pipe it will fall slowly because

it induces a magnetic field in the pipe that resists motion of the magnet.

High-voltage wires in power lines are not high-current wires because the current in them is

not the same as the current that powers the distant load AND proportional to the voltage drop from beginning to end of each line, rather low.

The primary of a transformer is the coil connected to

the input power line.

The discovery of electromagnetic induction is credited to

Joseph Henry in America and Michael Faraday in England

A turbogenerator produces

neither, but transforms energy from one form to another.

When a bar magnet is thrust into a coil of copper wire, the coil tends to

repel the magnet as it enters.

Magnetic field strength inside a current-carrying coil will be greater if the coil encloses a

rod of iron.

Between the consumer and the power plant, most importantly, are

step-down transformers.

Faraday's law underlies the operation of

the changing of traffic lights. an electric guitar. a shake flashlight.

The secondary of a transformer is the coil connected to

the load.

When a magnet is moved to and fro in a wire coil, voltage is induced. If the coil has twice as many loops, the voltage induced is

twice

A transformer actually transforms

voltage

When voltage is induced in a coil of wire, current is

also induced.

A generator armature is more difficult to rotate when supplying electric current due to

an induced magnetic field in the windings that resists change.

The voltage across the input terminals of a transformer is 120 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer delivers is

60 V.

Induced electric and magnetic fields result in

electromagnetic waves.

The output power of an ideal transformer is

equal to the input power.

When a change occurs in the magnetic field in a closed loop of wire

a current is created in the loop of wire. electromagnetic induction occurs. a voltage is induced in the wire.

The current produced by a common generator is

ac

An iron core in a transformer

guides magnetic field lines.

The voltage across the input terminals of a transformer is 120 V. The primary has 25 loops and the secondary has 50 loops. The voltage the transformer delivers is

240 V.

Four amperes of current exist in the primary coil of a transformer. The voltage across the primary coil is 120 V. What is the power output of the secondary coil?

480 W

If you thrust a magnet into a closed loop of wire, the loop will

have a current in it.

A certain transformer doubles input voltage. If the primary coil draws 10 A of current, then the current in the secondary coil is

5 A.

Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on the transformer should be

1 primary to 100 secondary.

A step-up transformer steps up voltage by ten times. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is

100 W.

A step-up transformer steps up voltage by ten times. If voltage input is 120 volts, voltage output is

1200 V.

The metal detectors that people walk through at airports operate via

Faraday's law.

Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage may be produced by

the sudden collapse in the magnetic field.

Each of the transformers shown is powered with 100 W, and all have 100 turns on the primary. The number of turns on each secondary varies as indicated. Rank the currents in the secondaries from greatest to least

ACB

Compared to the primary voltage, the secondary voltage can be

Any of these: higher. lower. the same.

Each of the transformers shown is powered with 100 W, and all have 100 turns on the primary. The number of turns on each secondary varies as indicated. Rank the voltage outputs of the secondaries from greatest to least.

BCA

When voltage is stepped up in a transformer, current is stepped down. But Ohm's law tells us that greater voltage means greater current, not less current. How then can current be lower when voltage is increased?

Current in the secondary is lower when compared to the greater current drawn by the primary AND Ohm's law applies to the circuit connected to the secondary, not to the transformer.

Each of the transformers shown is powered with 100 W, and all have 100 turns on the primary. The number of turns on each secondary varies as indicated. Rank the power outputs in the secondaries from greatest to least.

Equal

Underlying the concept of self-induction is

Faraday's law.

The primary of a transformer connected to 220 V has 100 turns. The secondary has 10 turns. This is a step-down transformer. Select the correct equations that show that the output voltage is 22 V .

Vout=Vin⋅Nsecondary/Nprimary=(220V)⋅10turns/100turns=22V

A transformer has an input of 6 V and an output of 72 V . If the input is changed to 12 V, select the correct equations that show that the output would be 144 V .

Voutput,2=Vinput,2⋅Nsecondary/Nprimary=Vinput,2⋅Voutput,1/Vinput,1=(12V)⋅72V/6V=144V

A friend says that changing electric and magnetic fields underlie the production of light.

agree with your friend

An electric motor is very similar to

an electric generator.

In the field induction credited to Maxwell, wires

are not needed.

The high voltage that is important in a power line is high voltage

between the parallel wires of the line.

The principle difference between a step-up and step-down transformer is

different ratios of turns of wire for each.

Electromagnetism unites

electricity and magnetism.

If the primary of a transformer is connected to a dc power source, the transformer would have a voltage output

only while being connected or disconnected.

The induced electric and magnetic fields of Maxwell are

perpendicular to each other.

The rate at which energy is transferred is

power

The transmission of power from one place to another is evident in

radio broadcast. mobile phones. household electricity.

A transformer transforms voltage while

transferring energy from one coil to another.

An efficient step-up transformer boosts

voltage

The principal advantage of ac power over dc power is that

ac voltage can be transformed via conventional transformers.

Rapid change of a magnetic field induces

an electric field.

A device that transforms mechanical energy into electrical energy is a

generator

Power is transmitted at high voltages because the corresponding current in the wires is

low so that overheating of the wires is minimized.

Electromagnetic induction occurs in a coil when there is a change in

magnetic field intensity in the coil.

Electromagnetic induction is employed in

mobile phones. hybrid automobiles. triggering traffic lights. electric power lines.

A device that transforms electrical energy to mechanical energy is a

motor

Voltage can be induced in a wire by

moving a magnet near the wire. changing the current in a nearby wire. moving the wire near a magnet.

An efficient step-down transformer decreases

neither energy or power.

Thrust a magnet into the opening of a rubber band and it

neither rotates or has a current in it.

A transformer produces

none of the above

Disregarding the effects of friction, a cyclist will coast farther when a lamp powered by a wheel generator is

turned off.