Suppose you find a new material. It is a conductor, but you don\'t know whether

Question

Suppose you find a new material. It is a conductor, but you don't know whether the charge carriers have positive or negative charge Explain what you could do to determine this. We have learned that a metal bar moving in a constant magnetic field can be used to drive a current in a circuit. Explain what happens to prevent this from being a perpetual motion machine. In a circuit with a battery and a resistor, a current flows even if the battery is so far from the resistor that the electric field from the battery is negligible. How is this possible? When you connect a battery, a resistor, and a capacitor in series, the current has an initial value but then decreases with time. Explain why this happens. Two parallel wires conduct a current in opposite directions. Explain what happens to the wires and why.

Explanation / Answer

1) put a voltage across the conductor to get current flowing and then

put a magnetic field perp to the voltage

if positive they will go one way if negative the other

this is called a Hall experiment.

2) the current you produce will have a force in the magneticfield
which will slow you down

3) current across the whole wire moves so for some charges to move by the battery some far away have to move.

4) the capacitor is becoming charged and as it does so it lets less current through

5)

so one wire will make a field at the other wire which will feel a force

Lets say left is into the page and right is out of the page

the left one will make a field down

then I into B gives a force to the right

so wires are repelled

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