7. Lines of the magnetic field produced by a long straight wire carrying a curre

Question

7. Lines of the magnetic field produced by a long straight wire carrying a current are: A) in the direction of the current B) opposite to the direction of the current C) leave the wire radially D) circles concentric with the wire E) lines similar to those produced by a bar magnet 8. Magnetic ield lines inside the solenoid shown are: A) clockwise circles as one looks down the axis from the top of the page B) counterclockwise circles as one looks down the axis from the top of the page toward the top of the page D) toward the bottom of the page E) in no direction since B-0 9. The emf developed in a coil X due to the current in a neighboring coil Y is proportional to the: A) magnetic field in X B) rate of change of magnetic field in X C) resistance of X D) thickness of the wire in X E) current in Y 10. The stored energy in an inductor: A) depends, in sign, upon the direction of the current B) depends on the rate of change of current C) is proportional to the square of the inductance D) has units J/H E) is none of the above

Explanation / Answer

7.

D) circles that concentric with the wire

Using right hand screw rule

it's one of the "right hand rules." Take a length of wire, straight, curly, circular, whatever. Now plug it into your circuit and make sure you know which way the current is flowing

So if your thumb is pointing away, the field is curving to your right. If you're tweaked around so that your right thumb s pointed back, it's curling to your left -- but the field itself is still curing in the same direction relative to the current.

8.

Magnitic field inside the solinoid is uniform

so the line of force are straight and parallel to eachother.

In uniform mag.field the line of forces are parallel to eachother

Note : tangent drawn to the line of force givesdirection of magnetic field.

In the above fig. current is enters . So, according to Flemingleft hand rule,

force is

D) towards the top of the page.

mag.field lines inside the solinoid is towards the topof the page

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