quantum Flashcards
explain why current in photocell only if frequency is above a certain value(3)
- energy photon (1)
- greater than work function –so electrons emitted
effect on current of increased intensity radiation (2)
- current greater (more electrons emitted per second)
- increased intensity = more photons incident per second
work function
energy required to remove electron
minimum energy required to remove an electron from metal surface
comparing x rays and UV - what can be said ?
same element, photoelectrons emitted using x rays have greater max energy
when light incident on metal surface photo cell increasing intensity of illumination at surface leads to increase
in current through photocell
why emitted electrons have range kinetic energies up to a maximum
energy of photon is constant / fixed OR energy given to electron is fixed
energy required for electron to leave / escape / emit from the surface / metal
OR electron has to overcome work function
maximum kinetic energy is the energy of photon minus the work function
deeper electrons require energy to get to the surface OR have less Ek than surface electrons
effect of decreasing frequency of incident radiation while keeping intensity constant on emitted electrons (2)
-decrease energy photons
-decrease maximum kinetic energy electrons
-
effect on emitted electrons double intensity + freq constant (2)
- increase photons - increase in emitted electrons
- double number electrons emitted per second
why emitted electrons have range of ke to max 4
photons have energy dependent on frequency OR energy of photons constant
one to one interaction between photon and electron
Max KE = photon energy – work function in words or symbols
more energy required to remove deeper electrons
what must happen to validate new scientific theory (2)
theory makes predictions tested by repeatable/checked by other
scientists/peer reviewed (experiments) OR new evidence that is repeatable/
checked by other scientists/peer reviewed
why no photoelectric observed when potassium surface given positive charge (2)
surface attracts negative electron back to positive surface
photons have insufficient energy/energy required increased
explain why ke emitted has max value
hf is energy available / recieved from photons
energy required to remove electron varies
unit for work function
joules
why if freq below certain value electrons not emitted (2)
- work function minimum energy to release electron
- below certain frequency energy PHOTON less than work function
when talking about freq/energy being less than work function always say
photons as well as electrons
when do E= hf its
in joules already
energy = 9.9x10-19 and light energy incident on each square mm of surface rate of 3x10-10 Js-1
number of photons per second = 3.0 × 10–10/9.9 × 10–19 (1)
number of photons per second = 3.0 × 108 (1)
time delay in liberating electron doesn’t occur - what happened with new evidence
light travels in quanta / photon
old theory rejected
state what is meant by threshold frequency
below a certain frequency (called the threshold frequency) no electrons emitted (1)
or minimum frequency for electrons to overcome work function
always say in frequency questions
ENERGY PHOTON DEPENDS ON FREQUENCY
why no photoelectric effect below threshold freq
(light travels as photons) energy of a photon depends on
frequency (1)
below threshold frequency (photon) does not have enough
energy to liberate an electron (1)
assumption in increase intensity increases current
one photon liberates one electrons - more photons incident per second
2 points why a light causes photoelectric
high frequency above threshold
for excitation say
up
ionisation
electron removed from atom
describe what happens in an atom when line spectra produced (3)
- electrons move(or excited) from one energy level(or orbit) to another (1)
- emitting or absorbing a definite frequency / wavelength / colour (1)
- photon energy(of electromagnetic radiation) (1)
how are energy levels useful in explaining spectra (3)
- only certain energies [or energy changes] allowed (1)
a line [or photon] corresponds to transition between levels (1)
each transition [or energy change]
corresponds to a definite wavelength [or frequency] (1)
for diffraction allowed size be within
same order magnitude (power of 10)
piece of evidence for particle like properties
deflection in magnetic fields
misconception on work function with electrons in metal
all electrons have same work function just deeper down require more WORK to reach surface and escape
always say in electron level negative explanation
WORK DONE to excite electrons
must result in energy being emitted from atom =
relaxation
when talking about photon absorption to move to higher level
ALL ENERGY ABSORBED IN 1TO1 INTERACTION
electron can only trasnfer
part of its energy - so will move off with excess kinetic energy
if question says same nucleon number in long answer question then always say
same number protons and neutrons
what to say for diff maximum kinetic energy’s
energy required to liberate electrons varies (not work function!)
if work function mentioned in any question even if it seems like don’t mention it what do you do
define it - minimum energy for electron to be liberated
when time delay doesn’t occur in photoelectric what does this prove
light travels as photons in discrete packets 1to1
n. photons arriving per second=
rate / photon energy
what is ke of electron further below the surface less than
hf - work function
what will ke of emitted photons never be greater than
hf - work function
how is validated evidence formed / what is it?
experiment/observation needs to be performed (to test a theory) (1) the results of (the experiment) need to be proved/repeatable/replicated/
confirmed (1)
old theory is used to make what
predictions - then tested
what is mercury vapour at low pressure
conducting
ionisation energy
energy on level of ground state
what’s ionisation
when an atom loses an orbiting electron (and becomes charged) (1)
what happens to electrons in higher energy levels after a lower energy level electron is ionised
the orbiting electrons fall down (1)
to fill the vacancy in the lower levels (1) various routes down are possible (1) photons emitted (1)
taking away energy (1)
in ionisation don’t say emitted say to
leave atom
3 marker comparing ionisation and excitation for 1st say
in both electron receives exactly right amount of energy
why can only photons of specific freq cause excitation in an atom
electrons occupy discrete energy levels
and need to absorb an exact amount of/enough energy to move to a higher level photons need to have certain frequency to provide this energy or e = hf
energy required is the same for a particular atom or have different energy levels all energy of photon absorbed
in 1 to 1 interaction or clear a/the photon and an/the electrons
for line emission always say
how energy = wavelength equation and DIFF WAVELENGTHS PRODUCED ( as it is a spectrum)
