chapter 13 - quantum

Question 1

photon energy

Answer 1

E = hf
or = hc/λ

Question 2

Plancks constant (h)

Answer 2

6.63 *10^-34

Question 3

photons

Answer 3

quanta of energy of electromagnetic radiation

Question 4

how does the photon energy equation show wave and particle properties of photons

Answer 4

E = hc/λ
has wave elements due to the λ
has particular elements due to the E

Question 5

eV

Answer 5

electron volt
energy gained/ lost when an electron moves across 1v
1eV = 1.6*10^-19 J

Question 6

LED

Answer 6

an electron is transfered across a pd
gains energy (eV)
electron emits energy as a photon
eV = hf
plot eV against f
grad = h

Question 7

power of a laser

Answer 7

E = hf for one proton so
P = nhf
if n = no protons per sec

Question 8

photoelectric effect UV vs visible light

Answer 8

when high freq light is shined onto a charged plate it releases photoelectrons
when low freq eg visible light no effect

Question 9

gold leaf electroscope

Answer 9

the plate has a charge which it passes down the stem and gold leaf - so the like charges repel
when UV light is shined onto this it becomes discharged so can demonstrate the photoelectrc effect as the leaf is discharged

Question 10

hwo is the photoelectric effect evidence for wave partical duality

Answer 10

if just a wave would discharge after a lomg enough / high enough intensity so must have particles (photons)
- energy of a wave is independent of freq but prop to intensity
- if wave is incident on a surface it will keep transferring energy so over time energy will increase

Question 11

conclusions from the photo electric effect that arent explained by wave theory

Answer 11

• photo electrons only emitted above threshold freq
• no. electrons is prop to intensity
• electrons emitted have a variety of KE up to max KE
• max KE ^ with f

Question 12

photon model - photoelectric effect

Answer 12

EM waves are released as discrete packets (photons)
a photon transfers all energy to one electron
the elctron will leave the surface if it has enough energy to leave
if not enough the metal just heats

Question 13

work function energy

Answer 13

minimum amount of energy needed for one electron to be released
(depends on the metal)
⍉ = hf₀
if f>= f₀ electron is released
if f < f₀ just heats up

Question 14

electron KE eq

Answer 14

KE = hf - ⍉ = h(f - f₀)
E = KE + ⍉

Question 15

finding max KE of emitted electrons

Answer 15

Vs = stopping voltage - voltag eat which electrons are attrcated back to previous plate - dont reach other side
eVs = max KE (I = 0)
graoh of KE againts f
KE = hf - hf₀

Question 16

de broglie λ

Answer 16

E = hc/λ = mc^2
λ = h/mv = h/p
shows the λ of an electron

Question 17

double slit experiment

Answer 17

matter fired through a double slit should give the same pattern as the slits (||) but whenelectrons are fired through a double slit an interference pattern is produced (|||||)
but when the slit is observed they give the exceoted || pattern
shows wave particle duality

Question 18

electron gun

Answer 18

• filament is heated
• electrons gain KE
• some escape through thermonic emission
• high pd accelerates towards anode
• gains high KE
• pass through hole in anode (makes electron beam)

Question 19

linear accelerator

Answer 19

• series of electrodes
• accelerates electrons several times
  λ = h/ root(2meV)
  λ ∝1/ root(v)

Question 20

electron diffraction

Answer 20

in an evacuated tube - an electron gun is fired towards a graphite target and onto a phosphor screen
creates rings of maxima

Question 21

diffraction rings

Answer 21

the grating is graphite so diffraction is in all directions and makes a ring
nλ = d sinθ
if v increases rings get smaller/ closer
d = h/mvsinθ = spacing between atoms

Question 22

wave particle duality - electrons

Answer 22

λ = h/mv
electrons act like a wave - have wavlength, create interference patterns (go through difraction)
act like a particel - have mass and charge - are accelertated by electric field, deflected by magnetic field

Question 23

PHOTO ELECTRIC EFFECT

Answer 23

• photon has energy (E = hf)
• one to one relationship with electrons
• if energy of the photon is > work function of the metal an electron is released
• energy transferred from photon (hf ) = work function + KE max
• if energy is less the metal heats it - no electron is released
• intensity changes no. photons and no. photoelectrons (if f> threshold freq) but doesn’t effect KE max