Particles and radiation

Question 1

What is the photoelectric affect?

Answer 1

Where photoelectrons are emitted from the surface of a metal after light above a certain frequency is shone on it.

Question 2

What is threshold frequency?

Answer 2

The certain frequency for the photoelectric affect to occur on different metals

Question 3

What does the photon model of light suggest?

Answer 3

• EM waves travel in discrete packets called photons, which have an energy which is directly proportional to energy
  -Each electron can absorb a single photon, therefore a photoelectron is only emitted if the frequency is above the threshold frequency
  -If the intensity of the light is increased, if the frequency is above the threshold, more photoelectrons are emitted per second

Question 4

What is work function of a metal?

Answer 4

The minimum electrons to be emitted from the surface of a metal

Question 5

What is the stopping potential?

Answer 5

The potential difference you would need to apply across the metal to stop photoelectrons with the maximum kinetic energy.

Question 6

What is the equation for the maximum kinetic energy of a photoelectron?

Answer 6

maximum kinetic energy of photoelectron = charge of an electron * stopping potential

Question 7

What is the photoelectric equation?

Answer 7

energy of photon = Planck constant*frequency = work function + maximum kinetic energy of photoelectron

Question 8

What do electrons in atoms exist in?

Answer 8

discrete energy levels

Question 9

What happens during the excitation of an electron?

Answer 9

An electron has gained energy from a free electron and has moved up an energy level

Question 10

What happens during the ionisation of an electron and how does it occur?

Answer 10

When an electron gains enough energy to be removed from an atom entirely. Only occurs when the energy of the free electron is greater than the ionisation energy

Question 11

What happens after excitation of an atom?

Answer 11

It will quickly return to its original position (ground state) and releases its energy gained in the form of a photon

Question 12

What is contained within a fluorescent tube and what is applied across it?

Answer 12

Mercury vapour and a high potential difference is applied across the tube.

Question 13

Describe how a fluorescent tube works

Answer 13

-voltage accelerates free electrons across the tube
-Free electrons collide with the mercury atoms causing them to become ionised and release more free electrons
-The free electrons collide with the mercury atoms causing them to become exited.
-When they de-excite photons are emitted most of which are in the UV range
-The fluorescent coating (phosphorous) on the inside of the tube absorbs the UV photons.
-Therefore the atoms in the coating excite and then de-excite releasing photons of visible light

Question 14

What unit is used when describing the difference in energy levels?

Answer 14

electron volt

Question 15

What happens if you pass the light emitted from a fluorescent tube through a diffraction grating or prism?

Answer 15

Get a line spectrum of discrete values of wavelength

Question 16

What does a discrete line spectrum provide evidence for?

Answer 16

-Each discrete value shows that only a wavelength of that value is emitted
-Therefore the only photon energies emitted correspond to these wavelengths
-Therefore this is evidence to show that electrons in atoms can only transition between discrete energy levels.

Question 17

What happens in an absorption spectrum?

Answer 17

Continuous spectrum with black lines at certain wavelengths

Question 18

What do the black lines represent in an absorption spectrum?

Answer 18

represent the possible discrete energy levels as atoms in the gas can only absorb protons of energy equal to the exact difference between two energy levels.

Question 19

What is the equation for the difference between two energy levels?

Answer 19

E=hf=E1-E2