13 - Quantum physics

Question 1

What is the relationship between photon energy and frequency?

Answer 1

Photon energy ∝ Frequency;
E = hf
where E = Photon energy (J)
h = Planck’s constant (Js)
f = Frequency (Hz)

Question 2

Describe another way to express the energy of a photon.

Answer 2

The energy of a photon can be expressed in terms of it’s wavelength and c (speed of light through a vacuum).

Question 3

What is the energy of 1 electronvolt?

Answer 3

The energy of 1 electronvolt is defined as the energy transferred to or from an electron travelling through a potential difference of 1 V.

Question 4

How do you convert between J to eV?

Answer 4

To convert from J to eV, divide by 1.6 x 10⁻¹⁹

To convert from eV to J, multiply by 1.6 x 10⁻¹⁹

Question 5

What are the three key observations of the photoelectric effect?

Answer 5

• Photoelectrons were emitted only if the incident radiation was above a certain frequency (f0 - threshold frequency), regardless of the radiation intensity.
• If the incident radiation was above the f0, emission of photoelectrons was instant.
• If the incident radiation was above the f0, increasing the intensity did not change photoelectron kinetic energy, but increased the quantity of electrons emitted. The only way to increase the kinetic energy is to increase the incident radiation frequency.

Question 6

What is Ionisation?

Answer 6

When an atom loses an orbiting electron (and becomes charged because protons > electrons), making it a positive ion.

Question 7

What is Excitation?

Answer 7

An electron is raised to a higher energy level but remains within the atom.

Question 8

What is the ground state?

Answer 8

The lowest energy level of an atom.

Question 9

What is the Excited state?

Answer 9

When one or more of an atom’s electrons moves to an outer shell at higher energy.

Question 10

State what is meant by a photon.

Answer 10

A photon is a packet of electromagnetic radiation, the energy of which is directly proportional to it’s frequency.