Grades 11 and 12 | Physics | Senior High School | Physics

Physics: Senior High School: 11th and 12th Grade Quiz - Physics - The Kinetic Theory of Matter (Questions)

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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.

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The kinetic theory explains why substances freeze and melt, why they boil and condense, and why evaporation causes cooling. It helps to explain why heat can be conducted by solids, how convection occurs in fluids and much more... including why solids cannot be compressed but gasses can. In solids the particles are close together and fixed in place. Their only movement is to vibrate. Because of this, solids have definite shapes which they will keep - unless they are broken or cut. It is very difficult to push the particles in solids any closer together and so they can't be compressed.

In liquids the particles are only a little further apart than in solids, so liquids can't be compressed either. The main difference is that the particles in a liquid are free to move past each other, which is why liquids flow and take up the shape of the container in which they are placed. This movement was something that was first noted in 1827 by botanist Robert Brown. Brown observed that pollen grains floating on water moved around in random directions. It then took about 75 years until Albert Einstein came up with an explanation - water molecules were colliding with and pushing the pollen grains around.

Finally, in gasses the particles are far apart and moving extremely rapidly in random directions. Because the particles are so widely spaced, gasses are easily compressed.

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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

What will a substance do when it is heated?

[ ]	It will expand
[ ]	It will contract
[ ]	It will burn
[ ]	It will explode

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

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

Which states of matter contract when you cool them?

[ ]	Only gasses
[ ]	Only solids
[ ]	Liquids and gasses
[ ]	All of them

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 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

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

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

10.

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

Physics: Senior High School: 11th and 12th Grade Quiz - Physics - The Kinetic Theory of Matter (Answers)

According to the kinetic theory, what are the particles in a heated solid doing?

[ ]	Vibrating more slowly than when the solid was cool
[x]	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

What will a substance do when it is heated?

[x]	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!

Why does hot air rise?

[ ]	Heat naturally goes upwards
[ ]	It is pushed there by the cold air
[x]	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

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
[x]	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

Which states of matter contract when you cool them?

[ ]	Only gasses
[ ]	Only solids
[ ]	Liquids and gasses
[x]	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 4^oC 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

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
[x]	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 0^oC before their particles slow down enough to become a liquid

When a liquid is evaporating it cools down. Why?

[x]	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

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
[x]	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

What happens to a gas in a sealed container when it is heated?

[ ]	The gas explodes
[x]	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

10.

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
[x]	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