Question

Why do the voltage and current in the pickup coil cycle between negative and positive? Explain in detail using Faraday’s Law. Remember, Lenz’s Law is part of Faraday’s Law! Although it will not be covered explicitly in this class, this is known as alternating current. Points to discuss: How the magnetic flux through the loop changes as the magnet rotates. Is the flux maximal when the magnet is horizontal or vertical on the screen? Why?) How this changing magnetic flux works to create an emf (potential difference) in the coil which alternates over time (use the Faraday’s law equation)

Answer 1

The voltage and current in the pickup coil cycle between negative and positive because of the reason that

• How the magnetic flux through the loop changes as the magnet rotates.

as the magnet rotates the magnetic flux interacting with the loop changes that is when magnet rotates its one part is near to the loop so flux through the loop increases and when this part goes away flux decreases and this interaction change causes the emf induction.

• Is the flux maximal when the magnet is horizontal or vertical on the screen? Why?

as here the screen position is not given still the maximal position will be when the angel between the area of the coil and magnetic field will be zero because we have the formula as

flux = B.A = BACos (theta)

so here the flux maximal when the angle between the magnetic field and area vector will be zero.

• How this changing magnetic flux works to create an emf (potential difference) in the coil which alternates over time (use the Faraday’s law equation)

Here the alternating nature of the electrons comes into the play so that when the magnetic field of the solenoid changes with the time so it affects the electrons of the pickup coil and as the magnetic field changes so their cycle also changes with the movement of the electrons in the particular direction. As the Faraday law says that any change in the magnetic field will induce emf in the coil and when the coil is a closed path there will be current flowing through it and the direction of this induced emf is given by the Lenz law which says the cause oppose the effect so each time the magnetic field changes the direction or we can say the cycle of the current and voltage will change to oppose the effect the changing magnetic field.

form the faradays law we have mathematically,

e = - d(rate of change of the magnetic flux)

here negative sign shows that emf induced will be in the opposite direction of the magnetic field.