1) A permanent bar magnet with the north pole pointing downward is dropped into

Question

1) A permanent bar magnet with the north pole pointing downward is dropped into a solenoid. (a)Determine the direction of the induced current that woudl be measured in the ammeter shown in the figure below. (b) If the magnet is suddenly oulled upward through the solenoid, what is the direction of the induced current that would be measured in the ammeter?

2) A pair of parallel conducting rails that are 12cm apart lies at the right angles to a uniform magnetic field of 0.8 T directed into the page, as shown in the firgure below. A 15-Ohm resistor is connected across the rails. A conducting bar is moved to the right at 2 m/s across the rails. (a) What is the current in the resistor? (b) What direction is the bar (up or down)? (c) What is the magnetic force on the bar?

Explanation / Answer

1)

a) counter clockwise direction

b) clockwise direction

2) induced emf = B*v*L

i*R = B*v*L

i = B*v*L/R
= 0.8*2*0.12/15
= 0.0128 A

b) up

c) P = i^2*R

F*v = i^2*R

F = i^2*R/v
= 0.0128^2*15/2
= 1.23*10^-3 N

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