Solenoid Circuit: Understanding Needle Direction with Open and Closed Switch

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SUMMARY

The discussion centers on the behavior of compass needles in relation to a solenoid circuit with a soft iron bar. When the circuit switch is open, both compass needles point north due to the absence of magnetization in the soft iron bar. Upon closing the switch, the soft iron bar becomes magnetized, causing the compass needle on the west side to point either east or west, depending on the current's direction. The compass needle on the north side will point in the opposite direction to the needle on the west side, illustrating the principles of electromagnetism.

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Homework Statement



A soft iron bar in a solenoid is placed in a circuit. There are two compasses, 1 is on the West side of the iron bar and the other is to the North. The circuit switch is open, which way will be compass needles be pointing?
Which way will the compass needles be pointing if the switch is then closed?


Is there a rule to solenoids?
 
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when the switch is open, both needles will point towards north, because soft iron bar is not magnetized.
When the switch is closed, soft iron gets magnetized. Then the the needle placed west side will point either east or west depending on the direction of the current in the circuit.
If you follow the lines of magnetic field, you can see that the needle on the north side will be in the opposite direction compared to the needle on the west side.
 

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