Chapter 4 - Particles of Light [Complete]

Question 1

What is the photoelectric effect?

Answer 1

The ability for a negatively charged material, such as a negatively charged zinc plate, to release electrons if they receive a wavelength of light that is above their threshold frequency

Question 2

What is a photoelectron?

Answer 2

An electron that is emitted during or as a result of the photoelectric effect

Question 3

What is the value for Planck’s constant?

Answer 3

6.6 x 10^-34

Question 4

Does UV have a higher or lower frequency than visible light?

Answer 4

Higher

Question 5

What is the kinetic energy of a released photoelectron dependent on?

Answer 5

The frequency of the incident photon

Question 6

What is the equation linking together Planck’s constant, frequency and energy?

Answer 6

Energy = frequency x Planck’s constant

Question 7

What is intensity?

Answer 7

The rate of energy transfer per unit area

Question 8

Explain the potential well model.

Answer 8

• Electrons are visualised as being within a well of energy when they are embedded in an atom or ion, they need a greater, set amount of energy to get out the attraction of the nucleus // - Photons are able to transfer energy to electrons by colliding with them // - Work function is overcome and remainder is kinetic energy // - Person cannot get out of the hole with two smaller jumps - akin to electron cannot get out with two smaller below threshold photons // - E = hf

Question 9

What is the work function?

Answer 9

The least energy needed to release a photoelectron from a material. It is the same as the threshold energy

Question 10

What is Einstein’s photoelectric equation?

Answer 10

hf = work function + 1/2mv[max]^2

Question 11

What is the work function below which the photoelectrons can be released by visible light?

Answer 11

3.1 eV

Question 12

What is the work function below which the photoelectrons can be released by infrared light?

Answer 12

1.77 eV

Question 13

How is stopping potential calculated and what does it tell you?

Answer 13

Stopping potential is calculated by using a photoelectric cell in which there is a positively charged and negatively charged plate on each side. When light strike the surface of the positively charged plate, the electrons are released and start to move towards the opposite plate. However, since this plate is negatively charged, they slow down and come to a stop before they hit it. This stopping potential represents the kinetic energy of the electrons, and is calculated using the equation 1/2mv^2 = eV

Question 14

What did De Broglie propose? What are the equations he formulated?

Answer 14

That particles, like electrons, could behave like waves and that the equation lamda = h/p where lamda is wavelength, h is Planck’s constant, and p is the electron’s momentum could calculate this wavelength, the other version of this is lamda = Planck’s constant / mass x velocity

Question 15

What condition is in play when diffraction is the greatest it can be?

Answer 15

When the wavelength of the particle/wave is the same/approximately the same as the gap it is passing through

Question 16

What is wave particle duality?

Answer 16

The idea that matter and radiation can sometimes be best described sometimes as particles or sometimes as waves

Question 17

What are semiconductors?

Answer 17

Materials that have been treated so that they have a low work function and react to visible light and infrared radiation. They can be found in CCDs in cameras and photovoltaic cells

Question 18

What is the equation to find the momentum of a photon?

Answer 18

Momentum of photon (p) = Planck’s Constant (h) / Wavelength (lambda)

Question 19

What is the De Broglie wavelength and when should you use it?

Answer 19

The wavelength of a particle acting as a wave, you should only use it when in an exam they say the conditions are as such

Question 20

What was proof that electrons specifically could act as waves?

Answer 20

That since they and X-rays, as predicted by De Broglie, when the electrons were travelling at about 0.1 to 1% of the speed of light, had the same wavelength, they should diffract by the same crystals. It was proved in 1927 that they did indeed