Midterm Review

Question 1

Define lenz law

Answer 1

An induced voltage or current opposes the motion that causes it (switches polarity)

Question 2

A Henry is a measure of?

Answer 2

Inductance

Question 3

Define a Henry

Answer 3

A 1 Henry coil induces 1 voltage of current when 1 amp is applied

Question 4

Define inductance

Answer 4

A measure of a circuits ability to induce voltage

Question 5

What causes counter electro motive force (CEMF)

Answer 5

Caused when voltage swaps polarity

Question 6

What affect does inductive reactance have on an AC circuit?

Answer 6

Limit current flow

Question 7

Why doesn’t current rise to max ohms law value when DC is applied to an inductor?

Answer 7

Current gets limited by the electro magnetic field of induced voltage

Question 8

What are the four ac losses

Answer 8

Hysteresis, eddy currents, skin affect, dielectric

Question 9

Is there anytime when electrical degrees match mechanical degrees

Answer 9

Yes, a 2 pole generator

Question 10

What happens when a coil meant to run AC gets connected to DC

Answer 10

Draws more current

Question 11

What devices can be used to prevent voltage spikes in DC

Answer 11

Mov, diodes, resistor

Question 12

What devices can be used to prevent voltage spikes in AC

Answer 12

Resistor, mov

Question 13

What’s the formula to calculate RPM (NS)

Answer 13

Rpm (Ns) = frequency x120/number of poles

Question 14

When a dc source is applied to an inductor a _____ can be inserted in _____ with the inductive load to eliminate voltage spikes

Answer 14

A diode in parallel

Question 15

When an ac source is connected to an inductor an _____ can be inserted in _____ to eliminate voltage spikes

Answer 15

An MOV in parallel

Question 16

What’s the formula for inductive reactance (XL)

Answer 16

XL=2pi x frequency x HENRY’S (Henry’s are measured in L)

Question 17

Formula for EMF

Answer 17

EMF= L x (I/T)

Question 18

Formula for RMS

Answer 18

Rms= epeak x 0.707

Question 19

Formula for E_inst

Answer 19

E_inst= e_max x sin<. (< is angle)

Question 20

Formula for peak 2 peak

Answer 20

Peak x 2

Question 21

Formula for peak

Answer 21

Rms/0.707

Question 22

Average voltage for an AC sine wave

Answer 22

0

Question 23

Formula for time constant

Answer 23

L/R

Question 24

I max formula

Answer 24

Et/r

Question 25

How long till full ohm value (Current)

Answer 25

Time constant x 5

Question 26

Current after time constants formula

Answer 26

I max x (1-E(-1))

Question 27

How to calculate Power factor

Answer 27

Tp/ap

Question 28

How to find our angle in an RL circuit (inductor)

Answer 28

Cos inverse x Power factor

Question 29

Formula for Q

Answer 29

XL/RL

Question 30

Formula for L

Answer 30

XL/ 2pi x FREQUENCY

Question 31

Advantages of AC compared to DC

Answer 31

Can be transformed stepped up or down

Question 32

Advantages of AC compared to DC

Answer 32

Can be transformed stepped up or down