Module 4 Chapter 1 Electricity: Charge and Current

Question 1

What two forms can the property ‘charge’ take?

Answer 1

Positive and negative.

Question 2

What is the charge of an electron?

Answer 2

Negative.

1.6 * 10^-19 C

Question 3

What unit is charge measured in?

Answer 3

Coulombs (C)

Question 4

What is electrical current?

Answer 4

A flow of charged particles such as electrons or ions.

Question 5

How can you calculate current based on charge?

Answer 5

I = ΔQ/Δt
current = change in charge / change in time

Question 6

What carries the current in all metals?

Answer 6

Delocalised electrons.

Question 7

What carries the current in electrolytes?

Answer 7

Dissolved ions.

Question 8

What is Kirchhoff’s first law?

Answer 8

The sum of the currents entering a junction is equal to the sum of the currents exiting a junction.
This is also true for charge.

Question 9

What does the conservation of charge mean?

Answer 9

Charge cannot be created or destroyed, only transferred. therefore, it is conserved.

Question 10

How can you calculate charge based on current?

Answer 10

Q = I*t
charge = current * time

Question 11

How can you calculate current using the charge of an electron?

Answer 11

I = n*e
current = number of electrons per second * the charge of an electron (1.6 * 10^-19 C)

Question 12

How can you calculate charge over a period of time using the charge of an electron?

Answer 12

Q = n*e*t
charge = number of electrons per second * the charge of an electron (1.6 * 10^-19 C) * time in seconds

Question 13

How do calculate mean electron drift velocity?

Answer 13

v = I/(n*A*e)
v = mean electron drift velocity
I = current
n = density of free electrons
A = cross-sectional area of the wire
e = the charge of an electron (1.6 * 10^-19 C)

Question 14

How do you calculate current using electron drift velocity?

Answer 14

I = A*n*e*v
I = current
A = cross-sectional area of the wire
n = density of free electrons
e = the charge of an electron (1.6 * 10^-19 C)
v = mean electron drift velocity

Question 15

What is the relationship between the density of free electrons in a material and its ability to conduct material.

Answer 15

The greater the density, the better an electrical conductor the material is.

Question 16

What would be a typical density of free electrons in a conductor?

Answer 16

4.6 * 10^28 (calcium) to 1.8 * 10^29 (aluminium)

Question 17

What would be a typical density of free electrons in a semiconductor?

Answer 17

2.0 * 10^6 (gallium arsenide) to 2.0 * 10^13 (germanium)

Question 18

What would be a typical density of free electrons in an insulator?

Answer 18

close to zero.