3- quantum phenomena

Question 1

what are properties of particles

Answer 1

-have mass
-have kinetic energy
- have momentum
-obey newtons laws of motion
travel in straight lines unless a force acts on them
keep their energy until they interact

Question 2

wave properties

Answer 2

-no mass
-no kinetic energy
-no momentum
-do not obey newtons laws of motion
-reflect
-refract
-diffract
-lose energy as they leave the source

Question 3

what is the photoelectric effect

Answer 3

when electromagnetic radiation is incident on a metal surface causing the EM radiation to be absorbed by electrons causing them to be emitted from the surface of the metal

Question 4

how can the photoelectric effect be demonstrated

Answer 4

electroscope

Question 5

what are electrons removed by the photoelectric effect called

Answer 5

photoelectrons

Question 6

how do we know light is quantisised/ carried in discrete packets

Answer 6

because each electron can only absorb one photon

Question 7

how does the electroscope work

Answer 7

-the electroscope is given a negative charge there4 the gold leaf is also negatively charged
-the gold leaf moves away from the anode due to repulsion
-when EM radiation is incident on the metal plate, the gold leaf will slowly fall
-this is due to the metal plate losing electrons due to the photoelectric effect there4 the electrons from the gold leaf will travel up the anode to replace the electrons lost by thermal metal plate

Question 8

what is the threshold frequency

Answer 8

the minimum frequency of incident EM radiation required for photoemission to take place

Question 9

what is the threshold wavelength

Answer 9

the longest wavelength of incident EM radiation that would remove an electron from the surface of a metal

Question 10

equation relating frequency and wavelength

Answer 10

v= f λ

v= wave speed
f= frequency
λ= wavelength

Question 11

what does the intensity of the radiation effect

Answer 11

the number of electron emitted per second by photoelectric emission

Question 12

what happens when you increase the frequency of the radiation

Answer 12

you increase the kinetic energy of the photoelectron

Question 13

what is the equation linking the amount of energy of each photon to the frequency of EM radiation

Answer 13

E= hf

E= energy of photon

or

E= hc/ λ

c= speed of light

Question 14

what is the work function (Φ ) threshold of a material

Answer 14

the minimum energy required to release a photoelectron from the surface of a metal

Question 15

photoemmison for UV light, Blue light and red light

Answer 15

UV- a lot of energy so electron leaves surface w extra energy converted to kinetic energy as it moves away
blue- lower energy than UV, electron leaves metal surface but not enough energy left over as KE
red- low energy, photoemission does not occur

Question 16

why do alkali metals have lower threshold frequency’s like visible light

Answer 16

because the attractive forces between the electrons and and the positive metal ions are relatively weak

Question 17

why do transition metals have higher threshold frequency’s

Answer 17

because attractive forces between electrons and and positive metal ions are much stronger

Question 18

what is the photoelectric equation

Answer 18

hf= Φ + Ek

Ek= kinetic energy
hf= energy of photon

Question 19

threshold frequency equation

Answer 19

Fo = Φ/ h

Question 20

what is stopping potential (Vs)

Answer 20

the potential difference required to stop photoelectric emission from occurring

Question 21

how do you each stopping potential

Answer 21

by increasing the emf of the supply until a p.d is reached at which no electrons can cross a gap

Question 22

what is the stopping potential (Vs) equations

Answer 22

Vs= w/Q =. E/Q. = Ek max/ e

e= charge of an electron

Question 23

what happens to photoelectric current when frequency is increased but intensity is kept constant

Answer 23

photoelectric current will decrease

Question 24

how do you convert joules to electron volts J- eV

Answer 24

1eV= 1.6x10^-19 J

eV to J = x1.6x10^-19
J to eV = / 1.6x10^-19

Question 25

what is intensity

Answer 25

the rate of energy transferred per unit area

Question 26

why is there a maximum kinetic energy

Answer 26

because some electrons are neared to the surface of the metal than others meaning less energy is used to remove them from the surface resulting in those photoelectrons having more Ke than those deeper in the metal

Question 27

what is photoelectric current

Answer 27

a measure of the number of photoelectrons emitted per second

Question 28

how do you calculate photoelectric current

Answer 28

number of electrons emitted. x charge on one electron

Question 29

what is the calculation for intensity

Answer 29

intensity = nhf/ tA n= number of photons t= time A= area

Question 30

how do electrons move from one energy level to another to another

Answer 30

by absorbing or emitting emitting a photon

Question 31

what is the ground state

Answer 31

the lowest energy level, where the electron is usually found as it is the most stable configuration of the atom

Question 32

what happens to energy levels when a photon is emitted by an electron

Answer 32

the electron moves from a higher energy level to a lower energy level

Question 33

what is excitation

Answer 33

when an electron absorbs a photon of energy and moves from the ground state to a higher energy level

Question 34

what is the difference between two energy levels equal to

Answer 34

a specific photon energy

Question 35

what equation relates wave length and energy difference

Answer 35

λ= hc/ E2- E1

Question 36

what is ionization

Answer 36

when an atom gains or loses an orbital electron and becomes charged

Question 37

what is ionization energy of an atom

Answer 37

the minimum energy required to remove an electron from the ground state of an atom

Question 38

what does it mean when an element fluoresces

Answer 38

it means the element absorbs photons of UV light and them emits photons of visible light

Question 39

what are fluorescent tubes

Answer 39

partially evacuated glass tubes filled with low pressure mercury vapour with a phosphor coating on the glass

Question 40

how does a line spectra occur

Answer 40

when excited atoms emit light of certain wavelengths which correspond to different colours

Question 41

what are the two types of line spectra

Answer 41

emission spectra absorption spectra

Question 42

what can the wave theory of light be used to explain

Answer 42

effects such as reflection, refraction, diffraction, polarization and interference

Question 43

what is young’s double split experiment

Answer 43

a light is passed through a slit with a width of similar side to their de brogile wavelength, this causes the wave to spread out forming a diffraction pattern

Question 44

why is graphite film ideal for electron diffraction

Answer 44

because of its crystalline structure. the gaps between atoms in the crystals act as slits, allowing the electron waves to spread out and create a diffraction pattern

Question 45

how do you increase the diameter of the ring diffraction pattern

Answer 45

by lowering the accelerating voltage

Question 46

how do you decrease the diameter of the ring diffraction pattern

Answer 46

by increasing the accelerating voltage

Question 47

what happens to the electron wavelength when you decrease the momentum

Answer 47

the wavelength will increase

Question 48

what happens to electron wavelength when you increase the speed

Answer 48

the wavelength will shorten

Question 49

what is the equation of de broglie wavelength in terms of the kinetic energy of the particle

Answer 49

λ = h / √ 2mE