Chapter 8 - Charge And Current

Question 1

What is electric current and what is it measured in?

Answer 1

Rate of flow of charge

Amperes (A)

Question 2

What is the equation for electric current?

Answer 2

V=IR
OR
Charge transferred in Coulombs over time
OR
Current = cross sectional area x 1.6x10^-19 x number density x mean drift velocity (m/s) (AneV)

Question 3

What is 1 amp in coulombs?

Answer 3

One coulomb of charge passing a given point per second

Question 4

What is electric charge and what is measured in?

Answer 4

Electrons flowing past a point in one second

Coulombs(C)

Question 5

What is a particle with an electric charge?

Answer 5

A charge carrier

Question 6

What is the charge and the mass of an electron?

Answer 6

Charge is 1.6x10^-19

Mass is 9.11x10^-31

Question 7

What is the charge on an object described as?

Answer 7

Quantised

Question 8

What is an electric current in metals and in liquids?

Answer 8

Liquids - Ions

Metals - Electrons

Question 9

What is the structure of a metal?

Answer 9

Lattice of positive ions surrounded by a number of free electrons

The positive ions vibrate but do not move

Question 10

How do you make the free electrons move in a metal?

Answer 10

Induce a potential difference

Question 11

A larger current may be due to…

Answer 11

A greater number of electrons moving past a point per second

Same number of electrons moving faster

Question 12

Which way does conventional current flow?

Answer 12

Positive to negative

Question 13

Which way do electrons flow?

Answer 13

Negative to positive

Question 14

What are liquids than can carry current?

Answer 14

Electrolytes (Molten ionic compounds or ionic solutions)

Question 15

What is an ammeter used to measure?

Answer 15

Electric current at any point in a circuit

Question 16

Where are ammeters placed?

Answer 16

Directly in series in the circuit

Question 17

How much resistance do ammeters have?

Answer 17

Very close to 0 / Low as possible so it doesn’t effect the current it measures

Question 18

What is Kirchhoff’s first law?

Answer 18

The current in at any point in circuit is equal to the sum of currents out

Question 19

What is number density?

Answer 19

The number of free electrons per cubic metre of material

Question 20

What three groups can materials be classified according to their number density?

Answer 20

Conductors - High number density
Semi Conductor - Between the two
Insulators - Low number density

Question 21

What does a lower number density mean in terms of current?

Answer 21

A lower number density means to carry the same current as a material with a high number density, the electrons need to move faster
This increases temperature

Question 22

How fast do charge carriers move and why?

Answer 22

Slowly because they collide with positive metal ions as they drift through the wire.

Question 23

How does a narrower wire affect mean drift velocity?

Answer 23

Narrow wire means greater drift velocity to maintain same current

Question 24

What is the equation for electric current using number density?

Answer 24

I=Anev

A=cross sectional area
n = number density
e = elementary charge (1.60x10^-19)
v = mean drift velocity