Flashcards
Section 2: Electromagnetic Radiation and Quantum Phenomena
Cards in this deck (24)
- 1What is the photoelectric effect?The emission of electrons from a metal surface when the surface is illuminated by light of a frequency greater than the threshold frequency
- 2Threshold FrequencyThe minimum frequency of light needed to cause photoelectric emission
- 3What happens if the incident light is below the threshold frequency?No electrons are emitted
- 4What affects the threshold frequency?The material of the surface e.g. type of metal. The intensity of the light does not affect it!
- 5Why do emitted electrons vary in KE up to a max?Vary in KE as takes some energy to reach surface. Max KE when any excess energy from photon transferred all to the KE of electron
- 6Above the threshold frequency, what happens if you increase the intensity of the incident light? (What does it not do?)Increased emission of electrons per second BUT it DOES NOT increase the KE of the electrons as they can only absorb one photon at a time)
- 7Above the threshold frequency...What does increasing the frequency of the incident light do?Increases the max KE of the emitted electrons
- 8Equation for max KE of photoelectronsMax KE= hf- work function
- 9How would the photoelectric effect be explained by wave theory?It Cant- According to Wave theory: For a particular frequency of light the energy carried is proportional to the intensity and is spread out evenly over the wavefront meaning each electron gains a bit of energy. Therefore increasing intensity and prolonged exposure would result in photo emission. also increasing intensity should increase KE)
- 10Equation for Stopping PotentialeVs = KE max
(V=E/Q)
e= charge on the electron
Vs= stopping potential - 11What energy level is ground state?n=1
- 12When electrons move down energy levels what happens?A photon of energy equivalent to the energy gap is emitted
- 13Proof for discrete energy levels in an atomSpectrum have distinct lines therefore only photons of distinct energies emitted therefore discrete energy levels
- 14What does the energy of each energy level in an atom representThe energy needed to completely remove an electron from that level
- 15What is the ionisation energy of an atomThe energy needed to completely remove an electron from the ground state (n=1)
- 16How does a fluorescent tube work?Filled with mercury vapour with a inner coating. Electrons ionise some mercury atoms. Flow of electrons created exciting other mercury atoms. When they de-excite they emit ultraviolet photons. UV absorbed by atoms in coating causing excitation. They de-excite in steps editing visible photons.
- 17What emits a continuous spectrum?Hot things (in the visible and infrared parts)
Continuous as electrons are not bound in energy levels - 18When do you get a line absorption spectrum and what does it look like?When a continuous spectrum passes through a cool gas. Dark lines appear where energy has been absorbed.
- 19What does an emission spectra look like for a particular gas?Dark and then bright lines where photons are emitted
- 20Evidence that light behaves as a waveDiffraction patterns and Interference patterns
- 21Evidence that light behaves as a particleThe photoelectric effect
- 22De Broglie equation/\ = h/mv
- 23Evidence for particle nature of ElectronsElectron beam can be bent by charged objects
- 24Evidence for wave nature of ElectronsElectron Diffraction: diffraction patterns observed when accelerated electrons interact with spaces in graphite crystal.
--> increasing speed decreases wavelength i.e. circles squash together towards centre
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- The photoelectric effect, energy levels, photon emission, absorption spectra, wave-particle duality
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- Francesca Wittmann
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