78 terms

Honors Physics Chapter 20

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Michael Faraday
who first demonstrated the principle of electromagnetic induction
Electromagnetic induction
producing current in a wire by placing it in a changing magnetic field
wire&wire
Either the ____ can move in the magnetic field or the field can move around the ____ - one or the other must move to induce current.
-rotate a wire
-drag a wire through magnetic field
-move a magnetic field across a wire
three ways to induce current
emf
Separation of charges by magnetic force will induce ____in the wire
electrons
The magnetic field force pushes the___ through the wire
3rd
Use the ___ right hand rule to figure out the direction of current flow in the wire
-speed of wire or magnetic field motion
-length of wire in the field
-strength of magnetic field
Magnitude of emf depends on (3):
perpendicular
Induced current is greatest if the wire and magnetic field are_____ to each other
parallel
if the angle is zero the wire is____ to the magnetic field
perpendicular
Only the portion of the magnetic field____ to the wire will induce current in it
size & rotating
Changing the ___ of the loops of wire or _____ the loop in the magnetic field will change the amount of induced current
magnetic field
The current induced in the wire by moving through a magnetic field will generate its own _______
opposite
As the magnetic field approaches the wire, the wire's magnetic field is in the____ direction of the increasing magnetic field
bar magnet
The induced magnetic field is similar to a _____- and creates a force that repels the original magnetic field
same
As the coil moves out of the magnetic field the induced field is in the_____ direction as the original and they attract each other
lens law
"The magnetic field of an induced current is in a direction to produce a field that oppose the change causing it"
CHANGE
The induced field does not oppose applied field, but the____ in the applied field
induced field
If the applied field changes, the _____ helps to keep it constant
Faraday's Law of Induction
Predicts the magnitude of induced emf
Lenz's law
tells the direction of the induced emf
Equation for single loop
emf = -∆ϕM/∆t
emf from one loop
When you have multiple loops, you multiple the number of loops (N) by the ____
equation for multiple loops
N∆ϕM/∆t
volt (V)
emf unit is the
orientation
Current can also be generated in a magnetic field by changing the_____ of the loop in the magnetic field
mechanical energy
Most power plants use a source of _____ to turn a turbine in a magnetic field to generate current.
emf
A generator produces changing____, because of its constant rotating
0 emf
when the armature is perpendicular to the magnetic field in a generator, you get____
maximum emf
when the armature is parallel to the magnetic field in a generator, you get ____
AC current
As the loop rotates from one arm being up to the other being up, the current flow will change direction - producing ____
emf for generator (maximum)
emf = NAβω
ω
is the angular speed of rotation of the loop (2πf)
frequency
The____ of rotation of the loop in a generator will determine how often the current changes direction -> f = 60Hz in US
AC can be converted to DC
add rings (slip rings) and brushes to the end of the loops, the moving rings counter the changing current and create direct current for a circuit
motor
convert electrical energy to mechanical energy
permanent magnet
Current is supplied to loops and that magnetic field repels ______ and causes the loops to rotate
back emf
The motor's magnetic field generates its own emf called ___
Back emf
____ increases as the magnitude of the magnetic field changes at a higher rate
potential difference
The _____ supplied to the motor equals the applied emf minus the back emf, this also reduces current
reduce
As a motor turns more quickly, the net emf and net current in the coil___
Mutual inductance
____ is the ability of one circuit to induce emf in a nearby circuit in the presence of a changing magnetic field
Mutual inductance
emf = - M(∆I/∆t)
M
__ depends on the shape of the coils and how they are orientated to each other
M
is the mutual inductance of the two-coil system
number
Changing the____ of coils in the secondary coil can change the induced emf in the secondary coil - used in making transformers
emf & current
Because AC current changes direction, the____ and____ in an AC circuit is not constant
emf & current
Effective ___ and effective ____ are the average values in the AC circuit - called Irms
Ohm's Law
You can use ____ to find resistance
transformers
A device that increases or decreases the emf of alternating current
first coil called primary
current in this coil magnetizes the iron core
Second coil called secondary
current runs through the 2nd coil because it is wrapped around magnetized iron
Real transformers
_____ are only 90-99% efficient - power is lost due to small currents induced by changing magnetic field and resistance in the wires
transformer equation
∆V2/∆V1 = N2/N1
Step-up transformer
increases the emf, N2 is greater than N1
Step-down transformer
decreases the emf, N2is less than N1
decrease
The increase in emf means a____ in current
increase
An decrease in emf means an____ in current
230 000V
In the US, power companies step-up emf to about ____
12V
Car batteries provide a constant DC emf of ___
The Ignition coil
____ in the engine is a transformer that increases this emf to a great enough value to cause a spark between the gaps of a spark plug
electromagnetic waves
Oscillating electric and magnetic fields create
James Clerk Maxwell
____created a set of equations that explain the relationship between electric and magnetic fields
electromagnetic in nature
Maxwell predicted that light was ___-
Heinrich Hertz
___performed experiments that generated and detected EM waves and confirmed Maxwell's predictions.
transverse waves
electromagnetic waves are ___
right
Oscillating Electric and Magnetic waves - at___ angles to each other
single force
Electric and magnetic forces are aspects of a ____ - called electromagnetic force
inverse square law
Electromagnetic force obeys the ____ - as the two objects move further apart the force between them weakens
accelerating charges
All EM waves are produced by ____ - a charge moves up/down through the wave at a certain frequency
charged particular
motion of _____ through a wave makes it move
energy
Electromagnetic waves transfer____ - stored in the oscillations of the electric and magnetic fields
Electromagnetic Radiation
Energy transported by EM waves is called ____
particles
Some high energy EM waves will behave like____
wave-particle duality of light
Notion that EM waves behave like particles is called the____
photon
A particle of light is called a____ - carries energy, but has no mass
waves
Low-energy photons behave more like ___
particles
High-energy photons behave more like____