Induction Experiments and E.m.f. Size
Induction Experiments and E.m.f. Size
- The meter reading is the measured result. Change one factor at a time to find what controls the induced e.m.f.
Move a straight wire through a field
Swipe left or right to see the whole diagram →
- The wire is connected to a centre-zero meter and placed between magnetic poles. The meter shows the size and direction of the induced current.
- Move the wire across the field: the meter deflects. Stop the wire: the reading becomes zero.
- Reverse the motion or the magnetic field: the deflection reverses.
- The wire must cut across the field. Motion parallel to the field gives no induced e.m.f.
Change one factor at a time
For a straight wire, the peak induced e.m.f. becomes larger when one of the following increases while the others remain fixed:
- magnetic flux density;
- wire length inside the field;
- speed perpendicular to the field.
For a coil, a larger field, larger area, more turns or a faster change can produce a larger e.m.f. To test speed, use the same magnet, coil and path, and change only the speed. The dependent quantity is the peak meter reading.
Hand motion is not perfectly repeatable. A data logger and a guided moving holder reduce uncertainty in the peak reading and speed.
Common mistake
A student uses a stronger magnet but moves it more slowly. The peak e.m.f. is unchanged. Can the student conclude that magnet strength has no effect? Explain.
Show worked answer
No. Two relevant quantities changed. The stronger field tends to increase the e.m.f., while the lower speed tends to decrease it. Speed must be controlled to test field strength alone.