AQA A level PHYSICS - Turning points

AQA A level PHYSICS - Turning qg qg qg qg qg


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1. WhatStudy online
were theat three
https://quizlet.com/_7sedu0
observations of cathode rays in a discharge
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tube and the conclusion made from each one?: 1. Tube glowed were ray
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hit glass - showed particles carried energy
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2. Rays were distorted by magnetic field - were negatively charged
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3. Cast a shadow - particles moved in straight lines
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2. What is thermionic emission?: When a metal is heated, giving the free
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elec- trons in it enough energy to escape, producing a beam of electrons
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3. Describe the arrangement of an electron gun: A metal filament is
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heated producing a beam of electrons by thermionic emission. The
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electrons are then accelerated through a high voltage towards an anode.
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Some pass through a small hole in the anode producing a thin beam.
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4. Describe and explain Thomson's method to determine the specific
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charge of an electron (fine beam tube): Glass tube containing gas at a
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low pressure with a magnetic field applied across it. Electron gun produced
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beam of electrons into the tube at right angles to the field, so they follow
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a circular path. Paths could be seen as electrons excited gas atoms causing
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them to emit photons. Magnetic force
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= centripetal force, that value of v subbed into eV=1/2mv2
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5. Why was Thomson's measured value of the specific charge of the
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electron significant compared to that of a hydrogen ion?: Thomsons
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measured value was about 1800 times larger than the hydrogen ions
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(protons). The mass of a proton is about 1800 times greater than an
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electrons, and so it was proven that the magnitudes of the charge on a
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proton and electron are equal.
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6. Describe and explain how Millikan's experiment showed the charge
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of an electron: 1. measure terminal speed of falling droplet at terminal
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speed weight = upthrust.
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show equations qg

2. rearrange to find r. r gives you m because density x volume
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3. large number of measurements multiples of 1.6... so therefore charge is
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1.6...
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7. What was Newton's theory of light? what was his main argument?:
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The 'Corpuscular theory' in which light consists of tiny particles. At the
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time, light was not known to diffract as experiments weren't accurate
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enough. It was known that particles travel in straight lines and waves
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diffracted, so light must have been made up of particles.
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8. How did Newton's theory of light explain refraction?: Newton stated
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that the corpuscles were attracted into transparent materials. Their parallel
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velocity was unchanged but their perpendicular velocity increased, so speed
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increased, so he stated that light travelled faster in denser materials
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, AQA A level PHYSICS - Turning qg qg qg qg qg


points qg


9. HowStudy
did online at https://quizlet.com/_7sedu0
Newton's theory of light explain reflection?: Newton
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stated that a force pushed the corpuscles away from surfaces. Their
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parallel velocity was unchanged but their perpendicular velocity reversed
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direction.
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10. What was Huygen's theory of light?: That light travelled as a wave. Each
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point along a wavefront was a source of secondary wavelets that travelled
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forward at the same speed as the wave. The new wavefront was a surface that
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was tangential to all of the secondary wavelets. He predicted light speed and
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wavelength would decrease in denser materials. He also predicted diffraction
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and interference. But he wrongly predicted that light was a longitudinal
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wave
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11. Give four reasons why Newton's theory of light was preferred over
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Huy- gens: Newton's reputation was stronger due to work on gravity and
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motion, no experimental evidence for diffraction or interference, no
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experimental evidence of how speed of light changes in denser material,
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fit better with understanding of physics at the time.
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12. Why was Young's doubt slit experiment significant in the
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qgdevelopment of theories of light, and why were its conclusions not qg qg qg qg qg qg qg qg qg qg

qgimmediately accepted?: - Young's double slit experiment was the first
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experimental evidence of diffraction an interference, so so proved Huygens
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theory and disproved newtons theory. Huygens theory still was not accepted
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unit years late until it was proven that the speed of light decreases in denser
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materials.
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13. Describe Fizeau's experiment for the speed of light and what value
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he got (how the equation is derived): Fizeau shone pulses of light that
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were reflected by a partially silvered mirror through a cog, and reflected back
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by a mirror at a distance away back to an observer. At low rotational speeds
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the light is transmitted through the gap and reflected back through the same
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gap, so, light os seen by the observer. As the rotational speed increases,
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there comes a point where the transmitted light passes through a gap and
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the reflected light is blocked by the adjacent gap, so cannot be seen by
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an observer. If the speed is double again, light is seen again
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as it passes through the adjacent gap. A tooth replaces a gap after 1/2nf
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seconds (n=number of teeth and f=frequency). D is the distance from the cog
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the far away mirror so 2d/2nf = 4ndf = speed of light. Fizeaus value was
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3.13x108 ms-1.
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14. How was Fizeau's experiment significant in the determination of the
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theory of light?: Fizeau used his experiment to measure the speed of light in
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water. He saw that it was slower in water, disproving Newton's theory and
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