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Photon Learning

About the Blog

This blog is designed as a library of 'thoughts' and concepts for the students of Excel@Learning. It tries to speed up and simplify learning about core subjects including English, Maths and Sciences (Natural, Applied and Islamic) by breaking up topics into independent 'thoughts' or 'photons' of learning. You can contact us at . You can click to return to the Main Web Site.

Changes of State

Physics Posted on Tue, April 02, 2013 21:26:39

If you tried to stir hot cooking oil with a plastic spoon, the plastic would melt. Plastic is solid. This means that it will remain solid at temperatures and pressures normally found on Earth. But change the circumstances, and you can change the normal state of a substance. In the same way, if you put orange juice, normally a liquid, into a freezer, it will go solid. And if you breathe onto a cold windowpane, the water vapour in your breath (normally a gas) will condense into drops of liquid. If the sun shines on them, the heat turns them back into a gas and they evaporate into the air again. Even the hardest rocks melt at the very high temperatures and pressures found underneath the Earth’s crust. Most substances that we know will change state when the temperature or pressure changes enough.

From Solid to Gas
If you heat a solid to a special temperature called the melting point, it will melt into a liquid. If you heat it even more, it gets to a point when the liquid changes into a gas. This is the boiling point. At the boiling pint, all particles in a liquid get enough energy from the heat to break free from each other. Then bubbles of gas form in the liquid. Liquids are always slowly changing to gas, even below boiling point. This is called evaporation.

Cold glasses get little droplets of water on them because water vapour from the air turns back into water on the cold glass. Cold glass removes the energy from the particles and so turns them into liquid.

Why does wet ink dry? Because the water in it turns into water vapour and evaporates into the air. Some of the water particles get enough energy to escape and form the gas.


Sometimes a solid turns straight into a gas. This is called sublimination. It is what happens with dry ice, used to make dramatic looking clouds on stage in a theatre. Dry ice is really frozen carbon dioxide. It is called dry because it does not become liquid before turning into a gas.

Particles in a solid are packed tightly together. But when heated, they vibrate more and more until they can break free of fixed positions, and move freely over each other. The solid turns into a liquid.

A dripping candle will soon freeze into a solid if you blow it out. This is because the particles which are sped up by the heat of the flame, slow down again and move closer together when the heat is removed. When they slow down enough, they get locked into position again, forming a solid.

Pressure Cooking
The temperature at which liquid boils (boiling point) depends on the pressure around it. When the pressure goes down, the boiling point goes down because the molecules can escape as a gas more easily. When the pressure goes up, the boiling point goes up because it is more difficult for the molecules to escape. In pressure cookers, the increased pressure raises the water’s boiling point. At the higher temperature, the food cooks more quickly.

States of Water
Water is unusual because it can be found in all three states of matter in everyday life. In solid form it is ice, in liquid form, water, and in gaseous form, water vapour. The properties of water in these three states are important to everything on Earth. For example, plants and animals need water regularly to survive.

Water Cycle
The never ending cycle between the different states of water is essential to everything on earth. Liquid water evaporates and solid snow sublimes into the air. Water vapour condenses into droplets to form clouds. Water droplets fall back to earth as rain or snow.
The never ending water

Water Vapour
When the temperature is high, water evaporates quickly. In the warm, tropical forests of South America, there is plenty of rain and because the temperature is high, water evaporates all the time. The water vapour in the air makes it very humid, and means that special types of plants, such as certain orchids, can thrive. They take all the moisture they need straight from the air, not the ground.

Steam Power
When water boils, it turns into steam. Steam is water vapour that is hot. Being a gas, it takes up much more space than the liquid it came from. It is full of energy and can be used to drive heat engines such as the steam turbine. It enters the turbine at high temperature and pressure, and drives the turbine wheels around.

Changes with Pressure
Pressure can bring about a change of state. It is possible to ice skate because the skates move over a thin layer of water. The weight of the skater is concentrated into the blade which makes the ice melt as the skate moves over it.

Expanding Ice
Have you noticed how pipes often burst in freezing weather? This is because the water inside them expands as it freezes into a solid.

From the Dorling Kindersley Science Encyclopaedia.

Sates of Matter

Physics Posted on Sat, March 16, 2013 15:57:25

Imagine a mountain, a river, and the air around them. These three things represent the three states of matter. The mountain is made of rock which is solid. The river is made of water, which is liquid and the air around them is made of gas. Most solids are hard and have a definite shape and volume but some, for example rubber, have a shape that can be changed. Liquids don’t have a definite shape but they have a fixed volume and can flow. Gases can also flow and have no definite shape or volume. You can’t see most gases. Because both liquids and gases can flow they are called fluids. The three states of matter behave the way they do because the particles they are made of can move in different ways.

Gases can quickly fill any space they are put in because their particles move very fast. This means that they do not have a volume or shape of their own but take the shape of their containers. Things can pass through a gas very easily because the particles are far apart. That’s why we can walk through air and not feel a thing.

Liquids take the shape of their container. The particles in a liquid attract each other and stick together in bundels which slide past each other and move around.

A solid, such as a book, has a definite volume and a fixed shape that is not easy to change because the particles in a solid are linked together with strong bonds. The particles are packed so close that they cannot move; they only vibrate.

There is a fourth state of matter, called Plasma. It is not often seen because it only exists inside the Sun and other stars at very high temperatures, or on earth at low pressures. It is made up of atoms split up by electricity or great heat.

By Saima Rahman


Physics Posted on Mon, March 11, 2013 22:04:58


Everything you can think of, from the book you are holding, to the chair that you are sitting on, to the water that you drink, is made up of matter. But matter is not just things that you can touch. It includes the air that you breathe. The planets in the Universe, living things such as insects, and non-living things such as rocks are also made of matter. All matter is made up tiny particles called atoms, which are themselves made up of even smaller particles, called subatomic particles. Chemistry involves studying what matter is made of, and how atoms join together to make different things.

Creation of Matter

Most scientists believe that all the matter in the Universe was created in an explosion called the Big Bang. Great heat and energy followed the explosion. Then, after just a few seconds, some bundles of the energy turned into tiny particles. The particles turned into the atoms that make up the Universe that we live in today.

Non-Living Matter

Most matter in the Universe is non-living. This means that it does not grow, reproduce, or move itself about. A good example of non-living matter is the rock that makes up the Earth that we live on.

Living Matter

The Earth is home to many living things, including plants and animals of all kinds. Although a butterfly seems very different from a rock, they are both made of atoms. The atoms just join up in a different way to create something else.

Particles of Matter

Scientists use a bubble chamber to identify subatomic particles. The bubble chamber contains liquid hydrogen near its boiling point. Subatomic particles travelling through the liquid cause it to boil, leaving trails of bubbles. Although the particles are invisible, the trails that they leave can be seen and are different for each type of particle.

Founders of Chemistry

The French chemist Antoine Lavoisier (1743-94) is thought of as the founder of chemistry. Antoine showed that burned substances are heavier than unburned substances. He concluded that this was because the burned substances gained a gas, oxygen. Marie Lavoisier (1758-1856) worked with her husband by translating scientific works and campaigning for acceptance for their ideas.

Origins of Chemistry

Hundreds of years ago, before anyone knew about atoms, people called alchemists tried to find out what things were made of. They tried to turn metals such as lead into gold. They also searched for a medicine that would give eternal life. They tried without success. Many alchemists were women. One name for alchemy, opus mulierum, is Latin for women’s work.

From the Dorling Kindersley Science Encyclopaedia


Physics Posted on Fri, February 10, 2012 20:28:03

Stars are large balls of gas in space. Our ‘Sun’ is a star too. Watch the following video about stars to get an idea about different stars and how large they can be:

Space (Astronomy)

Physics Posted on Mon, January 16, 2012 23:32:35

In Key Stage 3, the following topics are taught under the heading:


1. The Universe/ Multiverse.
2. Origins of the Universe.
3. Galaxies.
4. Stars.
5. The Life cycle of stars.
6. Constellations.
7. The Solar System.
8. The Sun.
9. Mercury
10. Venus
11. The Earth.
12. The Moon
13. Mars.
14. Asteroids
15. Jupiter
16. Saturn.
17. Uranus.
18. Neptune.
19. Pluto.
20. New Planets.
21. Natural Satellites.
22. Comets.
23. Meteors.
24. Studying Astronomy.
25. Telescopes.
26. Rockets.
27. Satellites.
28. Space probes.
29. Space travel.
30. Space stations.

Weather (Meteorology)

Physics Posted on Mon, January 16, 2012 23:23:17

In Key Stage 3, the following topics are taught under the heading:


1. Sunshine.
2. Seasons.
3. Climates.
4. Climate change.
5. Sky (Atmosphere).
6. Air pressure.
7. Temperature (hotness).
8. Humidity (how wet the air is).
9. Weather Fronts.
10. Winds (moving air).
11. Wind strength (speed).
12. Thunder and Lightning.
13. Hurricanes.
14. Tornadoes.
15. Clouds.
16. Cloud formation.
17. Low clouds (fog, mist and smog).
18. Rain.
19. Snow.
20. Hail.
21. Frost, dew and ice.
22. Special effects.
23. Weather forecasting.
24. Weather watching.

Earth (Geology)

Physics Posted on Mon, January 16, 2012 22:47:45

In Key Stage 3, the following topics are taught under the heading:


1. Formation of the Earth.
2. Structure of the Earth.
3. Moving continents.
4. Volcanoes.
5. Mountain building.
6. Earthquakes.
7. Rocks and minerals.
8. Igneous rocks.
9. Sedimentary rocks.
10. Metamorphic rocks.
11. Fossils.
12. Record in the rocks.
13. Ice and glaciers.
14. Weathering and erosion.
15. Soils.
16. Rivers.
17. Seas and Oceaons.
18. Waves, Tides and Currents.
19. Shoreline.
20. Coal.
21. Oil and gas.
22. Mapping the Earth.

Sound and Light (Waves)

Physics Posted on Mon, January 16, 2012 22:43:48

In Key Stage 3, the following topics are taught under the heading:

Sound and Light.

1. Sound.
2. Measuiring sound.
3. Loudness.
4. Making and hearing sound.
5. Reflection and absorption.
6. Musical sounds.
7. Sound recording.
8. Electronic sounds.
9. Light.
10. Electromagnetic spectrum.
11. Sources of light.
12. Reflection.
13. Refraction.
14. Lenses.
15. Optical instruments.
16. Lasers.
17. Light and Matter.
18. Shadows.
19. Colour.
20. Colour subtraction.
21. Vision.
22. Photography.
23. Cinema.

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