Today4/10 Current Loops

“Phantom” magnets Force/torque on loops in a B-field

HW: 4/10 “Force on Loops” Due Monday, 4/14

Current loops

B Fields - Current Loop

SN

Current loops are magnets!!! Behave like magnets!!!

B Fields - Magnet

Current loops

N S

B Fields - Current Loop

Phantom Bar Magnet

Magnetic Torque, LoopsWhat happens to loop?

Turn the loop into a magnet. Magnets line up with the field. (A compass needle is a magnet!)

Loop is a magnet (needle) centered in the loop with the N pole facing away from you.S

The loop (magnet) will rotate so it lines up with the field. (S up and out of the page)

Magnetic Torque, LoopsWhat happens to loop?

S

N The loop (magnet) will rotate so it lines up with the field. (S up and out of the page)

Turn the loop into a magnet. Magnets line up with the field. (A compass needle is a magnet!)

Loop is a magnet (needle) centered in the loop with the N pole facing away from you.

This is a torque on the loop.

N S

N S

N S

N S

A bar magnet and current loop (powered by a battery) are shown in various orientations below. In each case the magnet if held in place and the current loop is released and allowed to rotate only about the axis shown. Determine if the loop will rotate. If so, find the direction of rotation and how far it rotates. If the loop is in unstable equilibrium, say so. (RHR #3)

Torque clockwise from above, can’t turnNorth out

Unstable equilibrium small tap will cause a 180° flip either direction. North right

Clockwise (viewed from above) 90°North out

Clockwise (viewed from above) 90°North in

Magnetic Force, LoopsWhat happens to loop?

Turn the loop into a magnet. Like poles repel.

Loop is a magnet (needle) centered in the loop with the N pole facing away from you.SN

Unlike poles attract so the loop is attracted, force on loop is to the left.

real magnet

Magnetic Force, LoopsWhat happens to loop?

Turn the loop into a magnet. Like poles repel.

Loop is a magnet with the N pole facing left

Like poles repel so the loop is repelled, force on loop is to the right.

S N SN

real magnet