Chapter 8

Question 1

Define current

Answer 1

The rate of flow of charge per second

Delta Q
————
Delta T

Question 2

What is a coulomb?

Answer 2

Electric charge flowing past a point in 1 second if current is 1 amps

Question 3

Define charge

Answer 3

A property that can be positive or negative

Electrons ions and protons are charge carriers

Question 4

What is the charge of an electron?

Answer 4

-1.6 x10^-19 coulombs

Question 5

How many electrons make up 1 coulomb?

Answer 5

1/1.6x10^-19 = 6.25 x10^18 electrons

Question 6

Why is charge described as quantised?

Answer 6

Because it can only have specific values

Question 7

What is electric current?

Answer 7

The flow of charge or movement of charge carriers(protons, electrons or ions

Question 8

What is current in metals?

Answer 8

Flow of electrons from the negative end to the positive end. Metal atoms are fixed while delocalised electrons can carry charge

The structure of metals is a regular lattice of positive ions with delocalised electrons. Vibrations of ions increases temp

Question 9

What happens if charge flow is faster?

Answer 9

Current is greater which means more electrons move past a point per second

Question 10

Where does conventional current flow?

Answer 10

Positive terminal to negative(opposite to direction of electron flow(charge flow))

Question 11

What are electrolytes?

Answer 11

Liquids that carry an electric current through ions. They are molten ionic compounds or ionic solutions

Question 12

Why is electrolysis a current?

Answer 12

Negative ions go to the anode and positive ions go the the cathode. The movement of ions is the flow of charge

Positive ions accept electrons and negative ions donate electrons which flow around the circuit

Question 13

What a conservation of charge?

Answer 13

Electric charge cannot be created nor destroyed. Electric charge in the universe is constant

Question 14

What is Kirchhoff’s first law?

Answer 14

Charge and current is conserved. At any point in a circuit, sum of current going in = sum of current going out

Question 15

What is number density?

Answer 15

The number of free charge carriers per cubic metre of a material.

Higher number density means it’s a better conductor

Question 16

What number density do conductors have and give some examples

Answer 16

They have a number density of 10^28 m^3 order of magnitude. Examples are lead, zinc, copper.

They are metallically bonded so there are a lot delocalised electrons

Question 17

What number density do semiconductors have and why?

Answer 17

They have lower than conductors with order of magnitude of 10^17m^-3.
Usually group 4 elements: they covalently bond with no free electrons
As you heat it up, some bonds start breaking which releases electrons

Question 18

How do semiconductors conduct?

Answer 18

They are covalently bonded in a lattice structure. As temperature melts, more bonds break which releases electrons. So current increases with temperature increase

Question 19

What is the number density of insulators?

Answer 19

Close to 0

Question 20

Define mean drift velocity

Answer 20

The average velocity of charged particles

Question 21

What is the formula for mean drift velocity?

Answer 21

I = ANEV

Question 22

How is mean drift velocity like in conductors, semiconductors and insulators

Answer 22

In a conductor there is a large value of N so drift velocity is small even if there is a large current
In a semiconductor, N is slightly smaller so V is higher
An insulator has N close to 0 and current is not able to flow

Question 23

What happens if cross sectional area halves?

Answer 23

Mean drift velocity doubles for the same current