PHYS1001 Chapter: 25 Electromagnetic Induction
Fred swings a sheet of copper in pendulum fashion between the poles of a strong magnet. The sheet slows in entering the magnetic field because it..?
Induces swirling currents in the copper and accompanying magnetic fields that resist motion
If you drop a bar magnet in a vertical copper pipe it will fall slowly because..?
It induces a magnetic field in the pie that resists motion of the magnet
The discovery of electromagnetic induction is credited to..?
Joseph Henry in America and Michael Faraday in England
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
The primary pf a transformer..?
May or may not have an iron core
A device that transforms electrical energy to mechanical energy is a..?
Motor
An efficient step-down transformer decreases..?
Neither of these
Thrust a magnet into the opening of a rubber band and it..?
Neither of these
A transformer produces..?
None of the above
The major advantage of MHD generators over conventional generators is that MHD generators..?
None of the above
The induced electric and magnetic fields of Maxwell are..?
Perpendicular to each other
The rate at which energy is transferred is called..?
Power
The strength of the induced electric or magnetic field depends on..?
Rate of change of the induced field
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 transformer
A turbogenerator produces..?
neither, but transforms energy from one form to another
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
A transformer transforms voltage while..?
transferring energy from one coil to another
To reduce the danger of self-induction..?
turn off the switch to the circuit
When voltage is induced in a coil of wire, current is..?
also induced
Rapid change of magnetic field induces..?
an electric field
An electric motor is very similar to..?
an electric generator
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
The output of power on an ideal transformer is..?
equal to the input power
The current produced by a common generator is..?
ac
An iron core in a transformer..?
guides magnetic field lines
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
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
The principle advantage of ac power over dc power is that..?
ac voltage can be transformer via conventional transformers
a force field is induced in any region of space in which..?
-An electric field changes with time -A magnetic field changes with time
Faraday's law was extended by Maxwell toward..?
-Changes in electric fields -Changes in magnetic fields
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. -Ohm's law applies to the circuit connected to the secondary, not to the transformer.
The transmission of power from one place to another is evident in..?
-Household electricity -Radio broadcast -Mobile phones
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 -Proportional to the voltage drop from the beginning to the end of each line, rather low
Voltage can be induced in a wire by..?
-moving the wire near a magnet -moving a magnet near the wire -changing the current in a nearby wire
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 100W of power go into the primary coil, the power coming from the secondary coil is..?
100W
A step-up transformer steps up voltage by ten times. If voltage input is 120 volts, voltage output is..?
1200V
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
When a change occurs in the magnetic field in a closed loop of wire..?
A voltage is induced in the wire, a current is created in the loop of wire, electromagnetic induction occurs
A friend says that changing electric and magnetic fields underlie the production of light..?
Agree with your friend
The voltage induced in self-inductions is..?
Always in a direction opposing the changing voltage that produced it, Likely higher than the changing voltage that causes it
Faraday's law underlies the operation of..?
An electric guitar, a shake flashlight, and the changing of traffic lights
A generator armature is more difficult to rotate when supplying electric current due to..?
An induced magnetic field in the windings that resists change
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 amount of current produced by electromagnetic induction depends on the..?
Both the amount of induced voltage and resistance of the circuit to which it is connected
The principle difference between a step-up and step-down transformers is..?
Different ratios of turns of wire for each
Electromagnetic induction is employed in..?
Electric power lines, triggering traffic lights, hybrid automobiles, mobile phones
Induced electric and magnetic fields result in..?
Electromagnetic waves
The metel detectors that people walk through at airports operate via..?
Faraday's Law
Underlying the concept of self-induction is..?
Faraday's law
A device that transforms mechanical energy into electrical energy is a..?
Generator
A principle difference between an MHD generator and a conventional generator is that the MHD generator..?
Has no moving parts and operates more efficiently at high temperatures
If you thrust a magnet into a closed loop of wire, the loop will..?
Have a current in it
Compared to the primary voltage, the secondary voltage can be..?
Higher, lower, the same
The frequency of induced voltage in a wire coil depends on..?
How frequently a magnet dips in and out of the coil
If the voltage produced by a generator alternates, it does so because..?
The changing magnetic field that produces it alternates
The primary of a transformer is the coil connected to..?
The input power line
The secondary of a transformer is the coil connected to..?
The load
Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage is produced by..?
The sudden collapse in the magnetic field
The spacing between the parallel power lines is affected by..?
The wing span of birds in the vicinity
Disregarding the effects of friction, a cyclist will coast farther when a lamp powered by a wheel generator is..?
Turned off
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
An efficient step-up transformer boosts..?
Voltage
Transformers use ac to satisfy the required..?
change in magnetic field for operation
Electromagnetism unites..?
electricity and magnetism