Tbr ch 8 #8

[yjj8817]

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I don't understand how the bar can be suspended when there is only magnetic field created by the current.

I thought current can only create magnetic field. But the passage says there is magnetic force even though there is not external magnetic field.

The answer is A btw.

Can someone clarify?

 

[yjj8817]

 

[erythrocyte666]

View attachment 187884View attachment 187885

I don't understand how the bar can be suspended when there is only magnetic field created by the current.

I thought current can only create magnetic field. But the passage says there is magnetic force even though there is not external magnetic field.

The answer is A btw.

Can someone clarify?

If you have a magnetic field (which you correctly say there is) and moving charge (the current through closed loop aXYf) while the battery is on, then by definition you have a magnetic force (think F = iLB, F = qvB, etc.). As the passage says, this magnetic force opposes gravitational force, thereby keeping the bar suspended.

 

[yjj8817]

If you have a magnetic field (which you correctly say there is) and moving charge (the current through closed loop aXYf) while the battery is on, then by definition you have a magnetic force (think F = iLB, F = qvB, etc.). As the passage says, this magnetic force opposes gravitational force, thereby keeping the bar suspended.

I thought the magnetic field has to be external, not from the charges to create force. It says that there is no external magnetic field.

 

[erythrocyte666]

I thought the magnetic field has to be external, not from the charges to create force. It says that there is no external magnetic field.

Magnetic field can be induced by the current in the closed loop

 

[yjj8817]

Magnetic field can be induced by the current in the closed loop

Right, but to create force the magnetic field has to be external, not from the charges themselves.

 

[erythrocyte666]

Right, but to create force the magnetic field has to be external, not from the charges themselves.

The moving current in the closed loop induces an upward B field within the loop. This magnetic field provides the upward magnetic force.

 

[yjj8817]

Anyone else?

 

[yjj8817]

The moving current in the closed loop induces an upward B field within the loop. This magnetic field provides the upward magnetic force.

It clearly says in my tpr physics book that magnetic field exerts a force only on other moving charges

 

[erythrocyte666]

Think of the current through segment aX (or Yf) exerting an upward magnetic field on bar XY - that's your "external magnetic field".

Current moves from X to Y, there is a perpendicular upward magnetic field (caused by the other segments) - so use the right hand rule to confirm the upward magnetic force.

The "external magnetic field" created by the current through segments aX and Yf are exerting "a force on the moving charges" through bar XY