what are corpuscles
tiny particles that newton thought light was made up of
what was newtons laws of motion
that light travels in straight lines and that waves bend in the shadow of an obstacle
what was newtons theory of reflection
that reflection was due to a force that pushed particles away from the reflecting surface
what was newtons theory of refraction
he believes refraction occurred because the corpuscles travelled faster in a denser medium like glass
what did hoygen predict would happen to light when it entered a denser medium
it would slow down
why was newtons corpuscular theory of light more popular than hoygens theory
- because describing light as a stream of particles explained reflection and refraction in a way which fitted with the understanding of physics at the time
- the equipment at the time wasn’t capable of demonstrating diffraction in light
- no experimental evidence to support hoygens until young’s interference experiment
- newtons power of reputation
how did young’s double slit experiment work
Thomas young used one point source of light and placed a screen with a narrow slit and a double slit infront of it. the light would diffract the rough the narrow single slit and was then diffracted through the double slit. ensuring that this was coherent to 2 coherent light sources. the waves super posed forming a pattern of bright + dark fringes
what was fizeaus experiment
- fizeau measured the speed of light
- a beam of light was shone at a partially reflecting mirror which directed the beam between the teeth of a rotating toothed wheel towards a distant mirror about 8.6Km away
- the toothed wheel was rotated at the exact speed so that the reflected beam was blocked
- using the frequency of rotation and the number of gaps, the time taken for the light to travel to the mirror and back can be calculated
- time taken and distance travelled was used to calculate the speed of light.
what did james maxwell predict
-he predicted EM waves and their speed
- he predicted that an EM wave could exist when a change in magnetic field creates a change in electric fields which then causes another magnetic field and so on
- he predicted that there would be a spectrum of EM waves travelling at the same speeds but different frequencies
what is μ0
it relates to the magnetic flux density produced by a wire when a current flows through it
what is E0 (eplison 0)
relates electric field strength to the charge of the object producing it
who discovered radio waves
heinrich hertz
how did hertz discover radio waves
- first he produced radio waves by supplying a high p.d from an induction coil causing sparks to jump across the gap of air.
- then he used a spark gap detector made up of a loop of wire to detect radio waves
- radio waves would cause sparks between the gap in the loop of wire
- the fact that p.d was induced in the loop showed that the waves had a magnetic component
how can it be shown that radio waves have an electric component
by replacing the wire loop with a second dipole, parallel to the first
what is black body
a black body can absorb all wavelengths and emit all wavelengths of radiation
what suggestions did planck make which resolved the ultraviolet catastrophe
- radiation is emitted in quanta (which we now call photons)
- the quantum is related to a single frequency
what is the photoelectric effect
photoelectric effect happens when free electons on the surface of the metal absorb energy from light. If enough energy is absorned, the band between the metal and the electron is broken and an electron is released (photoelectrons)
what are the 5 conclusions of the photoelectric effect
- no electrons were emitted it the frequency of light was below me threshold frequency winion depended on the metal
2. photoelectrons emitted had a range ot kinetic energies from O to a max value. Max Ek increases with the frequency of radiation and isn’t eftected by intensiry of radiation.
3. photoelectric effect occurs the moment that the light is incident on the metal surface. (no time delay) 4. no metal could emit electrons when illuminated by red light - the number of photoelections emitted per second is directly proportional to the intensity of radiation.
why couldn’t the wave theory explain the photoelectric effect
- for a particular freq of light, the energy of the wave depends on its amplitude and is spread evenly ever the wavefront
- each free electron on the metal surface would gain a bit of energy from each incoming wave
- gradually, each electron would gain enough energy to be able to leave the metal.
how do you increase the radius of the lines in a diffraction pater
by increasing the wavelength of the wave
how do you increase angle of diffraction
by decreasing velocity
how are images on a scanning tunneling microscope produced
by using quantum tunneling, where electrons from the tip of the probe in a sample move across the 1nm gap (from negative to positive) creating an tunneling current
what are the 2 modes of quantum tunneling
mode 1 - constant current mode
mode 2- constant height mode
what is the constant current mode
- the height of the probe is varied in order to keep tunneling current constant
- variations in vertical positions of the probe with time are used to image the surface of a sample
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3- quantum phenomena49
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11- materials28
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6+7 forces in equilibrium + on the move18
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Waves and optics89
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8- newtons laws of motion6
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9- forces and momentum10
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10- work, energy and power10
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circular motion10
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19- thermal physics19
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18- simple harmonic motion27
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fields97
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20- gases22
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nuclear physics31
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turning points27
