An Electron Gun
Electron Gun Process:
- An electric current (6V) is supplied to the filament (the coil of metal) to heat the cathode (negative electrode), giving energy to it's electrons. These start to heat up and vibrate.
- Electrons then 'boil off' and escape the cathode. This process is called thermionic emission.
- The negatively charged electrons are attracted to the anode, and accelerate towards it.
- The anode channels the electrons and concentrates them into an electron beam.
- The beam then fires past electrically charged parallel metal plates that deflect the electrons and bend the beam, reflecting them between the plates.
- The beams have so much kinetic energy due to the concentration and speed of the fired electrons, they make a fluorescent screen glow and show the path of the beam.
Changing the voltage between the anode and the cathode OR the charged metal plates affects the path of an electron beam.
Inside of the tube contains A VACCUM.
When the heater current is increased, the number of electrons produced will INCREASE as well.
- Oscilloscopes are voltmetres that display how a voltage changes with time. They also show a real-time graph of how varibales (things that change) like temperature and pressure change over a period of time.
- They are used commonly to monitor the condition of patients on hospital (as you see in Grey's Anatomy).
- An electron gun in the oscilloscope fires electrons onto the screen to create an image.
- Cathode Ray Tubes (CTRs) are tubes with a vaccum containing one or more electron guns. Before flat screen TV's, CRTs were used in televisions and computer monitors as well.
- A voltage provides energy to the electrons flowing in an electric circuit.
- To calculate kinetic energy, KE, gained by one electron fired from an electron gun, you use the equation:
KE = Electronic charge x accelerating voltage or
KE= e * V (where e= 1.6x10^-19 Coulombs)
- Absolute Zero is the lowest possible temperature an object could be.
- Absolute Zero occurs at -273°C. Heat is generated via the movement of particles, and as they get slower, an object's temperature decreases. When the particles in an object come to a complete halt, they have no kinetic energy. The temperature -273°C is also called Zero Kelvin (or 0 K for short).
- To convert a temperature in degrees Celcius into Kelvin, you just add on 273. Simple, right?
- For example, 20°C = 293 K.
- If you double the kelvin temperature, the average kinetic energy of the particles in a gas also doubles. Kelvin and the average kinetic energy of the particles are directly proportional. If you had a graph of Kelvin vs average kinetic energy, you would see a straight line.
- If you were to measure temperatures below -200°C, you could not use a normal mercury thermometer. Instead, you would use a helium thermometer, as helium remains a gas down to -269°C.
- On Earth, the particles contunually collide against eachother and exert atmospheric pressure. The amount of pressure there is depends on how 'tightly packed' the particles are.
- In outer space, there is almost no pressure, while in the centre of a planet or star, there is a lot.
- The atmospheric pressure you normally experience is about 10N/cm² (or 100kN/m²)
- A way to increase pressure (the amount of collisions) is to increase the temperature. At a higher temperature, the molecules collide harder and more often. At higher temperatures there is a higher pressure.
- The equation for a gas in a sealed container is:
Pressure, P (Pa)
_____________ = constant
Gas Laws (1)
- The volume of air in a balloon depends on the number of particles it contains, the temperature, and the pressure in the atmosphere outside of the balloon. A weather balloon can be used to take measurements as it rises through the atmosphere.
- As it gains altitude, the pressure drops more than the temperature decreases and the balloon expands. At 35km, the balloon expands so much that it bursts, returning to Earth by parachute, with a record of the different weather conditions at different altitudes.
In a graph that shows volume (cm³) over pressure (kPa), we see that volume and pressure are inversely proportional.
Gas Laws (2)
- Volume is proportional to the kelvin temperature. If the kelvin temperature doubles the volume doubles, as long as the pressure does not change!
Gas Laws (3)
The points on this slide are really important, so revise this bit carefully!
The volume of gas in a sealed container is:
- Proportional to the Kelvin temperature (k). If T doubles, V doubles.
- Inversely proportional to the pressure (P). If P doubles, V halves
- From this, we can see that PV/T = constant
The gas equation to work out pressure changes is:
- P1 V1 P2 V2
----------- = ---------
- T1 T2
T = KELVIN! NOT C!!!
- An oscilliscope bends an electron beam using charged deflection plates, but in a television tube electromagnets deflect the electrons.The evacuated ray tube (evacuated means in a vaccum) of a colour television is a lot more complex than that of an oscilliscope.
- In an oscilli