quantum physics

Question 1

two theories of nature of light in 17th century

Answer 1

corpuscular theory (supported by newton) as it being a tiny stream of particles travelling at high speeds in straight lines.
wave theory

Question 2

differences between corpuscular theory and wave theory

Answer 2

both explained refraction and reflection.
waves needed a transmitting medium that was undetected.
interference and diffraction began to explain wave.
fluctuating electric and magnetic fields suggested, which didn’t need a transmitter

Question 3

photoelectric effect

Answer 3

emission of electrons from a metal surface when light shines on it. electrons are able to escape because repelled by other negative charge once liberated

Question 4

the photoelectric effect’s impact on wave theory

Answer 4

would expect uniform distribution of the whole area the light hit, but:
only observed when at a certain light frequency threshold that is dependant on the metal regardless of intensity.
emission instantaneous even with faint light.
maximum speed of electrons only dependant on frequency.
only explains number of electrons emitted per time is proportional to intensity.

Question 5

Einstein’s photoelectric equation

Answer 5

extension of quanta theory (E=hf [h plank’s constant]).
assumes electromagnetic radiation emitted and absorbed as quanta called PHOTONS. where they can give all energy to an electron and cease to exist, but only at a certain energy level, giving the THRESHOLD. extra energy becomes kinetic
hf=Φ (work function hf0) + Emax

Question 6

energy threshold radiation (hf0)

Answer 6

energy needed to release lest tightly bound electrons

Question 7

energy of radiation (hf)

Answer 7

energy to release electron (variant on electron shell) +kinetic energy
special case it = energy release least tightly bound electron (hf0) + Emax

Question 8

within Einstein’s theory, greater intensity

Answer 8

allows more photons to arrive per second and area, but not change their energies

Question 9

experiment to test Einstein’s photoelectric model

Answer 9

Milikan’s experiment.
monochromatic light from a spectrometers enters vacuum chamber and falls on electrode of the test metal, photoelectrons emitted collected by a second electrode with a sensitive ammeter
the stopping potential V was found for different frequencies

Question 10

stopping potential V in Milikan’s experiement

Answer 10

has to be applied to prevent most energetic photoelectrons causing current flow

Question 11

effect of frequency on IV graph

Answer 11

max current is decreased and stopping potential V stretched left/right

Question 12

effect of intensity on IV graph

Answer 12

maximum current increased

Question 13

why hf=hf0+eV

Answer 13

because the most energetic electrons will just transfer the kinetic energy to Ep as the fail to reach second electrode

Question 14

wavelength=

Answer 14

c/f

Question 15

workfunction of a metal=

Answer 15

hf0

Question 16

decay constant

Answer 16

the prob that a nucleus will decay in a unit time