19: Quantum

Question 1

Define a photon

Answer 1

A photon is a quantum energy of electromagnetic radiation

Question 2

Define work function energy

Answer 2

Work function energy of a metal refers to the minimum amount of energy that an electron requires to remove it from the metal surface

Question 3

Define Threshold frequency

Answer 3

Threshold frequency of a photon refers to the minimum frequency required for incident photon such that it posses sufficient energy to remove an electron from the metal surface

Question 4

Define stopping potential

Answer 4

Stopping potential refers to minimum pd between the metal and collector that will prevent the most energetic photoelectron from reaching the collector

Question 5

State equation for intensity quantum

Answer 5

intensity = (number of photons incident/t)(hf/A)

Question 6

State equation for saturation current

Answer 6

I sat = (Number of electrons emitted/t)(e)

Question 7

Explain existence of threshold frequency

Answer 7

wave theory predicts: energy transfer is continuous
quantum theory shows: photons with freq below a certain value, no electrons emitted

Question 8

Explain no time delay in emission of photoelectrons

Answer 8

Wave theory predicts: low intensity, there is time lag because time required to accumulate sufficient energy
Quantum theory: As long as freq of light > th freq, electrons have enough energy and instantly escape surface. This is because each electron can only absorb one photon, thus regardless of intensity of incident light as long as freq light > th freq, electrons will escape immediately

Question 9

Explain stopping potential/(KE max) independent of incident light

Answer 9

wave theory predicts: if intensity of light increase, electrons will have higher energy and escape with higher KE
quantum theory explains: Higher intensity at constant frequency will only increase number of incident photons but not energy that photons escape with as energy of photon remains the same

Question 10

Explain photocurrent proportional to intensity of incident light at constant frequency

Answer 10

wave theory predicts: higher intensity, higher energy per unit area and thus more electrons escape this is wrong as one electron will only absorb one photon

quantum theory explains: Increase intensity at constant frequency, number of incident photons at metal surface increases, thus more electrons will absorb photon and gain sufficient energy to escape metal surface, thus more photoelectrons emitted and thus current rises

Question 11

Define Energy level

Answer 11

Energy level is the discrete energy corresponding to an allowed state of the electron within the atom

Question 12

Explain how Emission line spectrum and Absorption line spectrum is formed

Answer 12

i ain’t writing everything out man

Question 13

How does X-ray work?

Answer 13

1. Cathode heated and emitted electrons
2. High pd set across cathode and target metal to accelerate electrons
3. High speed electrons bombard the target metal
4. Electrons lose a range of KE and the energy lost is emitted to surroundings as photons
5. Photons has frequency of xrays