THERMAL ENERGY

WEEK TWO LESSON NOTE ON BASIC SCIENCE FOR J S S 2

THERMAL ENERGY

SPECIFIC OBJECTIVES: At the end of this lesson, students should be able to;

1. Define thermal energy.
2. Explain the concept of heat flow.
3. List and describe three methods of heat transfer.
4. State real life applications of heat conduction.

Meaning: Thermal energy is the energy that is transferred from one place to another due to differences in temperatures. It is the energy present in hot objects. It is also called the energy of hotness. Heat energy flows from a hot region (hot object) to a cold region/object. The primary source of energy is the sun. We make use of energy from the sun in forms of heat and light energies. Heat energy is measured using a calorimeter.

Heat flow: This is the movement of heat energy from a region of higher temperature to a region of lower temperature. When two objects/bodies are in contact, heat flows from a hotter body to a cooler body.

Methods of Heat Transfer

Heat energy can be transmitted in three major ways;

1. Conduction
2. Convection
3. Radiation

1. Conduction: This is the process by which heat energy is transferred from a region of higher temperature to a region of lower temperature along a solid material. Particles of solids are closely packed together and are constantly vibrating. When one end of a rod (solid) is heated, the particles at that end gain heat energy and begin to vibrate. The heat energy is transferred to the particle next to it. This process continues until the heat energy reaches the other end of the rod.

Objects that allow heat to flow or pass easily through them are called conductors while those that do not allow heat to flow through them are called insulators or bad conductors. Objects that do not allow easy flow of heat through them are called semi-conductors. Conductors are mostly metals such as copper, silver, nails, etc.  Conduction is the major method of heat transfer in solids.

2. Convection:  This is the process by which heat energy is transferred from one part of a liquid/fluid to another by the movement of the molecules of the liquid. Molecules of the liquid (e.g water) that is being heated acquire heat energy and rise up while the molecules of cool water above sink down to replace the molecules of hot water at the bottom. In this way, heat is transferred to the cold molecules. This circulation of liquid molecules creates convection current within the liquid. Convection occurs in fluids (liquids and gases).
3. Radiation: This is the process by which heat energy is transferred from one place to another without the aid of a material medium. It involves the transfer of heat energy from place to place through the empty space in the form of waves. Medium does not play an active part in radiation. Heat from the sun reaches the earth by radiation.

Applications of Heat Conduction

Some real life applications of heat conduction include;

• Heat from electric or charcoal iron is conducted to the shirt/cloth which makes it easy to iron out all the unsightly wrinkles.
• When a cube of ice is placed on the palm, heat is conducted from the palm to the ice and it melts.
• When we walk outside on bare feet on a hot day, heat from the asphalt is conducted to the feet and they become hot.
• A cold stainless plate becomes hot after some minutes when food is placed on it due to the conduction of heat from the cooked food to the plate.
• When we pick a coin, it feels cold but after few minutes, the heat from the palm is conducted to the metal coin.

EVALUATION: Students should answer the following questions;

1. What is thermal energy?
2. Briefly explain the concept of heat flow.
3. Discuss any two methods of heat transfer.
4. State three applications of heat conduction
5. Give two examples each of conductors and insulators.

ASSIGNMENT

1. Tabulate three differences between heat and temperature
2. State two effects of heat energy on matters.
3. List any three sources of heat energy.
4. Calculate the kinetic energy of a man of mass, 50kg moving with an average speed of 15m/s.
5. State the law of conservation of energy.