UNIT 7. ENERGY (NATURAL SCIENCE)

UNIT 7. ENERGY

FORMS OF ENERGY

LIGHT

Light is a form of energy  and can be produced by natural sources (the sun, for example) or artificial sources (like a candle).

·         Reflection and mirrors

When light hits an object, it reflects . If the surface is smooth, all the rays reflect in the same direction but if the surface is rough, the rays reflect in different directions. Mirrors reflect the rays of light and form an image of the object that is in front of it.

·         Refraction and lenses

Refraction occurs when light changes direction because it passes from one substance to another with a different density. The substance is called medium.

Lenses are pieces of curved glass or plastic that make bigger or smaller objects, depending on the shape of the lens.

·         Electricity from light

Solar panels produce electricity using the energy of the sun.

·         How do we see colours?

Sunlight is an example of White light, that is made up of seven colours that we see when light passes through a prism. We don´t have to mix the seven colours to produce White light, with the primary colours is enough: red, blue and green.

When light hits an opaque object, some colours are absorbed and others are reflected.  The color we see is the color that the object reflects, the rest are absorbed.

HEAT

All matter has thermal energy.

·         Three ways of transferring  heat

Particles in matter are always moving and with more movement, they produce more heat.  When two particles collide heat is transmitted from the fastest and hottest particles to the the slowest and coolest one.  When the temperature is the same in all the material it is called termal equilibrium.

A.      Radiation: heat waves radiate from a hot object or a source of heat.

B.      Convection: it is the transfer of heat. When the particles heat up, they rise up and cooler particles go down, producing a circular movement.

C.      Conduction: direct contact between materials let the pass of heat. For example, metals are very good termal conductors.

·         Thermal conductors and insulators

Thermal energy goes from a warm substance to a cooler one.  This flow of termal energy is heat.

Some materials transfer heat, but others don´t.

-          Thermal insulators: do not transfer heat. For example, Wood, wool, plastic.

-          Thermal conductors: transfer heat. Metals like iron or copper are very good conductors.

·         Effects of termal energy

-          Melting: the termal energy in a solid increases and it becomes a liquid.

-          Evaporation: the termal energy in a liquid increases and it becomes a gas.

-          Expansion: the termal energy of a substance increases and the volucme increases too.