7301642
Description
Flashcards by Francesca Wittmann, updated more than 1 year ago
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Created by Francesca Wittmann
almost 8 years ago
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| Question | Answer |
| What 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 |
| Threshold Frequency | The minimum frequency of light needed to cause photoelectric emission |
| What happens if the incident light is below the threshold frequency? | No electrons are emitted |
| What affects the threshold frequency? | The material of the surface e.g. type of metal. The intensity of the light does not affect it! |
| Why 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 |
| Above 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) |
| Above the threshold frequency...What does increasing the frequency of the incident light do? | Increases the max KE of the emitted electrons |
| Equation for max KE of photoelectrons | Max KE= hf- work function |
| How 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) |
| Equation for Stopping Potential | eVs = KE max (V=E/Q) e= charge on the electron Vs= stopping potential |
| What energy level is ground state? | n=1 |
| When electrons move down energy levels what happens? | A photon of energy equivalent to the energy gap is emitted |
| Proof for discrete energy levels in an atom | Spectrum have distinct lines therefore only photons of distinct energies emitted therefore discrete energy levels |
| What does the energy of each energy level in an atom represent | The energy needed to completely remove an electron from that level |
| What is the ionisation energy of an atom | The energy needed to completely remove an electron from the ground state (n=1) |
| How 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. |
| What emits a continuous spectrum? | Hot things (in the visible and infrared parts) Continuous as electrons are not bound in energy levels |
| When 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. |
| What does an emission spectra look like for a particular gas? | Dark and then bright lines where photons are emitted |
| Evidence that light behaves as a wave | Diffraction patterns and Interference patterns |
| Evidence that light behaves as a particle | The photoelectric effect |
| De Broglie equation | /\ = h/mv |
| Evidence for particle nature of Electrons | Electron beam can be bent by charged objects |
| Evidence for wave nature of Electrons | Electron 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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