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The discovery of the electron

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edwinesosa's version from 2015-06-17 19:04

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what happens in a discharge tubea high voltage is applied across the terminals of of the discharge tube. the cathode is connected to the negative terminal and the anode the positive. anode becomes negatively charged and anode positive as electrons flow onto or away from them. Cathode rays ionise atoms of the gas in the tube, causing them to excite and de-excite releasing photons
what happens in thermionic emmissionheating coil heats cathode in evacuated glass tube, high PD between cathode and anode, electrons emitted from cathode and accelerated towards anode in an electron gun, some electrons pass through hole in anode forming electron beam
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how do you work out specific charge of electron (magnetic field)using a deflection tube, adjust magnetic and electric fields until theyre balanced and there's no deflection, find v by equating electric force and magnetic force equations; Now use just magnetic field - find r and use r=mv/Be to find e/m
how do you measure e/m using a fine beam tubeelectrons produced through thermionic emission are made visible due to collisions with the small amount of gas in the tube; coils are placed coaxially at either side of teh tube, allowing a magnetic field to be created perpendicular to the initial direction of the beam; the path of the beam makes a circle; the electrons have kinetic energy equal to eVa(due to potential difference at anode); rearange r=mv/Be to find v; sub the equivilant of v into 1/2mv^2=eVa and rearrange to find e/m
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how is the mass of each oil droplet calculated in milikan's experimentby measuring the terminal speed of the oil droplets with the electric field switched off; then using volume=4/3pir^3; so mass=(density)*4/3pir^3; so weight=ANS*g; weight =drag force=6pinrv; rearrange to find r; plug this back into earlier equation for mass
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