Cathode Ray Flashcards
Charged particles responsible for making the gas in the cathode ray tube conducting are produced when:
- electrons pulled out of the gas atoms making them positive ions (ionisation) - conduction to the negative electrons and the positive ions
Gas emits light because:
- ions and electrons collide and recombine to emit photon - electrons excite gas atoms by collision and emit photon when de-excite
Low pressure gas needed so:
- electrons in the tube need to be widely spaced otherwise they’d be stopped by the gas atoms and lose kinetic energy preventing excitation from occurring
Different types of gas in tube =
same charge, different mass for positive ions therefore different specific charge
Why evacuated tube
to prevent electron al collision with atoms which would reduce speed and kinetic energy of electrons
Glowing gas as
electrons present, accelerated by electric field, excitation of gas atoms, photons emitted on return to lower energy
What order of voltage is used in the discharge tubes
10^3
What created the electric field
pd applied between two electrodes
Explain the entire process (10):
1) Electric field created by pd + electrodes 2) This ionises gas atoms making them +ve 3) They’re accelerated by the pd towards the cathode 4) Upon colliding with anode, electrons knocked off 5) Which are accelerated to anode and collide+ionise gas atoms 6) Some +ve ions + electrons recombine near cathode 7) This causes photon emission and –ve glowing gas near cathode 8) Electrons not recombining attracted to anode and excite gas atoms 9) De-excitation emits photons causing +ve column of gas 10) Glowing gas = emission of cathode rays (electrons) towards anode
How did placing a magnetic field near the tube affect the paddle wheel and what is the significance
stopped it from rotating by deflecting the cathode rays away from it showing that charged particles move through the gas when it conducts electricity – direction of deflection showed they were –vely charged.
Changing the type of gas in the tube changes
the colour of emitted light
Thomson demonstrated that these cathode rays
have energy, momentum, mass, negative charge, specific charge > H+ ions, same properties regardless of gas in tube
Diagram
Explain why the glowing gas in a discharge tube is distorted when a magnet outisde the tube is placed near the glowing gas.
Because the force of the magnetic field deflects the cathode rays (which are negatively charged electrons) causing different gas atoms to be excited/ionised meaning the UV rays are being emitted at a different position in the tube so the glowing gas is distorted
Must mention charge
Explain why the negative particles in a discharge tube are identical, regardless of the gas in the tube
Because they are fundamental subatomic particles (electrons) which are part of all atoms of all gases. This means whatever gas is used, it’s atoms will be ionised by the electric field and some of these particles will be pulled off - the characteristics of these electrons are unaffected by the element they are a part of
