Magnetism Lenz's Law (DC and AC motors)

Question 1

What is Lenz’s Law?

Answer 1

“inductors always oppose a change of current”

Question 3

If a magnet is moved toward a coil, magnetic lines of flux begin to cut the conductors of the coil and a current is
then ___ in the coil.

• This ___ current causes magnetic lines of flux to expand outward around the coil.
• As this expanding magnetic field cuts through the conductors of the coil, a voltage is ___ in the coil

Answer 3

induced

Question 4

When a voltage is induced, in a coil and there is a complete circuit, so ____ flows through the coil
* When ____ flows through the coil, a magnetic field is created around the coil.
* This magnetic field develops a polarity ____ that of the moving magnet.
* The magnetic field developed by the induced current acts to ____ the moving magnet and pull it back inside
the coil.

Answer 4

current, opposite, attract

Question 5

Put these letters in the right order to explain Induction and Lenz’s Law?

A) Magnetic field created around coil that opposes moving magnet

B) Magnet move towards coil

C) Magnetic lines of flux cut the conductors of of the coil

D) A complete circuit and expansion of magnetic field cutting through conductor creates current flow.

E) Magnet pulled back inside coil

F) Magnetic lines of flux expand outward around coil

Answer 5

1. B) Magnet move towards coil
2. C) Magnetic lines of flux cut the conductors of of the coil
3. F) Magnetic lines of flux expand outward around coil
4. D) A complete circuit and expansion of magnetic field cutting
   through conductor creates current flow.
5. A) Magnetic field created around coil that opposes moving magnet
6. E) Magnet pulled back inside coil

Question 6

Lenz’s Law

____ reaction for every ____ action

push magnet through

More current more ___ force

Inductors always ___ a charge in ____

Answer 6

opposite

backwards

oppose, current

Question 7

T (____) = L (___, ____) / R (___)

Answer 7

T (Time in secs) = L (Henry, Inductance) / R (resistance)

Question 8

Inductance in AC circuits

XL = 2 pie fL

Inductance proportional to ____

As well as proportional to:

of ___
strength of ____
the ___ of cutting action

(relative motion between inductor and magnetic lines of flux)

Answer 8

Inductance reactance= constant pie * frequency (hertz) * Inductance (H)

Inductance reactance

turns, magnetic field, speed

Question 9

Generation of DC current

Alternator: A generator producing ___

DC generator: has ____

DC generator produces ___ to pulse ___

AC connects ____

Answer 9

AC

communicator

AC, DC

brushes

Question 10

Ripple voltage (not ____)

Fill gapes more concentrated sine wave is ____

Answer 10

wanted, ideal

Question 11

Rotate magnet in stationary wire (___)

Or rotate wire in stationary magnet field (___ generator)

Answer 11

AC, DC

Question 12

Prime movers (turbines and engines produce ____)

two ____ Strip rings and brushes (___)
Computator (___)

____ - variation of every change in voltage per one ____

parallel ___
____ (flux lines at max cut at full speed) - E = Blv

Answer 12

energy
metal bands, AC, DC

Sine wave, revolution

zero, perpendicular

Question 13

Induction

____ magnet
____ magnet

Electromagnetic Induction
-transfer ____ from one place to anther

____ - charged store energy

Still = ____
moving = ____

Answer 13

charge, create

energy

Electrostatics

nothing, EMF produced

Question 14

Three Ringer left hand rule:

Thumb =

Forefinger =

Center finger =

Answer 14

Thumb = movement of conductor

Forefinger = direction of flux (north to south)

Center finger = ( direction of current)

Question 14

E = BLV is what law?

E=

B =

L =

V =

Answer 14

Faraday’s Law

E= Generated voltage

B = Flux density in Teslas

L = the active length of the conductor in metres

V = velocity or speed which the flux lines are cut

Question 14

less turns = ____

Answer 14

voltage

Question 15

___voltage = ____ turns

Answer 15

less

Question 16

stationary = ___ volts

Answer 16

zero

Question 17

Eddy currents What is it?

Copper: does not conduct electricity, True or False?

Moving copper or magnet - creates ____

Answer 17

opposing magnetic field force (voltage?) to halt conductor by circular currents

False

electric current

Question 18

Inductor: coil and two lines

Air-core - only coils

True or False?

Answer 18

True

Question 19

Rotor - connects to ___

stator - ____ provide magnetic field (usually wound electromagnet)

Answer 19

armature, field poles

Question 20

Self excited - series external load (low turns)

Separately excited - no ____ (electromagnet) - attracted to battery or rectifier

Answer 20

permanent magnet

Question 21

Shunt - ____

what is it?

Compound - ___ resistance series, ___ resistance parallel

Answer 21

Field pole coil

small, high

Question 22

Vertical:

Flat:

Degrees - 90, 180, 270, 360

Which degrees is vertical and flat

Answer 22

Vertical: 360 and 180

Flat: 270 and 90

Question 23

Magnetic Induction - amount of voltage induced in a conductor determined by?

-

-

-

Answer 23

• The number of turns of the wire
• The strength of the magnetic field (flux density)
• The speed of the cutting action