Strongest push at right angles
Turn the rod and watch the force.
Turning a rod
A rod carries a current in a magnetic field. At first the rod makes a small angle with the field. Then it is turned until it is at right angles to the field.
What happens to the force on the rod?
What this lesson covers
The idea
The force on a current-carrying conductor is greatest when the current is at right angles to the magnetic field, and the force is then perpendicular to both.
Turning a rod
A rod carries a current in a magnetic field. At first the rod makes a small angle with the field. Then it is turned until it is at right angles to the field.
What happens to the force on the rod?
- It becomes the greatest
- It becomes the smallest
- It does not change at all
Turn the rod
Move the slider to turn the rod. Watch the green force sign.
Right angles
When the current is at right angles to the field, the rod is pushed the most. In that position the force is also at right angles to both the current and the field. That is why the three directions are drawn at right angles to each other.
The force on a current-carrying conductor is greatest when the current is at right angles to the magnetic field, and the force is then perpendicular to both.
Notes
The force on a current-carrying conductor is greatest when the current is at right angles to the field, and the force is then perpendicular to both.
Check yourself
At which angle between the current and the magnetic field is the force on a current-carrying conductor greatest?
When the current is at right angles to the field, the force on the conductor is…
A rod carrying a current is turned from a small angle with the field to a right angle with the field. The displacement of the rod…
- 45 degrees. The force is greatest when the current is at right angles to the field, so it is smaller at 45 degrees.
- 30 degrees. The force is greatest when the current is at right angles to the field, so it is smaller at 30 degrees.
- 90 degrees, at right angles — correct. Yes!
- perpendicular to both the current and the field — correct. Yes!
- along the direction of the current. The force is perpendicular to both the current and the field.
- along the direction of the field. The force is perpendicular to both the field and the current.
- becomes the smallest. The displacement of the rod is largest when the current is at right angles to the field.
- becomes the largest — correct. Yes!
- stays the same. The displacement depends on the angle: it is largest when the current is at right angles to the field.