Help with determining the direction of induced currents

[riseofphoenix]

2. Three loops of wire move near a long straight wire carrying a current as in the following figure.

(a) What is the direction of the induced current, if any, in loop A?

a. clockwise
b. counterclockwise
c. No current is induced. (ANSWER)

WHY IS "C" THE ANSWER? I don't understand the concept of determining the direction of an induced current. What does an induced current even mean?? Is it a current caused by something else (such as a long wire in this case)?

(b) What is the direction of the induced current, if any, in loop B?

a. clockwise
b. counterclockwise (ANSWER)
c. No current is induced.

:(:(!

(c) What is the direction of the induced current, if any, in loop C?

a. clockwise (ANSWER)
b. counterclockwise
c. No current is induced.


5. In the figure below what is the direction of the current induced in the resistor at the instant the switch is closed?

a. The current out of the page.
b. No current is present.
c. The current is into the page.

 

[Doc Al]

You need to study up on http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/electric/farlaw.html#c1 and http://hyperphysics.phy-astr.gsu.edu/%E2%80%8Chbase/electric/farlaw.html#c2.

 

[riseofphoenix]

Ohh thanks!

 

[rude man]

2. Three loops of wire move near a long straight wire carrying a current as in the following figure.

(a) What is the direction of the induced current, if any, in loop A?

a. clockwise
b. counterclockwise
c. No current is induced. (ANSWER)

WHY IS "C" THE ANSWER? I don't understand the concept of determining the direction of an induced current. What does an induced current even mean?? Is it a current caused by something else (such as a long wire in this case)?

Faraday: emf = -N d(phi)/dt. Is there a d(phi)/dt for coil A?
phi = B x area of coil.

The others are similarly solved. As Doc Al says, you need Lenz' law to determine direction if a current is induced. Applies to problem 5 also.

b) What is the direction of the induced current, if any, in loop B?[/B]

a. clockwise
b. counterclockwise (ANSWER)
c. No current is induced.

:(:(!

(c) What is the direction of the induced current, if any, in loop C?

a. clockwise (ANSWER)
b. counterclockwise
c. No current is induced.


5. In the figure below what is the direction of the current induced in the resistor at the instant the switch is closed?

a. The current out of the page.
b. No current is present.
c. The current is into the page.