Quantum

Question 1

Explain why energy levels are negative

Answer 1

• To remove an electron (reach 0 energy) energy has to be supplied

Question 2

Explain how
• the bombarding electrons cause the atoms of the vapour to emit photons
• the existence of a spectrum consisting of lines of a definite frequency supports the view that atoms have discrete energy levels.

Answer 2

The high energy electrons bombard atoms of vapour, interact with atomic orbital electrons and give energy to to those electrons. If an orbital electron recieves enough energy to move to a higher energy and there is a vacant state for it, it will be ‘prmoted’ to the higher energy level. Such an electron is called an ‘excited electron’.
Excited electrons move down to lower energy levels, losing energy by emitting photons of energy specific to the energy difference between the energy levels. Photons have energy that is calculated by E=hf, therefore photons of characteristic frequencies are emitted from atoms of a particular element. Therefore only discrete lines are observed on the spectrum.
(6 marks)

Question 3

~Describe how the concept of energy levels is useful in explanation of line spectra

Answer 3

• Electrons can only exist in discrete energy levels
• energy moves up + down which corresponds to line spectra
• Each line represents a definitive wavelength

Question 4

-Discuss how the discharge tube is made to emit electromagnetic radiation of specific frequencies;
In your answer you should
-explain why there must be a high P.D across the tube
-Discuss how

Answer 4

Yhtyyu

Question 5

Identify the state of an electron in energy level 0.

Answer 5

Ionising state

Question 6

Identify the state of an electron in energy level -13.6ev.

Answer 6

Ground state

Question 7

Discuss how the discharge tube is made to emit electromagnetic radiation of specific frequencies;

Answer 7

1) - P.d allows (electron) to accelerate through the tube
- They then collide with electrons in the atom
- the p.d is needed to cause this excitation.
- Electrons then dexcite
2) To emit photons, excited (e) deexcite + move to a lower energy energy level. Each movement between levels emit a photon of light
- Photons sitting within visible spectrum due to (e) dexciiting to -3.4ev level.
- E= hc/ wavelength calculate
- Long wavelength due to small energy change.

Question 8

Any dexcitiation to ground state; What EM wave produced?

Answer 8

-ultraviolet light

Question 9

Any dexcitation to 1st energy state; What wave is emitted?

Answer 9

-Visible light

Question 10

How does threshold frequency give evidence against the wave theory of light?

Answer 10

• If light only acted as a wave, e in metal would slowly absorb energy of incident light waves until enough energy to escape.
• no matter how the frequency of light varied-there would be no threshold observed

Question 11

Why is monochromatic light better?

Answer 11

Clearer in diffraction as coherent same wavelength

Question 12

One real life application of diffraction gratings in real life

Answer 12

Observing elements in stars using absorption spectra

Question 13

How to overcome modal dispersion

Answer 13

Can be reduced by using single-mode fibre, which only lets light take a narrow path