Unit 3B Physics: Electromagnetic Induction

3 ways to induce a current in a circuit:

1. move the circuit into or out of the magnetic field 2. rotate the circuit in the magnetic field 3. change the intensity or direction of the magnetic field.

The RMS current is a little more than _______ as large as the maximum current

2/3

the frequency of the alternating current in the united States in _________Hz. the frequency of the alternating current in the UK, Europe, and Asia is ________ Hz

60 Hz 50Hz

the transformer equation assumes that no power is lost between the transformer's primary and secondary coils, however real transformers typically have an efficiency between ____________% to __________%

90% to 99%

Describe Faraday's model of electromagnetic induction:

Faraday developed his model with a switch connected to a battery instead of a magnet to produce a magnetic field. He called the coil, the primary coil and the circuit the primary circuit. A second coil was wrapped around the iron ring and was known as the secondary coil. An emf is induced in this coil when the field of the primary coil is changed. When the switch in the primary coil is closed, the galvanometer deflects in the opposite direction and then returns to zero.

the basic principle of electromagnetic induction was introduced by:

Michael Faraday

the conducting loop in an ac generator must be free to rotate at all times. It must also be a part of the electrical circuit at all times. How is this accomplished?

This is accomplished because the ends of the loop are connected to conducting rings called slip rings which rotate with the loop.

an ac circuit consists of:

a combination of circuit elements and an ac generator, or power supply which provides the alternating current.

transformers:

a device that increases or decreases the emf of alternating current.

generator:

a machine which converts mechanical energy to electrical energy.

commutator:

a single split ring which reverses the current in the loop.

effective current and effective emf are measured in:

ac circuits.

alternating current:

an electric current that changes direction at regular intervals.

Faraday's Law:

average induced emf= -number of loops in the circuit x the time rate of change in the magnetic flux.

slip rings:

conducting rings that rotate with the loop.

alternating current changes direction at a:

constant frequency

a generator produces:

continuously changing emf

resistance influences ____________ in an ac circuit

current

a motor is almost identical in construction to a:

dc generator

because the strength of the magnetic field in the iron core and the cross sectional area of the core are the same for both the primary and secondary windings, the measured ac potential difference across the two windings differs based on the:

different number of turns of each wire.

alternating current can be converted to ___________ current

direct current

by varying the arrangement of an ac generator slightly, ac current can be converted to:

direct current

the rate at which electrical energy is converted to internal energy in the resistor has the same form as:

direct current

the energies are different in effective current because :

during a cycle the alternating current is at its maximum value only for an instant.

how does a commutator affect the conversion from ac current to dc current?

each half of the commutator comes into contact with the brush. The reversed current in the loop changes direction again so that the output current has the same direction as it originally had, although it still changes from aa maximum value to zero.

real transformers are not perfectly:

efficient

the separation of charges by the magnetic force induces an _________

emf

Suppose a bar magnetic is pushed into a coil of wire. As the magnet moves into the coil, the strength of the magnetic field within the coil increases and the current is induced within the circuit. This induced current produces its own magnetic field whose direction can be found using the right hand rule.

explanation

changing the size of the circuit loop or rotating the loop changes the number of _____________ ___________ passing through the loop.

field lines

the back emf increases in magnitude as the magnetic field changes at a higher rate. the faster the coil rotates, the ___________ the back emf becomes.

greater

one way to _______________ an emf in a closed loop is to move all or part of a loop into or out of a constant magnetic field.

induce

changing the size of the loop or the strength of the magnetic field will:

induce an emf in the circuit.

the angle between a magnetic field and a circuit affects:

induction

motors:

machines that convert electrical energy to mechanical energy

Michael Faraday's electrical apparatus consisted of a coil connected to a switch and a battery instead of a _____________ to produce a magnetic field.

magnet

The magnetic force is perpendicular to the _________________ and ________________

magnetic field and motion of charges.

change in the number of ________________ ________________ ______________ induces a current.

magnetic field lines

one way to predict whether a current will be induced in a given situation is to consider how many ________________ _____________ ____________ cut through the loop.

magnetic field lines

charged particles moving with a velocity at an angle to the magnetic field will experience a:

magnetic force

the rate at which the coil in an ac generator rotates determines the:

maximum generated emf.

the induced emf is smallest (zero) when the plane of the loop is _________________ to the magnetic field.

parallel

the induced emf is largest when the plane of the loop is ______________ to the magnetic field.

perpendicular

the separation of positive and negative moving charges by the magnetic force creates a __________________ _____________________ between the ends of a conductor.

potential difference

why is power lost in a transformer?

power is lost because of the small current induced by changing the magnetic fields in the transformers iron core and because of the resistance between the wires in the windings.

the coil in Faraday's model was known as the ______________ and the circuit was called the _____________

primary coil primary circuit

a current will be induced when there is _____________ _____________ between the circuit and the magnet.

relative motion

_______________ resist the motion of charges regardless of whether they move in a continuous direction or shift direction periodically.

resistors

_________________ can be used in alternating or direct current applications.

resistors

the change with time of the induced emf in a rotating loop is depicted by the:

sine wave

brushes:

stationary graphite strips which make continuous contact with the slip rings in a generator.

mutual inductance:

the ability of one circuit to induce an emf in a nearby circuit.

back emf:

the emf induced within a motors coil that tends to reduce the current in the coil of the motor.

Lenz's Law:

the magnetic field of the induced current is in a direction that produces a field which opposes the change causing it.

Electromagnetic induction:

the process of creating a current in a circuit loop by changing the magnetic flux in the loop alt. definition: the process of creating a current in a loop by changing the magnetic field that passes through the circuit.

the rms emf across a resistor equals:

the rms current multiplied by the resistance

the electrical energy converted to internal energy is proportional to:

the square of the instantaneous current

RMS current:

the value of the alternating current that gives the same heating effect that the corresponding value of direct current does.

the induced emf is smaller when the plane of the loop is _________________ to the magnetic field.

tilted

in its simplest form what does a transformer consist of?

two coils of wire wound around a soft iron core.

for a rotating loop, the induced emf is ______________ when the loop is perpendicular to the magnetic field. It is at a maximum when the loop is parallel to the field.

zero maximum