chapter 7

Question 1

what is the photoelectric effect?

Answer 1

if you shine light of a high enough frequency onto the surface of a metal, it will emit electrons. For most metals, this frequency falls in the UV range.

1) free electrons on the surface of the metal absorb energy from the light, making them vibrate
2) if an electron absorbs enough energy, the bonds holding it to the metal break and the electron is released.
3) this is called the photoelectric effect and the electrons emitted are called photoelectrons

Question 2

what are the 3 conclusions from the photoelectric effect?

Answer 2

1) for a given metal, no photoelectrons are emitted if the radiation has a frequency below a certain value called the threshold frequency
2) the photoelectrons are emitted with a variety of kinetic energies ranging from 0 to some max value. This value of the max ke increases with the f of the radiation, and is unaffected by the intensity of the radiation
3) the no. of photoelectrons emitted per second is proportional to the intensity of the radiation

Question 3

what is a quantum of EM radiation

Answer 3

a photon

Question 4

what can be suggested about EM waves?

Answer 4

that they can only be released in discrete packets, called quanta. a single packet of EM radiation is called quantum

Question 5

what can only exist is discrete packets?

Answer 5

Em waves, these wave-packets are called photons

Question 6

what is the energy carried by a photon=

Answer 6

h x frequency = hc/wavelength

where h= planck’s constant, 6.63 x 10^-34 Js
f=frequency
c- speed of light in a vacuum= 3 x 10^8 m/s

Question 7

the higher the frequency of the of the em radaiation

Answer 7

the more energy its photons carry

Question 8

a photon acts as what

Answer 8

a particle, and will either transfer all or none of its energy when interacting with another particle like an electron

Question 9

what are the two things understood according to the photon model?

Answer 9

1- when light hits its surface, the metal is bombarded by photons
2- if one of these photons collides with a free electron, the electron will gain energy equal to hf

Question 10

what is the work function energy?

Answer 10

before an electron can leave the surface of the metal, it needs enough energy to break the bonds holding it there. this energy is called the work function energy and its value depends on the metal

Question 11

how can electrons in an atom only exist

Answer 11

only exist in certain well-defined energy levels, each level is given a number, with n=1 representing the ground state

Question 12

how can electrons move down an energy level?

Answer 12

by emitting a photon

Question 13

since these transitions are between definite energy levels,

Answer 13

the energy of each photon emitted can only take a certain allowed value

Question 14

what is the energy carried by each photon equal to

Answer 14

to the difference in energies between two levels

Question 15

what happens if u heat a gas to a high temp

Answer 15

many of it’s electrons move to higher energy levels, as they fall back to the ground state, these electrons emit energy as photons

Question 16

what happens if u split the light from a hot gas with a prism or a diffraction grating

Answer 16

you get a line spectrum. A line spectrum is seen as a series of bright lines against a black background. Each line on the spectrum corresponds to a particular wavelength of light emitted by the source. Since only certain photon energies are allowed, you only see the corresponding wavelengths.

Question 17

what happens when you shine white light through a cool gas

Answer 17

it gives an absorption spectrum

Question 18

what is the spectrum of white light

Answer 18

continuous

Question 19

what happens if u split the light up with a prism

Answer 19

the colours all merge into each other- there aren’t any gaps in the spectrum

Question 20

what do hot things emit

Answer 20

a continuous spectrum in the visible and infrared

Question 21

what path will a photon take

Answer 21

all of the possible paths to the detector in one go

Question 22

how can you keep track of a photon

Answer 22

using phasors

Question 23

what can you use phasors to show

Answer 23

how light or dark a certain spot on a screen will be, u can use phasors to tell you how probable it is that a quantum will arrive there

Question 24

frequency of the phasor’s rotation=

Answer 24

photon’s energy/ plank’s constant

Question 25

probability =

Answer 25

(resultant phasor)^2