Inductance
General Demonstration
An inductor is used to create a large emf across a switch and arcing is observed.
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- Various coils
- Coil with a large inductance
- Car battery (12 V)
- Inductance meter
- Connecting wires
- Knife switch
An inductance meter is used to measure the inductance of various coils. A circuit is then set up in which a coil with a large inductance is connected through a high capacity knife switch to a 12 V car battery. When the switch is closed for a time and then quickly opened, an arc is observed across the contacts of the switch.
Dependence on Permeability (mu)
Different materials are placed in the core of an inductor and the inductance is measured.
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- Air core coil
- Inductnce meter
- Various rods (wood, glass, iron)
An inductance meter is connected to an air core coil. The inductance is first measured for the empty coil and then it is measured as various rods (wood, glass, and iron) are inserted into the core, one at a time. Magnetic effects beyond three figure accuracy are neglected in this demonstration.
Dependence on Turns (N)
The inductance of a coil is measured as the number of turns is doubled while other variables remain constant.
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- Wooden rod
- Spool of insulated copper wire
- Inductance meter
A coil of 100 turns is first wound onto a wooden rod and the inductance is measured. Another 100 turns is then added to this coil, for a total of 200 turns, while keeping the geometry essentially the same. The inductance is again measured and compared to the first measurement.
Dependence on Length (l)
The inductance of a coil is measured as the length is changed while other variables remain constant.
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- Coil wound on a wooden rod
- Inductance meter
A coil of 50 turns is loosely wound on a wooden rod. The length of the coil is noted and the inductance is measured. As the coil is then compressed to a shorter length, the change in inductance is observed.
Dependence on Cross Sectional Area (A)
The inductance of two coils of different cross sectional areas is measured and compared.
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- Two wooden rods of different diameters
- Coil wound on one rod
- Inductance meter
A coil of 50 turns is wound onto the larger of two wooden rods. The length of the coil is noted and its inductance is measured. Another 50 turn coil is then wound onto a second rod of approximately 1/2 the cross sectional area while keeping the same length as the first coil. The inductance is measured and compared to that of the first coil.