SUBJECT : BASIC SCIENCE AND TECHNOLOGY
CLASS : JSS2
TERM : SECOND TERM
WEEK : WEEK 4
PREVIOUS KNOWLEDGE :
Energy transfer when work is done.
BEHAVIOURAL OBJECTIVES : At the end of the lesson , pupils should be able to
- define thermal energy
- explain heat flow
- explain conduction
Topic: Thermal Energy
Energy transfer is the process of transmitting or transferring energy from one place to another. The word thermal means heat. Thermal energy is the transfer of heat from one place to another.
Energy transfer means that energy moves from one place to another (without changing form). The process of heat flow from the sun to us is referred to as radiation. The process of heat flow from the soup to the spoon discussed is referred to as conduction. There is the third process of heat flow known as convection. Therefore, heat flow means that heat energy is transferred from a hotter part of an object to the cooler part of the object. Heat is a form of energy that flows from a hot area to a cold one. When you are in the hot sun, you feel hot. The heat travels from the sun through the atmosphere to your skin. When you put a kettle of cold water on fire, the water gets hot. The heats flows or travels from the fire through the kettle into the water.
Transfer of Heat Energy
The three processes of heat transfer are conduction, convection and radiation.
When particles in a matter (or substance preferably a metallic substance) are heated, the particles vibrate, hitting the successive ones (which are not in contact with the source of heat). This raises their temperature until all the particles in the metallic substances are heated up. In this way, heat is being conducted along the metallic substance and this process is called conduction.
Usually, heat flows from a hot to a cold body. You know that heat is a form of energy and a hot body has energy stored up (in form of potential energy) in it. In order to convert this potential energy into kinetic energy, heat then passes to another particle which has lower energy. Therefore, a hot body must lose heat energy to a cooler one.
There are good conductors and bad conductors of heat.
Good conductors of heat are substance s, which conduct heat readily; all metals are good conductors of heat.
Bad conductors are substances that do not conduct heat readily. Liquids and gases are bad conductors of heat. Water is an example of a bad conductor of heat. But mercury is a metallic liquid, hence it conduct heat readily.
Heat transfer in convection is peculiar with liquids. The heat flows from the bottom of a liquid container to the top by the actual movement of the liquid molecules. This transfer of heat by the movement of liquid molecules is known as convection
Radiation is a method of heat transfer that does not require material medium for transmission. Heat energy is transmitted by means of waves. Heat energy from the sun reaches us by radiation. Heat can travel in invisible waves from hot places to cooler places. Heat travelling this way does not need any medium (solids, liquids or gases) to travel through. Heat can travel through a vacuum. A vacuum is a space in which there is nothing at all, not even air. There is a vacuum in space between the earth and the sun. The heat from the su travels through this vacuum to the earth and through the earth to other obects.
Summary of the Three Types of Heat Transfer
Diagram of the Three Types of Radiation
- Define Radiation?
- The three processes of heat transfer are___
- What is energy transfer?