C8 Charge and Current

Question 1

Define Coulomb

Answer 1

• The electric charge flowing past a point where there is an electric current of one ampere applied for one second.

Question 2

Definition for electrical current

Answer 2

• The rate of flow of electric charge past a point in a circuit, measured in amperes.

Question 3

Elementary Charge, subsequently charge on a single proton & electron

Answer 3

1.60 x 10^-19
Proton: 1.60 x 10^-19
Electron: -1.60 x 10^-19

Question 4

Why is charge described as being quantised?

Answer 4

It can only take on certain discrete values, multiples of the elementary charge.

Question 5

Conventional Current Vs Electron Flow, and why conventional current exists

Answer 5

• Conventional current moves from positive to negative.
• Electron flow is from negative to positive.
• The direction of conventional current was defined long before the discovery of the electron.

Question 6

Number Density Definition

Answer 6

• The number of free charge carriers per unit volume.

Question 7

Examples of Insulators, Semiconductors, and Conductors.

Answer 7

Insulators: Wax, Rubber
Semiconductors: Silicon, Germanium
Conductors: Lead, Zinc, Copper

Question 8

Define Drift Velocity, and formula to calculate it

Answer 8

• The average velocity of charge carriers through a conductor in response to an applied electric field.

I = Anev
v = I / Ane

A = cross sectional area
n = number density
e = elementary charge
v = mean drift velocity

Question 9

Relationship between drift velocity and cross sectional area

Answer 9

• Drift Velocity is inversely proportional to the area.
• If the area decreases, drift velocity increases. The electrons move faster in order to carry the same charge.

Question 10

Number of electrons in one coulomb charge

Answer 10

6.25 x 10^18