4.1 Charge and current

What is the unit for charge?

Coulomb (C)

How do you find the exact number of electrons from the charge?

Divide it by e

What can n also be written as?

no. electrons present / volume

What is the value of the charge of the proton, which can also be referred to as the elementary charge e?

1.6×10^−19 C

What is the charge of an electron, which can also be referred to as -e?

-1.6×10^−19 C

What does n represent is this equation Q=−ne?

The number of extra electrons

What does n represent is this equation Q=ne?

The number of electrons lost

What does quantised mean?

The charge of the object has to be a multiple of e

What is electric current?

The rate of flow of charge

What does a current of 1A mean?

A flow of 1C of charge per second

What does an ideas ammeter have?

0 resistance

What are the charge carries in metals?

Free electrons

What are the charge carries in an electrolyte?

Ions

What is the conventional current?

When the current flows form the positive terminal of the power supply to the negative terminal

What was around the circuit do electrons flow?

From the negative terminal of the power supply to the positive

What is the motion of the electrons in a wire without current flowing?

They move randomly at high speeds in a zig-zag motion

What is mean drift velocity?

The low average speed of charge carriers along a conductor when there is a potential different along the conductor

What formula is used to calculate mean drift velocity?

I=Anev

What is the average flow of charge when a circuit has no p.d.?

The random movements of the electrons cancel out and the average flow is 0

What does each letter mean in I=Anev?

• I is the current

• A is the cross sectional area

• n is the number of free charge carriers per unit volume of material

• e is the charge of one charge carrier

• v is the mean drift velocity

How much n do conductors have?

Very high values

How much n do semi-conductors have?

Very low values

How much n do insulators have?

Middle values

What is the law of conservation of charge?

Charge cannot be created or destroyed ∴ the amount in a closed system remains the same

What does the law of conservation of charge mean?

• Charge cannot get used up or lost when it flows around a circuit

• The amount of charge passing though a component per second is constant

• The current entering a component is the same as the current leaving it

• The current passing through two or some components in series is the same

What is Kirchoff’s first law?

The total current leaving a junction is equal to the total current that entered the junction

What causes semi-conductors to have a higher current?

An increase in its temperature, which leads to an increase in its n

How do you calculate the number of electrons?

∆Q/charge on 1 electron (e)

Describe and explain how the mean drift velocity changes as the electrons move

As area increases the mean drift velocity decreases as according to I = nAve

Since the wires are made of the same material and connected in series I, n and e are constant (wtte)

v ∝ 1/A

What happens when the wire is heated up?

The resistance increases as free electrons have more collisions with positive ions

More energy is transferred to the lattice

What is a semiconductor?

A material where the number of charge carriers / free electrons per unit volume / number density changes depending on the conditions.

What happens to the mean drift velocity if the temperature increases, assuming current stays the same

n would increase, v would decrease