2617817
Description
Flashcards by kerryrandfield, updated more than 1 year ago
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Created by kerryrandfield
about 9 years ago
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| Question | Answer |
| Constructive interference | when two waves meet in phase, so amplitudes add |
| Destructive interference | when two waves meet out of phase, so they cancel eachother out |
| wavelength of RED LIGHT | (roughly) 650nm |
| wavelength of GREEN LIGHT | (roughly) 540nm |
| wavelength of BLUE LIGHT | (roughly) 480nm |
| comparing spectra from prisms and gratings | PRISM ~ one spectrum ~ bright ~ red deviated least, violet most GRATING ~many spectra ~ less intense ~ red deviated most, violet least |
| Photoelectric effect | when metals are exposed to high-frequency electromagnetic radiation ( eg UV ), electrons are ejected from their surface |
| Threshold frequency | the minimum frequency of electromagnetic radiation required in order to eject electrons from a particular metal |
| Point Source | If a point source irradiates light uniformly in all directions and there is no absorption, then irradiance decreases in proportion to the square of the distance from the object |
| what does LASER stand for? | Light Ampliication by Stimulated Emission of Radiation |
| Emission of light (photons) | light is emitted with electrons in an excited state drop to a lower energy level |
| Absorption of light (photons) | the photon energy s absorbed and the electron will jump to a higher energy level (if the photon's energy is an exact match for the difference in energy between levels) |
| Lasers | work by stimulating the emission of identical photons light is monochromatic, coherent, parallel and has very high irradiance note: LASER IS NOT A POINT SOURCE |
| n-type semiconductor | ~ majority of free charge carriers are negative (electrons) ~ electrically neutral (~usually silicon doped with arsenic) |
| p-type semiconductor | ~ majority of free charge carriers are positive (holes) ~ electrically neutral (~ usually silicon doped with indium) |
| p-n junction | p-type and n-type semiconductors next to each other. some electrons drift from n-type to fill holes in p-type. This forms a DEPLETION LAYER - depleted of charge carriers so is an insulator |
| p-n junction in forward bias | A very small voltage is needed to overcome depletion layer ( 0.7V ) Electrons flow into depletion layer then through holes in p-type Depletion layer is reduced Diode conducts electricity |
| p-n junction in reverse bias | electrons in n-type are pulled away +ve holes in p-type are pulled away by -ve depletion layer widens Diode does not conduct (until 'breakdown voltage' is reached) |
| L.E.D. | when LED conducts, electrons combine with holes to give out energy as photons of light |
| Photodiode | When a photon of light enters the depletion layer, its energy can be absorbed and an electron-hole pair created |
| Photodiode in photovoltaic mode | there is a zero bias voltage photodiode acts as a solar cell Electron-hole pairs create voltage or e.m.f. |
| Photodiode in photoconductive mode | photodiode is connected in reverse bias photons shining on the depletion layer create electron-hole pairs The free charge carriers lower the resistance and allow a small current Acts as an LDR |
| what does MOSFET stand for? | Metal Oxide Semiconductor Field Effect Transistor |
| How does a MOSFET work? | an electric field is set up between gate and substrate electrons, which draws up electrons A narrow channel of negative charge carriers is created between source and drain, allowing charge to flow |
| Findings of alpha paticle - gold experiment | ~ most particles passed straight through ~ some were deflected through large angles ~ very very few bounced back |
| conclusions of alpha particle - gold experiment | ~ most of the atom must be empty space ~ most of the mass and positive charge are concentrated in a very small area ~ the mass is very large compared to an alpha particle |
| Spontaneous Fission | a large, unstable nucleus splitting into two daughter products and releasing energy |
| Induced Fission | large nucleus absorbs a neutron, becoming unstable and splits into two daughter products, releasing energy |
| Nuclear fusion | The joining of two nuclei to form a nucleus of larger mass number, releasing energy |
| why is energy released in fission and fusion? | mass of reactants is greater than mass of products / there is a mass defect |
| Average annual effective dose of radiation | 2 mSv |
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