Unit 1 - Quantum Phenomena

Question 0

Describe the process by which mercury atoms become excited in a fluorescent tube? (3)

Answer 0

• Electrons/current flows through tube
• Collide with atomic electrons or Mercury atoms
• Raising the electrons to a higher level

Question 1

What is meant by an excited atom? (1)

Answer 1

An electron at a higher level than ground state
Or
An electron moved to a higher level

Question 2

What is the purpose of the coating on the inside surface of the glass in a fluorescent tube? (3)

Answer 2

• Photons emitted from Mercury atoms are ultra-violet
• Photons are absorbed by powder
• Powder emits photons in visible spectrum

Question 3

What is meant by the threshold frequency of the incident light? (1)

Answer 3

Below this frequency no electrons emitted
Or
Minimum frequency for electrons to overcome work function

Question 4

Explain why the photoelectric effect is not observed below the threshold frequency? (2)

Answer 4

• Energy of photon depends on frequency

* Below threshold frequency not enough energy to overcome work function/liberate electron

Question 5

Explain why electrons emitted, from a metal irradiated with ultraviolet radiation of a certain frequency, have a maximum kinetic energy? (2)

Answer 5

• E=hf is energy of photons

* Energy required to remove electrons varies, so kinetic energy varies

Question 6

Explain with reference to the work function why, if the frequency of the radiation is below a certain value, electrons are not emitted. (2)

Answer 6

• Work function is the minimum energy needed to release an electron
• Below a certain frequency the photon’s energy is less than the work function

Question 7

What is an appropriate unit for work function? (1)

Answer 7

Joule

Question 8

What phenomenon can be used to demonstrate the wave properties of electrons? (1)

Answer 8

Diffraction/ interference/ superposition

Question 9

A photon moving through a material can interact with the nucleus of an atom to produce an electron and positron. What is the name of this process? (1)

Answer 9

Pair production

Question 10

In pair production, why could a single electron be produced, instead of an electron and positron? (2)

Answer 10

• Conservation of charge/lepton number

* +1-1=0

Question 11

What happens to the positron produced in pair production? (2)

Answer 11

• Encounters an electron and the two particles annihilate

* Releasing two photons/quanta

Question 12

State what is meant by the ionisation energy of hydrogen. (2)

Answer 12

• Energy required to completely remove an electron from atom

* From the ground state

Question 13

Pair production can occur when a photon interacts with matter. Explain pair production. (2)

Answer 13

• Photon interacts with electron/ nucleus/ atom

* Energy of photon used to create particle and antiparticle pair

Question 14

Explain why pair production cannot take place if the frequency is below a certain value. (3)

Answer 14

• Energy of photon depends on frequency
• If energy is below certain value there is not enough energy…
• …to provide mass/rest energy of particles

Question 15

Energy and mass are conserved during pair production. State two other quantities that also must be conserved. (2)

Answer 15

(Any two)

Charge/ lepton number/ baryon number/ strangeness

Question 16

State what is meant by ground state. (1)

Answer 16

When electrons are in their lowest/minimum energy level

Question 17

Explain the difference between ionisation and excitation. (3)

Answer 17

• In either case an electron received energy
• Excitation promotes an electron to a higher energy level
• Ionisation occurs when an electron receives enough energy to leave the atom

Question 18

An atom can also become excited by the absorption of photons. Explain why only photons of certain frequencies cause excitation in a particular atom. (4)

Answer 18

• Electrons occupy energy levels
• Need to absorb an exact amount of energy to move to a higher level
• Photons need to have certain frequencies to provide this energy
• All photon energy is absorbed

Question 19

State what is meant by the work function. (2)

Answer 19

• Minimum energy required to

* Remove electron from metal

Question 20

Explain why the emitted electrons have a range of energies up to a maximum value. (4)

Answer 20

• Photons have energy dependant on frequency
• One to one interaction between photon and electron
• Max KE= photon energy - work function
• More energy required to remove deeper electrons

Question 21

What is the process called where a photon is converted into an electron and a positron. (1)

Answer 21

Pair production

Question 22

A photon of slightly higher energy than needed is converted into an electron and positron. State what happens to the excess energy. (1)

Answer 22

Kinetic energy

Question 23

Describe what is likely to happen to the positron shortly after its creation. (2)

Answer 23

• Annihilate

* Converting into two or more photons

Question 24

An electron is incident on a hydrogen atom. Explain why the electron in the ground state becomes exited to the next energy level. (2)

Answer 24

• Absorbs enough energy from the the incident electron

* Needed to make the transition up an energy level

Question 25

What effect on electrons emitted from metals does reducing the frequency of the incident radiation have. (2)

Answer 25

• Decreases photon energy

* Decreasing maximum kinetic energy of electrons emitted

Question 26

What effect on electrons emitted from metals does doubling the intensity of the incident radiation have. (2)

Answer 26

• Increase in photons cause increase of electrons

* Double the number of electrons