AC Theory Level 1 lesson 1

At what percentage is the current after five time constants?

100%

Counter Electromotive Force is sometimes called back EMF, and CEMF is ? out-of-phase with the applied voltage.

180 degrees 1Q10

How many time constants does it take for current to reach its maximum value in an inductive circuit?

5 1Q15

At what percentage is the current after one time constant when the circuit is first energized?

63.2% 1Q16

At what percentage is the current after two time constants?

86.4%

At what percentage is the current after three time constants?

94.9%

At what percentage is the current after four time constants?

98.1%

Whenever an electric current flows through a conductor, a magnetic field is formed ? the conductor.

Around 1Q7

As current flow decreases, the magnetic field surrounding the conductor will ? .

Decreases 1Q5

When a conductor moves through a stationary magnetic field an EMF is induced, but when the magnetic field moves and the conductor remains stationary no EMF is induced.

False 1Q6

As the current passing through a coil increases, the magnetic field around the coil will ? .

Increase 1Q5

? Law states that an induced voltage or current opposes the motion that causes the induced voltage or current.

Lenz's 1Q8

Which items listed below are factors that work in combination to affect the inductance produced by an inductor. I. Cross sectional area of the core II. Number of turns of wire III. Permeability of the core material IV. Spacing between the turns V. All the Above

V. 1Q12

When current flows in a conductor, a magnetic field is produced. As free electrons move in one direction, their individual magnetic fields ? .

add together 1Q3

In high frequency applications, ? inductors are used because of eddy current loss and hysteresis loss in the core material.

air core Note: Remember from earlier chapters, that some core materials such as soft iron are affected when used at higher frequencies. The eddy current losses and hysteresis loss make soft iron a poor choice for use in high frequency applications. 1Q19

When no current flows in a conductor, free electrons move ? , and their magnetic fields cancel.

at random 1Q2

The direction of induced ? flow through a conductor is determined by the direction of the magnetic field surrounding the conductor and the direction the conductor is traveling through the magnetic field.

current 1Q1

Inductors always oppose a change of ? .

current 1Q9

The rate of current change in an inductive circuit can be described as a(n) ? curve.

exponential 1Q14

The unit of inductance is the ? , and inductance is represented by the letter ? .

henry / L 1Q17

Whenever current flows through a conductor, a ? is created around the conductor.

magnetic field 1Q1

If a change of one ampere in one second causes one volt to be induced, you have ? of inductance.

one henry 1Q18

The important factors needed for generation of an induced voltage are a conductor, a magnetic field, and ? .

relative motion 1Q4

CEMF ? the applied EMF when current is increasing and ? the applied EMF when current is decreasing.

subtracts from / adds to 1Q11

Whenever a conductor cuts through magnetic lines of flux, a ? is induced into the conductor.

voltage 1Q1