2. Quantum Phenomena Flashcards
If you shine light of a high enough _______ onto the surface of a metal, it will emit electrons.
Frequency
What is the photoelectric effect?
When electrons on the surface of a metal absorb enough energy from light to overcome bonds holding it to the metal, allowing it to be released.
Define threshold frequency.
Minimum frequency required for electrons to be released from the surface of a metal.
Does intensity of the radiation affect the maximum kinetic energy a electron has.
No, frequency does.
The number of photo-electrons emitted per second is proportional to what?
the intensity of the radiation.
What are the discrete packets of electromangentic waves Einstein suggested?
Photons
What is the h in the equation: E = hf?
Planck’s constant
A photon would transfer all its _____ to one specific electron.
energy.
If one photon collides with a free electron, the energy the electrons will gain is equal to ____
hf
Define work function.
The minimum amount of energy required to break the bonds holding the electrons to the atom and allow it to flee the metals surface.
If the energy delivered by the photon is below the work function, what happens?
No electron emission
What is the equations for threshold frequency?
frequency = work function/ planck’s constant
What is the maximum kinetic energy equal to?
hf - work function
is the kinetic energy dependent on the intensity of the radiation?
No as each electron only absorbs one photon at a time. Increasing the intensity just means more photons per second on an area, each photons have the same energy as before.
Define stopping potential.
It is the p.d needed to stop the fastest moving electron.
In an atom, where do the electrons exist?
In well-defined energy shells.
How can electrons move down energy levels?
By emitting photons.
The energy of each photon either emitted or absorbed must be equal to what?
Energy needed for the electron to transition to a different energy shell.
How many joules are there in a electronvolt?
1.60 x 10^-19J
Define the electronvolt.
The kinetic energy carried by an electron after it has been accelerated through a potential difference of 1V.
Define excitation.
Movement of an electron to a higher energy level. This is done by the electron absorbing an photon which carries an amount of energy equal to the energy difference between the two energy shells.
What does it mean if an atom becomes ionised?
An electron is removed from the atom, making the atom positively ionised.
Define ionisation energy.
Amount of energy required to completely remove an electron from an electron from the atom from the ground state.
What is the ground state?
Lowest energy level, nearest the nucleus.
How is light produced in a fluorescent tube?
Free electrons collide with electrons in mercury atoms, causing them to excite to higher energy levels. These electrons then return to their original energy levels, releasing a UV photon. The phosphorus coating on the tube absorbs photons, exciting electrons to much higher orbits. These electrons cascade down the levels, emitting visible light photons.
How is a light spectrum formed?
Light from fluorescent tubes hits prism or diffraction grating, creating a line spectrum.
What is a light spectrum?
Series of bright lines against a black background. Each line corresponds to a particular wavelength of light emitted by the source.
Why is white light described as continuous?
Contains all possible wavelengths. The colours all merge into each other - there is no gaps in the spectrum.
Does hot or cold things emit a continuous spectrum in the visible and infrared?
Hot things.
Are electrons confined to energy levels in objects producing a continuous spectrum?
No, electrons are not bound to the atom and are free.
You get _____________ when light with a continuous spectrum of energy passes through a cool gas.
Line spectrum.
At low temperature, most of the electrons in the gas atoms will be in their ________________.
Ground state.
Why are certain wavelengths missing in a continuous spectrum when it comes out the other end of a cool gas.
The electrons absorb photons with a specific energies equal to the difference between two energy levels. Photons of the corresponding wavelength cause excitation of electrons. These wavelengths are missing from the continuous spectrum.
Why is finding the line spectra useful?
Each element has its own unique line spectra like a barcode and so the element can be identified using this.
___________ and ____________ show light as a wave.
Interference and diffraction.
_____________ ________ shows light behaving as a particle.
Photoelectric Effect
What was De Broglie Suggestion?
If wave-like light showed particle properties (photons), particles like electrons should be expected to show wave-like properties.
What is the ‘mv’ in the de Broglie equation?
Mass x velocity which is the momentum.
What observation can be used to show that electrons have a wave like nature.
Electron diffraction. Diffraction patterns are observed when accelerated electrons in a vacuum tube interact with the spaces in a graphite crystal.
____________ the electron speed and the diffraction pattern squashes together towards the middle. This supports the de Broglie equation.
Increase
An electron with a ___________ mass, makes the diffraction pattern more closely packed.
Greater
