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Flashcards in 4.5 Quantum Deck (26)
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1

What is a quantum?

a small discrete unit of energy

2

What is a photon?

A quantum associated with electromagnetic radiation

3

What is the Planck constant?

h, photon energies are always emitted at multiples of this

4

What is an electronvolt?

the kinetic energy gained by an electron when it is accelerated through a potential difference of 1 volt

5

What is threshold frequency?

the lowest frequency of radiation that will resul in the emission of electrons from a particular metal surface. For most metals = UV

6

Define work function

the minimum energy required to release an electron from its surface, overcoming the electrostatic attraction between the electron and positive metal ions

7

Describe quantum model

EM radiation emitted by hot objects could no have continuous values.
Had to be emitted in packets, that have fixed amounts of energy.

8

What did Newton say about light?

tiny corpuscles, reflection and refraction
move quicker through more dense medium

9

What did Huygens say about light?

Wave
Refraction and reflection
slow down in more dense
predict diffraction

10

What did Young's double slit prove about light?

Wave
Interference to produce fringes

11

What did de Broglie do?

Both wave and particle

12

How do you calculate the energy of a single photon?

E = hf or E=hc/wavelength

13

How do we calculate the energy gained by a proton?

charge x potential difference

14

What is 1 eV equal to?

1.602 x 10^-19

15

Convert from eV to J?

multiply by 1.602x10^19

16

What did Einstein say about the work function

For electrons to be released,, the frequency of the incident radiation must exceed the threshold frequency for that energy

17

What happens when incident radiation is above threshold frequency?

Electrons emitted with some kinetic energy

18

Why can the photoelectric effect not be explained using a wave model?

energy of a wave depends on its amplitude (intensity), not its frequency

19

Why can we not notice the wave nature of large objects?

Diffraction needs to occur
Wavelength must be equal to gap of an object that radiation passes through
For big objects at slow speeds this is too small

20

What condition is necessary to produce observable electron diffraction when passing through matter?

Wavelength of electrons must be comparable to order of magnitude of atomic spacing

21

Whey in an electron gun, is the cathode connected to the negative terminal of the supply?

Electrons should be repelled by cathodes. Would be slowed down if cathode was positive

22

How can you demonstrate the photoelectric effect?

Clean zinc plate gold leaf electroscope
Negatively charged
UV light
Gold leaf collapses and charge moves away
Indicates emission of electrons

23

Photoelectric effect in terms of quantum behaviour

Individual photons absorbed by individual electrons
Overcome work function
Instantaneous emission
Number of electrons depends on light intensity
Einsteins photoelectric equation

24

Explain photoelectric effect

Only about threshold frequency
Einsteins equation
Work function is minimum energy
Number of electrons is higher at higher intensity
Emission is instantaneous

25

Explain what the de Broglie wavelength of an electron is?

Electrons are observed to behave as waves where wavelength depends on speed/momentum

26

What effect does doubling intensity have on the energy of a photon?

Photon energy does not change.
Only changes when frequency changes
Greater intensity = more photons incident