P3

Kinetic theory says that gases consist of very small particles. Which they do – oxygen consists of oxygen molecules, neon consists of neon atoms. These particles are constantly moving in completely random directions. They constantly collide with each other and with the walls of their container. When they collide, they bounce off each other, or off the walls. The particles hardly take up any space. Most of the gas is empty space. If you increase the temperature of something, you give its more particles more energy as they move about more quickly or vibrate more. In the same way if you cool a substance down, you’re reducing the kinetic energy of the particles. The coldest that anything can get is –273 degrees Celsius which is absolute zero. At absolute zero, atoms have as little kinetic energy as it is possible to get. Absolute zero is the start of the Kelvin scale. A temperature change of one degree Celsius is also a change of 1 Kelvin. The scales are the same the only difference is where zero occurs. To convert Celsius to Kelvin add 273 and to convert Kelvin to Celsius minus 273. If you increase the temperature of a gas, you give its particles more energy. The temperature of a gas in Kelvin is proportional to the average kinetic energy of its particles.

As gas particles move about they bang into each other and whatever gets into their way. Gas particles are light, but they are not massless. When they collide with something they exert a force onto it. In a sealed container gas particles smash against the container walls creating an outward pressure. This pressure depends on how fast the particles are going and how often they hit the walls. If you heat a gas, the particles move faster and have more kinetic energy. This increase in kinetic energy means the particles hit the container walls harder and more often, creating more pressure.

If you add the same amount of gas in a bigger container, the pressure will decrease, cause there will be fewer collisions between the gas particles and the containers walls. When the volumes reduced the particles get more squashed up and so they hit the walls more often, hence the pressure increase. In a sealed container, constant is equal to pressure over temperature, Kelvin. If the volume is not constant then pressure one multiplied by Volume one over temperature one is equal to pressure two multiplied by volume two over temperature two.

Alpha is a helium nucleus, 4 2 He. It is slow, heavy and strongly ionising but can be stopped by paper and skin. Beta is an electron, 0 –1 e. It is light, fast, moderately ionising but can be stopped by thin metal. Gamma is electromagnetic radiation and has no mass. It is very fast and weakly ionising but can be stopped by thick lead or very thick concrete.

Positrons are just like electrons – they have exactly the same mass but they are…