Chapter 21 EMF induced & AC Circuits

Question 0

What is the difference between magnetic flux and magnetic field? Discuss in detail.

Answer 0

Flux = BA , two current carrying wires with the area into account. Magnetic field is only the field lines.

Question 1

What would be the advantage, in Faraday’s experiments, of using coils with many turns?

Answer 1

The more turns in a coil the greater amount of current generated in the opposite direction so that the magnet drops slower.
Emf oc # of turns
More evidence of induced current
Emf = N • change in flux / change in T

Question 2

Suppose you are holding a circular piece of wire and suddenly thrust a magnet, South Pole first, toward the center of the circle. Is a current induced in the wire? Is the current induced when the magnet is held steady within the loop? Is the current induced when you withdraw the magnet? In each case, if your answer is yes, specify the direction.

Answer 2

1. Yes, increase dots, increase x 
Clockwise 
2. No, no movement
3. Yes, decrease dots, increase dots 
Counterclockwise

Question 3

In what direction with the current flow in figure 21–9 if the right moves to the left, which decreases the area of the loop to the left?

Answer 3

Increase dots, increase x, clockwise

Question 4

Two loops of wire are moving in the vicinity of a very long straight wire carrying a steady current as shown in figure 21–42. Find the direction of the induced current and each loop.

Answer 4

^ I 
(A). 〇     |     (B). 〇
       ^                —> V
        | V 
a. No induced current, moving in same direction
b. Decrease x, increase x, clockwise