The figure below shows a conducting bar of length 40.0 cm that can move without

Question

The figure below shows a conducting bar of length 40.0 cm that can move without friction on a pair of conducting rails. The rails are joined at the left by a battery of emf 6.00 V, and a switch that is initially open. The bar, which is initially at rest, has a resistance 8.00 ?, and we will assume the resistance of all other parts of the circuit is negligible. The whole apparatus is in a uniform magnetic field, directed into the page, of magnitude 0.500 T. Both the rails and the magnetic field extend far to the left and right.

(a) What is the current in the circuit immediately after the switch is closed (Take counterclockwise to be the positive direction. Indicate the direction with the sign of your answer.)

(b) What is the net force on the bar immediately after the switch is closed (Take the positive direction to be to the right. Indicate the direction with the sign of your answer.)

(c) What is the current in the circuit a long time after the switch is closed (By "a long time," we mean that enough time has passed for the bar to reach a terminal [constant] velocity. Take counterclockwise to be the positive direction. Indicate the direction with the sign of your answer.)

The figure below shows a conducting bar of length 40.0 cm that can move without friction on a pair of conducting rails. The rails are joined at the left by a battery of emf 6.00 V, and a switch that is initially open. The bar, which is initially at rest, has a resistance 8.00 ?, and we will assume the resistance of all other parts of the circuit is negligible. The whole apparatus is in a uniform magnetic field, directed into the page, of magnitude 0.500 T. Both the rails and the magnetic field extend far to the left and right. (a) What is the current in the circuit immediately after the switch is closed (Take counterclockwise to be the positive direction. Indicate the direction with the sign of your answer.) (b) What is the net force on the bar immediately after the switch is closed (Take the positive direction to be to the right. Indicate the direction with the sign of your answer.) (c) What is the current in the circuit a long time after the switch is closed (By a long time, we mean that enough time has passed for the bar to reach a terminal [constant] velocity. Take counterclockwise to be the positive direction. Indicate the direction with the sign of your answer.)

Explanation / Answer

A.

I = emf/R

= 0.75 A   [ANSWER, PART A]

***************

F = BIL

= 0.15 N   [POSITIVE BY RIGHT HAND RULE, ANSWER, PART B]

**************

At terminal velocity

emf = BLv

--> v = emf / BL

thus,

v = 30 m/s   [ANSWER, PART C]

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