2.1.1. Charge and Current

Question 1

Define Electric Current.

Answer 1

A net flow of charged particles. Magnitude equal to the rate of flow of charge.

Question 2

Define Conventional Current.

Answer 2

The direction of flow of positive charge: positive to negative.

Question 3

Define Electron Flow.

Answer 3

The direction of negative charge: negative to positive.

Question 4

What is Kirchhoff’s 1st Law?

Answer 4

The sum of the currents entering a junction any point in a circuit is equal to the sum of the currents leaving that junction. A consequence of the conservation of charge.

Question 5

Define Drift Velocity.

Answer 5

When an applied electric field gives randomly moving electrons a small net velocity in one direction.

Question 6

Describe Ohmic Heating.

Answer 6

• Electrons collide with metal ions in metal lattice.
• Kinetic energy gained from being accelerated by electric field is transformed to the ions.
• This increases the vibrational energy of the lattice, therefore also the temp of the conductor and electric current too.

Question 7

Describe Electron Motion.

Answer 7

When an electric field is applied, electrons gain a net movement towards the positive terminal. They collide with metal ions and thus pass on their kinetic energy.

Question 8

Define the symbols in I = nAVe

Answer 8

I = Current / A
n = Number density / m^-3
A = Cross-sectional area
v = Drift velocity / ms^-1
e = Electron charge / C

Question 9

State the Elementary Charge possessed by protons and electrons.

Answer 9

1.6 x 10 ^-19 C

Question 10

Define the Root Mean Square Velocity of charge carriers.

Answer 10

The random velocity of charge carriers due to their thermal energy and electrostatic interactions, typically 10^6ms^-1.

Question 11

Describe Electron Drift in an Electrolyte.

Answer 11

An electrolyte contains both positive and negative ions. When electrodes are placed in a solution of these ions, negative ions move to positive electrode and vice versa.

Question 12

Define Number Density, n.

Answer 12

The number of free charge carriers per unit volume, measured in m^3.

Question 13

Define a Conductor.

Answer 13

Having low resistance and high charge carrier density.

Question 14

Define an Insulator.

Answer 14

Having a high resistance and very low charge carrier density.

Question 15

Define a semiconductor.

Answer 15

Having a charge carrier density that lies between that of a conductor and insulator. The value of n increases eith increasing temperature i.e. it’s a conductor when warm and an insulator when hot.

Question 16

Define the coulomb.

Answer 16

The amount of charge that passes a fixed point in a circuit in 1 second when a current of 1A flows.