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Descrição
FlashCards por Michael Priest, atualizado more than 1 year ago
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Criado por Michael Priest
mais de 9 anos atrás
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| Questão | Responda |
| What are cathode rays? | Electrons |
| What is thermionic emission? | Electrons emitted from a heated cathode |
| How much energy does an electron gain when accelerated by a p.d. V | The product of the electron's charge and the accelerating p.d. (eV) |
| A fine beam tube is used to confine electrons to a circular path. Why do the electrons not spiral inwards? | Magnetic force is perpendicular to the velocity of the electron, so does no work on it in the direction of the centripetal force |
| Give the 3 factors that affect the frictional force in Stokes' Law | viscosity speed radius (of droplet) |
| What did Milikan's oil droplet experiment discover? | The charge of the electron |
| Describe Newton's ideas about light | Light is a particle Travels faster in denser materials (attracted to them) Couldn't explain interference |
| Describe Huygen's ideas about light | Light is a wave Light is longitudinal Light travels slower in more dense materials Polarisation can't be explained |
| What is wave-particle duality? | Waves can behave like particles and particles can behave like waves in particular situations |
| How did Einstein explain the photoelectric effect? | Light is a particle (called a photon), with energy E = hf Photons interact with electrons in 1:1 interactions Electrons are only liberated when the photon has energy greater than the work function |
| Describe one experiment where particles behave like waves | Electron diffraction through a thin slice of crystal Electrons produce an interference pattern (or electron microscope description) |
| Describe one experiment where light behaves like a particle | Photoelectric effect, light above a certain frequency liberates electrons from a metal surface |
| Describe one experiment where light behaves like a wave | Young's double slit experiment Two coherent light sources interfere and produce an interference pattern |
| Describe one experiment where electrons behave like particles | Deflection by electric or magnetic fields |
| Describe the functions of the 3 lenses in a Transmission Electron Microscope | Condenser Lens - controls beam width Objective Lens - magnifies Magnifier Lens - Magnifies and focusses |
| Describe how a Scanning Tunnelling Microscope works | Electrons have a wave-like nature Small probability that an electron can tunnel across the gap Tunnelling current is inversely proportional to the separation Distance controlled to give an image of the surface. Transfer is from – to + only |
| Describe an electromagnetic wave | Oscillating electric and magnetic fields Electric component and magnetic component are in phase and at 90 degrees to each other and to the direction of propagation |
| How does this equation show that light is an electromagnetic wave? | Values of permittivity and permeability of free space determined experimentally. Solving the equation gives c = 300 000 000 m/s which is the speed of light |
| Explain how a radio wave induces an alternating EMF in a metal loop | Radio wave has an electric component that oscillates parallel to the electrons in the loop The electric field is alternating so the EMF is alternating too |
| What was the Michelson-Morley interferometer experiment designed to prove? | The existence of the aether |
| In the Michelson-Morley experiment what caused the fringe pattern? | The distance travelled by the two light beams meant that a phase difference existed Bright fringes when constructive interference occurred and vice-versa |
| In the Michelson-Morley experiment a fringe shift was expected. Explain why. | The motion of the Earth through the aether was supposed to affect the speed of light. The rotation of the apparatus meant that the light beams would be swapped causing the fringe shift due to the difference in the speed of light. |
| What are the 2 postulates for Einstein's theory of special relativity? | 1. Physical laws have the same form in all inertial reference frames 2. The speed of light in free space is invariant |
| What is an inertial reference frame? | A frame of reference that moves at constant velocity with no acceleration |
| How does time dilation account for the detection of muons on mountain-tops? | Muons travel close to the speed of light so experience time dilation, they exist for longer than their half-life in a stationary reference frame |
| Length contraction affects muons as they travel at relativistic speeds. Explain how. | The distance they travel is contracted from the muons' point of view. From a stationary reference frame, their half life is longer. |
| What quantity does this equation represent? | The kinetic energy of a relativistic particle |
| What quantity does this equation represent? | The relativistic mass of a particle |
| What does this equation represent? | The total relativistic energy (both rest mass energy and kinetic energy) of a particle |
| It is impossible for a particle to travel at the speed of light. Explain why. | As v approaches c, the mass of a particle increases and tends towards infinity, which is impossible |
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