Faraday's discovery and law
Answers
Answer:
Faraday discovered that if the magnetic field through a loop of wire varies in time then an emf is induced around the loop.
This law, which is known as Faraday's law of magnetic induction
The emf induced in a circuit is proportional to the time rate of change of the magnetic flux linking that circuit.
Explanation:
Faraday's First Law of Electrolysis:-
The mass of the substance (m) deposited or liberated at any electrode is directly proportional to the quantity of electricity or charge (Q) passed.
Faraday's Second Law:-
It states that, “When the same quantity of electricity is passed through different electrolytes, the masses of different ions liberated at the electrodes are directly proportional to their chemical equivalents (Equivalent weights).
Answer:
Electromagnetic induction is the process by which a current can be induced to flow due to a changing magnetic field.
In our article on the magnetic force we looked at the force experienced by moving charges in a magnetic field. The force on a current-carrying wire due to the electrons which move within it when a magnetic field is present is a classic example. This process also works in reverse. Either moving a wire through a magnetic field or (equivalently) changing the strength of the magnetic field over time can cause a current to flow.
How is this described?
There are two key laws that describe electromagnetic induction:
Faraday's law, due to 19ᵗʰ century physicist Michael Faraday. This relates the rate of change of magnetic flux through a loop to the magnitude of the electro-motive force \mathcal{E}E induced in the loop. The relationship is
\mathcal{E} = \frac{\mathrm{d}\Phi}{\mathrm{d}t}E=
dt
dΦ
The electromotive force or EMF refers to the potential difference across the unloaded loop (i.e. when the resistance in the circuit is high). In practice it is often sufficient to think of EMF as voltage since both voltage and EMF are measured using the same unit, the volt. Explain
Lenz's law is a consequence of conservation of energy applied to electromagnetic induction. It was formulated by Heinrich Lenz in 1833. While Faraday's law tells us the magnitude of the EMF produced, Lenz's law tells us the direction that current will flow. It states that the direction is always such that it will oppose the change in flux which produced it. This means that any magnetic field produced by an induced current will be in the opposite direction to the change in the original field.
Lenz's law is typically incorporated into Faraday's law with a minus sign, the inclusion of which allows the same coordinate system to be used for both the flux and EMF. The result is sometimes called the Faraday-Lenz law,
\mathcal{E} = -\frac{\mathrm{d}\Phi}{\mathrm{d}t}E=−
dt
dΦ
In practice we often deal with magnetic induction in multiple coils of wire each of which contribute the same EMF. For this reason an additional term NNN representing the number of turns is often included, i.e.
\mathcal{E} = -N \frac{\mathrm{d}\Phi}{\mathrm{d}t}E=−N
dt
dΦ
What is the connection between Faraday's law of induction and the magnetic force?
While the full theoretical underpinning of Faraday's law is quite complex, a conceptual understanding of the direct connection to the magnetic force on a charged particle is relatively straightforward.
Consider an electron which is free to move within a wire. As shown in figure 1, the wire is placed in a vertical magnetic field and moved perpendicular to the magnetic field at constant velocity. Both ends of the wire are connected, forming a loop. This ensures that any work done in creating a current in the wire is dissipated as heat in the resistance of the wire.
A person pulls the wire with constant velocity through the magnetic field. As they do so, they have to apply a force. The constant magnetic field can’t do work by itself (otherwise its strength would have to change), but it can change the direction of a force. In this case some of the force that the person applies is re-directed, causing an electromotive force on the electron which travels in the wire, establishing a current. Some of the work the person has done pulling the wire ultimately results in energy dissipated as heat within the resistance of the wire.
Faraday's experiment : Induction from a magnet moving through a coil
The key experiment which lead Michael Faraday to determine Faraday's law was quite simple. It can be quite easily replicated with little more than household materials. Faraday used a cardboard tube with insulated wire wrapped around it to form a coil. A voltmeter was connected across the coil and the induced EMF read as a magnet was passed through the coil.
Magnet at rest in or near the coil: No voltage observed.
Magnet moving toward the coil: Some voltage measured, rising to a peak as the magnet nears the center of the coil.
Magnet passes through the middle of the coil: Measured voltage rapidly changes sign.
Magnet passes out and away from the coil: Voltage measured in the opposite direction to the earlier case of the magnet moving into the coil.
An example of the EMF measured is plotted against magnet position.
These observations are consistent with Faraday's law. Although the stationary magnet might produce a large magnetic field, no EMF can be induced because the flux through the coil is not changing. When the magnet moves closer to the coil the flux rapidly increases until the magnet is inside the coil. As it passes through the coil the magnetic flux through the coil begins to decrease. Consequently, the induced EMF is reversed.