waves Nature of light Flashcards
definition of wavelength
Distance between a point and the next point that motion is repeated m
definition of frequency
Number of waves generated moving past a point per second in hz
what is the wave front
a surface which is used to represent the points of the wave which is in phase
What is reflection
the throwing back of a wave from a surface
what is refraction?
the change in direction of a wave as it enters a new medium and changes speed
when is a diffraction the most effective
when the wavelength is similar to the slit.
Diffraction definition
diffraction, the spreading of waves around obstacles
what happens to the amplitude of a wave as it diffracts
it decreases which also means its energy decreases.
What is diffraction
the spreading out of a wave as it passes through a gap
What criteria must be met for maximum diffraction to occur
the size of the gap must be of the same magnitude as the wavelength of the wave
What happens if the gap is much smaller than the wavelength of the wave
The wave will be reflected
The diffraction grating equation
n lamba = d sinO
What does electron diffraction provide evidence for
The wave nature of electrons. It suggests that particles can demonstrate wavelike properties
Diffraction pattern produced by electrons
Concentric circles or bright and dark fringes from a central bright point
What pattern should it have if it was a particle
The electron would be unaffected by the gap and pass straight through. A single bright region would be formed.
What is the name given to the wavelength of a particle
de broglie wavelength
What two factors does the de broglie wl depend on
mass and velocity
de broglie wave length equation
lamba = h/mv ( momentum) h is Planks Constant
what can mv be replaced with in the de broglie equation?
p Momentum
What is the basic process of a pulse-echo technique
- a wave pulse is emitted
-it is transmitted and reflected at the boundary between two media - the returning wave (echo) is detected
- The speed and time taken are used to calculate the distance to the object
suggest two things that may limit the amount of information that can be obtained by a pulse echo technique
- the wavelength of the radiation
- the duration of the pulse
What are the two models that can be used to describe em radiation
Particle
wave
What model does the photoelectric effect provide evidence for
The Particle model
Outline the photo electric effect
- light is shone on a metal plate
-if the light has a high enough frequency, electrons are emitted from the metal surface - if the frequency is too low, no electrons are emitted
what are the particles of light used to explain the photoelectric effect called
Photons
How do you calculate the energy of a photon
e=hf
h is planks constant
f is the frequency of light
Explain how a photon can liberate an electron
one photon interacts with one electron and transfers all its energy to it. If this energy is greater than the metals work function, the electron will have sufficient energy to be released.
What is the threshold frequency
a metals threshold frequency is the minimum frequency that a photon requires to liberate an electron from its surface
If the intensity of light being shone on a metal increases, how does the energy of photoelectrons change
The energy remains unaffected. An increase in intensity means more photons per area and so more photoelectrons are emitted
Why are photoelectrons emitted with a range of kinetic energies
the electrons are at different depths in the metal and so require different amounts of energy to be liberated. The excess energy from a photon once an electron has been liberated is the ke of the electron
the equation for the maximum ke of a photoelectron
0.5 mv ^2 max- hf -O (work junction)
What is the conversion factor between eV and J
1 ev = 1.6x10^-19 J
What happens when electrons transition between energy levels
- if electrons move to a higher energy level, radiation must be absorbed
- if electrons move to a lower energy level, Radiation is emitted
why can only certain frequencies of radiation be absorbed by an atom to cause an electron transition?
The electrons can only exist in discrete energy levels. The energy of the photon absorbed must be the exact amount of energy required to cover the difference between two discrete energy levels.
