Cathode Rays Flashcards
(14 cards)
1
Q
what is an electrode?
A
- an electrode is a conductor through which electricity passes
2
Q
what is the cathode?
A
- negatively charged electrode
3
Q
what is the anode?
A
- positively charged electrode
4
Q
describe the discharge tube
A
- glass chambers containing a low pressure gas
- with an anode at one end and a cathode at the other end
- connected to a high voltage supply
5
Q
what are cathode rays?
A
- beam of negatively charged particles ( electrons ) in motion
6
Q
why were cathode rays found to be negatively charged?
A
- when a magnetic field was applied to the glass tube, the path of cathode rays was deflected
7
Q
how does the discharge tube conduct?
A
- heating the cathode
- electron acceleration
- electron - gas collisions
- ionisation and creation of free electrons
- light emission
8
Q
how does thermionic emission work?
A
- when the voltage supply is turned on, the cathode heats up
- this gives energy to the electrons to overcome the work function
- these free electrons are emitted from the cathode
9
Q
explain what happens during the electron collisions with gas atoms
A
- as the electrons travel through the tube, they collide with gas atoms inside the tube
- these collisions can ionise the gas atoms or excite the atoms
10
Q
explain what happens to the ionisation and free electrons in the tube?
A
- ionisation process creates positive ions and free electrons
- these help to conduct electricity, allowing a current to flow through tube
11
Q
how does light emission and glow occur?
A
- excited gas atoms eventually de-excite by returning to their ground state, releasing energy in form of visible light
- colour of the glow depends on the gas used
12
Q
how do cathode ray tubes work?
A
- similar principle to discharge tubes
- the use of acceleration of electrons towards the anode allows a beam of electrons to be fired
- anode consists of a small ring
13
Q
what is the work done on an electron in a cathode ray tube?
A
eV = mv^2 / 2
14
Q
what are the main differences between a CRT and a discharge tube?
A
- CRTs contain no gas, discharge tubes contain low pressure gas
- electrons do not undergo ionisation in CRTs
- thermionic emission are main source of electrons for CRTS
