turning points - discovery of the electron

Question 1

what happened to the glowing gas near the anode when a magnet was brought near and what did this show (

Answer 1

• it was distorted
• charged particles are responsible for the glowing gas

Question 2

how did he conclude that there must be a radiation with a charge moving from the cathode to the anode

Answer 2

• the paddle wheel turned in that direction and when a magnet was brought close it stopped turning

Question 3

why did the paddle turn

Answer 3

it had gain kinetic energy from the cathode rays

Question 4

what did JJ Thomson prove about the particles

Answer 4

• they all had the same specific charge and it did not matter what gas was in the tube
• some particles emitted for every gas (same as in thermionic emission and the photoelectric effect)
• particles were part of the substructure of particles/atoms

Question 5

how are charged particles produced in the tube (so a current can flow)

Answer 5

• high voltage means electrons are pulled of gas atoms
• ionisation by collision off electrons with atoms

-positive ions near the cathode hit the cathode and cause it to release electrons (that are accelerated towards the anode)

Question 6

give two ways light is emitted from the discharge tube

Answer 6

• near the anode: electrons excite gas atoms by collision and photons are emitted when de-excitation occurs
• near the cathode: ions and electrons (moving in opposite directions) collide with each other and re-combine to emit photons

Question 7

why does gas in the discharge tube need to be at low pressure

Answer 7

USE THE POWERPOINT TO FINISH THIS

Question 8

describe the process of thermionic emission

Answer 8

when an electric current flows through the filament, the metal is heated and some electrons gain sufficient kinetic energy to leave the metal at its surface

Question 9

why is thermionic emission is negligible when the filament current is too low

Answer 9

• temp of filament depends on the current
  -kinetic energy of electrons depends on temp of filament
  -electrons must do work to leave the metal
  -electrons have insufficient energy to leave if the current is too low

Question 10

state two conclusions that weee drawn from Thomsons experiments

Answer 10

• the specific charge of the particles was around 2000 times bigger than the hydrogen ions (this was the biggest atom they had found with the biggest specific charge ) therefore, they had found a new particle
• same particle always released that appeared in all tests which means it’s part of the substructure of an atom

(bigger specific charge could be due to a smaller mass or much greater charge)

Question 11

what did millikan conclude from his measurements

Answer 11

• the multiple readings of the charge for many oil drops, showed that the charge must be quantised in whole numbers of 1.6 x 10^-19
• therefore the electrons must be responsible for the charge on each droplet, and the charge of each electron is 1.6 x 10^-19
• the quantum of charge is 1.6 x 10 ^-19