Quantum Physics Flashcards
describe what would happen to an uncharged gold-leaf electroscope if its top surface were to come into contact with a positive electrode [2]
it would gain a positive charge [1] and the gold leaf would rise [1]
if a particular metal had a threshold frequency in the red part of the visible spectrum, explain what would happen to the metal if radiation was incident on its surface from the INFRARED part of the spectrum [2]
no emission [1]
infrared protons are below threshold frequency and have insufficient energy [1]
if a particular metal had a threshold frequency in the red part of the visible spectrum, explain what would happen to the metal if radiation was incident on its surface from the BLUE part of the visible spectrum [1]
emission of photoelectrons because blue photos are above threshold frequency [1]
explain why the maximum kinetic energy of photoelectrons emitted during the photoelectric effect depends on the frequency of the incident radiation [3]
- energy transferred to each electron comes from a single photon in a one-to-one interaction [1]
- energy of each photon depends on frequency (E = hf) [1]
- greater frequency results in higher energy of the photon and so the greater maximum kinetic energy of the electron [1]
the threshold wavelength is the longest wavelength that will give rise to the photoelectric effect. derive an expression for threshold wavelength in terms of threshold frequency f0
maximum wavelength that would cause photoelectric emission from the surface of the metal
state and explain the effect of quadrupling the intensity of incident radiation (keeping the frequency constant) on a metal surface emitting photoelectrons
- increased emission [1]
- number of emitted electrons per second quadruples [1]
- quadrupling the intensity results in 4x number of photons, therefore 4x the number of electrons emitted [1]
describe the photoelectric effect in terms of a gold-leaf electroscope
- the electroscope has a negative charge
- this causes the gold leaf to rise as its repelled by negative stem
- UV light is shone on metal top plate, the gold leaf falls (shows electroscope loses charge)
- electrons (now called photoelectrons) have been emitted from the top plate
What is a photon?
A quantum of electromagnetic energy
How do you calculate the energy of a photon?
E = hf
What is an electron volt?
the amount of energy gained or lost by an electron passing through 1V
how to convert from eV to J?
multiply by e (1.6 x 10^-19)
how to convert from J to eV?
divide by e (1.6 x 10^-19)
what is the threshold p.d. of an LED?
the minimum potential difference required for the LED to produce light
how can the threshold p.d. of an LED be used to find photon energy?
the energy transferred by the electrons (e x V) is equal to the energy of the photons produced (hf)
what is meant by wave-particle duality?
all matter can display both wave and particle properties
what is the key piece of evidence for wave particle duality?
when an electron beams passes through polycrystalline graphite it produces diffraction and an interference pattern
what does the de Broglie wave equation apply to?
Everything
what is the relationship between momentum and wavelength?
inversely proportional
what is the photoelectric effect?
the emission of electrons from a metal surface when illuminated with light
what is the atomic structure of a metal?
a lattice of positive ions surrounded by a sea of negative electrons
what is a photoelectron?
an electron that has been removed from a metal by absorbing a photon
what is the work function?
the minimum amount of energy needed for an electron to produce photoelectrons from a metal
what is the threshold frequency?
the minimum frequency of light needed to produce photoelectrons from a metal
what is monochromatic light?
light of 1 frequency/wavelength
