Chapter 8- Charge and Current

Question 1

Current

Answer 1

The rate of flow of charge

Measured in Amperes

Question 2

Charge

Answer 2

A physical property, measured in Coulombs or As

Has two types, positive and negative

Question 3

What do like charges do?

Answer 3

Repel, opposite charges attract

Question 4

What are particles that have an electric charge called?

Answer 4

Charge carriers

Question 5

e

Answer 5

The elementary charge
1.60 X 10^-19 C
The charge of one proton
Electron has charge -1 e
The charge of an object is quantised as it can only be integer values of e

Question 6

Charge flow from number of electrons (n)

Answer 6

Q = +/- ne

Question 7

Millikan’s Oil Drop Experiment

Answer 7

• Sprays tiny drops of oil and allows them to move between a tiny gap between plates
• Used a microscope to focus on one floating down
• Attracted to the positive plate above, repels the negative below, opposite direction to weight
• They adjust the voltage until the forces are balanced and write that down with the mass each time
• They can use that the two forces are equal to find what the factor of each charge ix

Question 8

Modelling current in metals

Answer 8

Regular lattice of positive ions surrounded by free electrons
Electrons are repelled by the negative and attracted by the positive terminal

Question 9

Conventional Current

Answer 9

Positive terminal to negative

Question 10

Electron flow

Answer 10

Negative terminal to positive

Question 11

Current in liquids

Answer 11

• In electrolytes (molten ionic compound/ionic solution)
• Divides into positive ions (cations) and negative (anions)
• When you add electrodes the ions are attracted to the opposite charge

Question 12

Placement of an ammeter

Answer 12

In series (alongside the component whose current you are measuring)
You want it to have the lowest resistance possible to minimise the effect on the total resistance

Question 13

Number density

Answer 13

The number of free charge carriers per unit volume

Question 14

Number density of each classification

Answer 14

Conductors: Very high (mostly metals)
Semiconductors: Inbetween (due to impurities/temperature)
Insulators: Very low or zero

Question 15

Movement of electrons in conductors

Answer 15

Electrons generally move randomly as they are away from the pull of the nucleus
The net movement is from negative to positive

Question 16

Mean drift velocity

Answer 16

The average velocity attained by particles, such as electrons, in a conductor

Question 17

Mean drift velocity equation

Answer 17

I = A n e v
Current = area x number density x elementary charge x mean drift velocity

Question 18

Conservation of charge

Answer 18

Electric charge can be neither created nor destroyed, thus the total charge in the universe will remain constant

Question 19

Kirchhoff’s First Law (Current Law)

Answer 19

At any point in an electrical circuit, the sum of the currents into that point is equal to the sum of the currents out of that point

Question 20

Can you see the direction of current with an ammeter?

Answer 20

Yes, it will give a negative value if it is going in the other direction