Help with physics?

Posted on 2015-11-23 07:19:00 in Physics by EDEN

Inductive loops at traffic lights can be adjusted to detect bicycles with metal rims. Below is a
simplified diagram of a bike waiting for the traffic lights to change.
rim of bicycle wheel
wire
direction of
magnetic field
around the wire at
one instant
The inductive loop circuit uses Faraday’s law to detect changes in the inductance when a
bicycle is above the circuit. The high-frequency, alternating current induces a magnetic field
in the metal bicycle rim. The magnetic field induced in the bicycle rim reduces the overall
magnetic field. The inductance of the circuit is reduced, and this is detected by the traffic
lights.
Explain the underlying physical concepts used in this situation.
In your answer you should:
• describe the nature of the magnetic field that is created by the alternating current in the
wire
• explain why a high-frequency alternating current is needed to induce a significant
magnetic field in the rims of the bicycle wheels
• explain why the induced magnetic field in the rims of the bicycle wheels is in the
opposite direction to the magnetic field around the wire

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