Energy and heat

1. How is temperature measured?
2. What is absolute zero?
3. What is energy?
4. How is energy conserved?
5. Where does our energy come from?

Electricity

1. What is a volt?
2. What is a semiconductor?
3. How do electric currents flow?
4. Complex electrical circuits can be printed on to a tiny silicon chip. True/false?
5. What is resistance?

[ Answers]

Energy and heat

1. Temperature is usually measured with a thermometer. Some thermometers have a metal strip that bends according to how hot it is, but most contain mercury in a tube. You may have had a thermometer placed under your tongue or armpit to check how high your body temperature is whenever you are feeling feverish. The thermometers used to measure air temperatures are much bigger and different to the ones used by doctors. However, like in all thermometers, the mercury level in the tube expands and the level rises to indicate the temperature.

2. Absolute zero is the coldest possible temperature; the temperature at which atoms stops moving altogether. This happens at -273.15 degrees Celsius or 0 on the Kelvin scale.

3. Energy takes many forms; there is heat energy which boils water, chemical energy which fuel vehicles and electrical energy which drives machines and keeps lights glowing.

Almost every form of energy can be converted into other forms. Energy is essentially the capacity for making something happen - or ‘doing work’ as scientists say.

4. As energy cannot be created or destroyed even when it’s converted into another, from one form to another, it is always conserved; there is always the same amount of energy as there was before, no matter what process it has been through.

5. Nearly all of our energy comes ultimately from the Sun. Some are obtained directly via solar power cells, while others indirectly via fossil fuels such as coal and oil. Coal and oil get their energy from fozzilised plants and other organism of which they are made.

Plants get their energy directly from the sun, by a process called photosynthesis.

Electricity

1. Electrical current flows as long as there is a difference in charge between two points in the circuit. This difference is called a potential and is measured in terms of volts. The bigger the difference, the bigger the voltage.

2. Materials such as silicon or germanium, which are partly resistant to electric current and partly conducting, are known as semi-conductors. They can be set up so that the conductivity is switched on or off, creating a tiny electrical switch. They are used to make diodes, transistors and chips, and so, are essential to electronics.

3. The charge in an electric current is electrons that have broken free from their atoms. None of them moves very far, but the current is passed on as they bang into each other, like rows of marbles.

4. True.

5. Not all substance, conduct electric current well. A substance’s ability to block the flow of electric current is what is known as resistance.