Physical lecture 3

Question 1

Give the equation for potential energy (V) of an electron and explain the terms

Answer 1

V = -e^2/4⫪ε0r
e is the fundamental charge
ε0 is the permittivity of free space
r is the radius

Question 2

State the two types of energy an object can have

Answer 2

Kinetic and/or potential

Question 3

Describe kinetic energy and give its equation

Answer 3

Kinetic energy is energy due to movement, and is equal to 1/2mv^2

Question 4

Describe potential energy (V)

Answer 4

V is energy because of a position in a field. It is a relative quantity and is calculated by how much work is takes to move the object from a defined ‘zero state’.

Question 5

Describe the zero state and potential energy of the hydrogen atom.

Answer 5

‘Zero State’ is defined as infinite separation. As the electron gets closer to the nucleus, P.E becomes negative. Work has to be done on the system to separate the electron and the proton; work done to move an electron from a distance r from the nucleus to infinite separation is measured in joules and equal to -V

Question 6

State coulomb’s law and explain its use and its terms

Answer 6

F = q1q2e^2/4⫪ε0r^2
This equation tells us about the force between two charged species.
q1 = +1 for every proton and
q2 = -1 for every electron
r is the distance from the nucleus
The rest of the terms can be written as a constant k.

Question 7

State Bohr’s postulate relating to the quantisation of the angular momentum of the electron

Answer 7

Bohr said the angular momentum of the electron had to have values of multiples of h/2⫪, = ℏ. Ie nℏ where n was the quantum number. Note; if we rearrange this to get v, it is shown that the velocity of the orbiting electron is also quantised.