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Some types of thermometer are filled with mercury, a liquid metal.

# Physics - The Kinetic Theory of Matter

This Physics quiz is called 'Physics - The Kinetic Theory of Matter' and it has been written by teachers to help you if you are studying the subject at senior high school. Playing educational quizzes is one of the most efficienct ways to learn if you are in the 11th or 12th grade - aged 16 to 18.

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The kinetic theory of matter is one of the models that scientists use to help them to make sense of the world around them. The word kinetic always suggests something is moving and this theory is about the movement of particles in solids, liquids and gasses. Particles transfer heat energy into kinetic energy. The kinetic theory can explain many properties of the three states of matter and is related to the amount of thermal energy distributed through the particles of an object. The particles in solids, liquids and gasses have different amounts of energy, are arranged differently and move differently too.

1.
What happens to the particles of water vapor as it changes from a gas into a liquid to form a film of water on the inside surface of a cold window?
When the particles of the water vapor hit the window, they stick to it
The particles lose energy to the cold surface, slow down and become closer together
The particles clump together because of the light coming through the window, forming water
The particles speed up, forming water droplets
When any gas is cooled its particles slow down and move closer together forming a liquid - they condense. Some gasses, like water vapor, condense easily but other gasses, like oxygen for example, need to be cooled well below 0oC before their particles slow down enough to become a liquid
2.
Some types of thermometer are filled with mercury, a liquid metal. Why do they work?
Mercury is a metal so it conducts heat into the thermometer
Mercury behaves in an unusual way
Particles of liquids expand when they are heated and contract when they are cooled so the mercury fills more or less of the thermometer depending on the temperature
The particles move faster or slower depending on the temperature so the mercury expands and contracts
Answer three may have been quite appealing to you but you should never talk about the particles expanding. They remain the same size, whether a substance is hot, cold or at room temperature; it is the speed at which they move and the space that they occupy that changes. Mercury is toxic and was replaced in later thermometers by a mixture of alcohol and water which works in the same way. Digital thermometers work in an entirely different way using a device called a thermocouple
3.
What will a substance do when it is heated?
It will expand
It will contract
It will burn
It will explode
Whilst some substances may well burn or explode, thankfully there aren't many of them!
4.
What happens to a gas in a sealed container when it is heated?
The gas explodes
The pressure of the gas increases
The gas implodes
The gas condenses
The pressure increases because the particles have more thermal energy so they hit the walls of the container with greater force
5.
Why are warm fluids less dense than their cold equivalent?
Some of the fluid escapes from the particles so they are lighter
Their particles are closer together
Hot particles lose their quarks and become lighter
Their particles are further apart
More thermal energy means that the particles of the fluid move faster and take up more space. This means that there are fewer particles in the same volume of warm areas of the fluid than in the cooler areas of the fluid, making it less dense
6.
Which states of matter contract when you cool them?
Only gasses
Only solids
Liquids and gasses
All of them
As the thermal energy is removed, the particles move less and can pack together more closely. Water is a bit odd - it contracts until you get to 4oC then it starts to expand. As it forms ice, it expands a lot, then, when you cool ice down, it contracts exactly as you would expect
7.
Why does hot air rise?
Heat naturally goes upwards
It is pushed there by the cold air
It is less dense than colder air
It doesn't, this is a myth
This causes a convection current as cold air moves in to take its place
8.
When a liquid is evaporating it cools down. Why?
The faster particles escape leaving the slower particles behind
There are fewer particles
Evaporation needs a breeze and breezes cool things down
It has a smaller volume than before
Slower moving particles have less thermal energy so the temperature of the liquid is lower. The cooling effect is more noticeable the faster that something evaporates
9.
According to the kinetic theory, what are the particles in a heated solid doing?
Vibrating more slowly than when the solid was cool
Vibrating more rapidly than when the solid was cool
Moving around more slowly than when the solid was cool
Moving around more rapidly than when the solid was cool
As any state of matter is heated, the movements of the particles increase
10.
Which of the following would increase the speed at which a liquid evaporates?
Covering the liquid with a beaker
Making sure that there were no drafts
Spreading it out over a larger area
All of the above
Answers one and two have exactly the opposite effect - they slow down the rate of evaporation. Not on the above list is temperature. Raising the ambient temperature (temperature of the surroundings) increases the rate of evaporation
Author:  Kev Woodward