Analyse qualitatively examples of Faraday's and Lenz's law including the generation of the emf force Flashcards
What is Emf?
The electromotive force of a device is the work per unit charge that the device does in moving charge from its low potential terminal to a high potential terminal.
What is the other formula for emf?
epsilon = Work/charge
What is the misconception surrounding emf?
EMF is not a force, but rather a potential difference in volts (voltage like quantity)
What is Faraday’s experiment show?
- No battery supplying energy to the loop of the wire
- Initially no current is measured in the loop when magnet is held stationary to loop.
- When we move the magnet towards the loop, a current is induced in the loop, shown in the ammeter. When it stops moving, it falls back to zero.
- When you pull the magnet from the loop, an induced current is registered in the opp direction.
What is the current produced in the loop called?
Induced current
What is an induced emf?
The work done per unit charge to produce the current
What is induction?
The process of producing current and emf
What did Faraday conclude from his experiement?
An EMF is induced in the loop when the number of magnetic field lines pass through the loop is changing.
What is important to note in Faraday’s experiment?
The actual number of field lines passing through the loop does not matter, but the actual rate at which the number of field lines change matters
What happens when you move the magnet towards the loop?
As we move the north pole closer to the pole, the number of the field lines increases. The increase in electrons shows the induced current and produces an induced emf for their motion.
What occurs when the magnets stops moving?
The number of field lines through the loop no longer
changes and the induced current and induced emf disappear.
What is the mathematical relationship of emf?
emf = - delta flux//delta time = -delta (BAcos(theta))// delta time
What is Faraday’s Law of induction in words?
The magnitude of the induced emf in a conducting loop is equal to the rate at which the
magnetic flux through that loop changes with time.
If we have multiple loops in a coil, what do we do?
We just calculate the total amount of emf produced
What does faster motion of the magnet do?
Faster motion produces a greater current
State the effect on the current when it appears in relation to the magnet.
A current appears only if there is relative motion between the loop and the magnet (one
must move relative to the other); the current disappears when the relative motion between
the ceases
Explain why faster motion in relation to the formula:
If the relative velocity between the loop and the magnet doubles, the rate of change of flux
doubles, because for the same change in magnetic flux, TU halves. Therefore, the induced
emf doubles.
(refer to formula sheet)
