Quanta Flashcards
What does quantum mechanics explain?
experimental observations that can not be explained by classical physics
What experimental observations can quantum mechanics explain?
- blackbody radiation
- photoelectric effect
- emission and absorption spectra
- atomic structure
- electron diffraction
What is a black body?
a surface that absorbs all wavelengths of electromagnetic radiation
What is blackbody radiation?
the continuous spectrum of radiation that a black body emits
What does the amount of black-body radiation emitted at any frequency depend on?
only temperature
What is specific intensity a measure of?
the radiation emitted by a body
How can energy be emitted or absorbed?
in discreet packets of energy called quanta
What are the results of the photoelectric effect?
- the non-emission of electrons with very bright but low frequency radiation on a metal surface
- the increase in the speed of the emitted electron with frequency but not with intensity, increasing intensity only increases the number of electrons
What equation is the energy of a photon given by?
E=hf
What is wave-particle duality?
the phenomenon that describes the fact that electrons can act as both particles and waves
What is the apparent wave-like behaviour of a particle related to?
its momentum
What is true about an electron in quantum mechanics?
it does not have an exact position
What is quantum mechanics?
the ability to calculate probabilities but not make specific, definite predictions
What does the double-slit experiment demonstrate?
that light displays wave-like properties
What is the result of the double-slit experiment using photons?
it could be concluded that the single-particle must somehow pass through both slits
What is the result of the double-slit experiment?
we can conclude that the wave and particle properties can’t be measured at the same time
Conclusions of the double-slit experiment?
- we cannot predict the exact path that either an electron or photon will follow
- we cannot make a direct measurement of the particles locations as this will interfere with the outcome of the experiment
- we can predict the probability the electron or photon has of landing at a particular point on the screen
What can be said about the maxima of waves?
this is where there is a high probability of many electrons/photons arriving thus we see a bright patch
What does Heisenberg’s Principle Uncertainty state?
The uncertainty principle says that we cannot measure the position (x) and the momentum (p) of a particle with absolute precision.
What are the other quantities that can be used to demonstrate Heisenberg’s uncertainty?
energy and time
What is quantum tunnelling?
A quantum particle can exist in a position that, according to classical physics, it has insufficient energy to occupy
What are cosmic rays?
high energy particles arriving at the earth which have originated elsewhere
Where do cosmic rays come from?
- the lowest energy cosmic rays come from the sun
* the intermediate ones come from elsewhere in the milky way and are often associated with supernovae
When does a cosmic air shower happen?
when cosmic rays reach earth they combine with particles in the Earth’s atmosphere thus resulting in cosmic air
What is solar wind?
a constant stream of particles emitted from the sun
What are solar flares?
explosive releases of energy that radiate over virtually the entire EM spectrum
What does the Earth’s magnetic field protect it from?
solar wind
What is the cavity dominated by the Earth’s magnetic field called?
the magnetosphere
What equation gives the force acting on a charge through a magnetic field?
F=qvB
Why does a particle have a helical motion in a magnetic field?
The perpendicular component provides the central force, which produces uniform circular motion
The component parallel to the magnetic field does not cause the charge to experience a magnetic force so it continues to move with constant velocity in that direction
Under what conditions would a charge in a magnetic field have a helical path?
if the charge moves at an angle to the magnetic field
Explain why an ion follows a semi-circular path
it has a central force acting on it
Why do charged particles approaching earth in the same direction not cause an aurora above the equator?
the particles never reach the atmosphere above the equator
In what terms can quantum particles be talked about?
in terms of probabilities and not certainties
If the time taken for an event is not known precisely then how will this affect the uncertainty in the energy associated with the event?
the uncertainty in energy will be low
