Question Video: Determining the Direction of Current in a Conducting Loop Moving in a Uniform Magnetic Field | Nagwa Question Video: Determining the Direction of Current in a Conducting Loop Moving in a Uniform Magnetic Field | Nagwa

# Question Video: Determining the Direction of Current in a Conducting Loop Moving in a Uniform Magnetic Field Physics • Third Year of Secondary School

A conducting loop is moved so that half of its area is within a uniform magnetic field, directed out of the plane of the diagram shown along the axis of the loop; then the loop moves from being partially within the magnetic field to being completely within the magnetic field. Is the current through the loop clockwise or counterclockwise?

02:05

### Video Transcript

A conducting loop is moved so that half of its area is within a uniform magnetic field, directed out of the plane of the diagram shown along the axis of the loop. Then, the loop moves from being partially within the magnetic field to being completely within the magnetic field. Is the current through the loop clockwise or counterclockwise?

The question asks what the direction is of the current induced in the conductive loop due to the motion of the loop into a uniform magnetic field. Initially, only half of the loop is located within the magnetic field, but recall that the loop is moving. The motion of the loop in the magnetic field results in a magnetic force acting on free electrons in the loop. The forces on the free electrons act to produce a net motion of the free electrons around the loop.

The answer to the question depends on which direction around the loop the free electrons move in, as the direction of the current in the loop is opposite to the direction of the net flow of the free electrons. When charged particles move in a magnetic field, the direction of the induced current can be determined using Fleming’s right-hand rule. Let us use this rule with the loop.

The direction of the magnetic field is out of the plane of the screen. We see then that when the direction of the motion of the loop is toward the right, the direction of the induced current is toward the bottom edge of the loop. Recall that the direction of motion of free electrons is opposite to the direction of current. Free electrons are therefore pushed toward the top edge of the loop.

When free electrons move toward the top edge of the loop, the concentration of negative charge is greater at the top edge of the loop and less at the bottom edge of the loop. The greater concentration of negative charge at the top edge of the loop repels free electrons at the top edge of the loop, which therefore move toward the left. The lesser concentration of negative charge at the bottom edge of the loop attracts free electrons at the bottom edge of the loop, which therefore move toward the right.

We see then that the net flow of free electrons is directed counterclockwise. The direction of the current in the loop is opposite to the direction of the net flow of free electrons. So the current induced in the loop is clockwise.

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