# Faraday's Law

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## Faraday's Law Answer Key

**Instructions:**
Read each question carefully. Choose the answer that best fits the question. Short answer response questions must be responded to in complete sentences. If the question involves calculations, you must show all your math work.

1.

The Faraday constant is the magnitude of electric charge per and can be used to find the amount of an element that has been oxidized.

- degree K
- mole of electrons
- unit area
- none of the above

2.

In electrolysis, which quantity must be divided by the Faraday constant to determine the number of moles of the element that is oxidized?

- the temperature in degrees
- the electric potential
- the amount of charge
- the total mass of substance

3.

Faraday’s first law of electrolysis says that a substance's mass changed at an electrode during electrolysis is directly proportional to the

- amount of electricity transferred at said electrode.
- temperature of the electrolyte.
- none of the above.

4.

Which quantity must be multiplied by the elementary charge to find the Faraday constant, F?

- Boltzmann constant
- Stefan-Boltzmann constant
- Gas constant
- Avogadro constant

5.

What is the equation for Faraday’s combined laws? Be sure to explain the meaning of each variable.

- [math]m = (Q/F) * (M/z)[/math]

where:

m is the mass of the substance liberated at an electrode in grams

Q is the total electric charge passed through the substance

[math]F = 9.6485xx10^4 C mol^-1[/math] is the Faraday constant

M is the molar mass of the substance

z is the valency number of ions of the substance

6.

What is the value of Faraday's constant? What does it represent?

- [math]9.6485xx10^4C/(mol)[/math]

Faraday's constant represents the magnitude of electric charge per mole of electrons.

7.

According to Faraday’s Law of Induction, the changing magnetic flux through a coil of wire will induce an emf in the wire that is proportional to the number of loops and the rate of change of the magnetic field.

8.

How is Faraday's law expressed in equation form? Be sure to include an explanation of the variables involved.

- [math]emf=−N((ΔΦ_B)/(Δt))[/math], wherein,

emf is the induced emf (V or J/C),

N is the number of turns of coil,

[math]ΔΦ_B[/math] is the change in magnetic flux [math](Tm^2)[/math], and

[math]Δt [/math] is the change in time (s)

9.

Explain, in detail, what a magnetic flux is, how it can be determined, including the equation for it, and how it can be applied to a real world situation.

- Magnetic flux is a measure of the amount of magnetic field passing through a given surface. The magnetic flux through a given surface is proportional to the number of magnetic field lines that pass through the surface. It can be calculated by finding the product of the average magnetic field times the perpendicular area that it penetrates.

Magnetic flux can be given by the equation: [math] Φm=BA[/math],

wherein,

[math]Φm[/math] is the symbol representing magnetic flux, in SI units, weber (Wb) (or volt-seconds);

[math]B[/math] is the magnitude of the average magnetic field; and

[math]A[/math] is the perpendicular surface area through which the magnetic field lines penetrate.

For an electric generator, where the magnetic field penetrates a rotating coil, the area used in defining the magnetic flux is the projection of the coil area onto the plane perpendicular to the magnetic field.

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