Transfer of Heat
📚 Topic Overview: Transfer of Heat
Transfer of heat occurs in three main ways: conduction, convection, and radiation.
These ideas are used in cooking, building design, weather, industry, and daily life.
Understanding the differences between them helps to answer concept-based,
application-based, and reasoning questions in science-based competitive exams.
1. Conduction
Concept / Theory
Conduction is the transfer of heat through a solid without the movement of the material
as a whole. Heat travels from the hotter part to the colder part by the vibration and
collision of particles. Metals are good conductors of heat, while wood, plastic, and
rubber are poor conductors (insulators).
Analogy / Examples
- A steel spoon placed in hot tea becomes hot from the dipped end to the handle.
- A metal rod heated at one end gradually becomes hot along its length.
Key Comparison (Good vs Poor Conductors)
| Good Conductors | Poor Conductors (Insulators) |
|---|---|
| Metals like copper, aluminium, iron | Wood, plastic, rubber, air |
| Used for cooking utensils, electric irons | Used for handles, coverings, protection |
| English | Telugu |
|---|---|
| Conduction | ఉష్ణ వాహకత్వం |
| Conductor | వాహక పదార్థం |
| Insulator | నిర్వాహక పదార్థం |
In household gas stoves, the vessel is usually made of a metal like aluminium or
stainless steel. Heat from the flame reaches the food quickly by conduction through
the metal base.
If heat transfer happens mainly in solids without
bulk movement of the material, the correct process is usually conduction.
2. Convection
Concept / Theory
Convection is the transfer of heat in liquids and gases by the actual movement of
warmer and cooler particles. Warmer, lighter (less dense) portions move up, and
cooler, heavier portions move down, creating convection currents.
Analogy / Examples
- When water is heated in a vessel, hot water rises and cold water sinks.
- Sea breeze and land breeze along coastal areas are due to convection of air.
Convection in Daily Life
| Situation | Convection Role |
|---|---|
| Water boiling in a pot | Hot water rises, cold water sinks; heat spreads evenly |
| Chimneys in kitchens | Hot air and smoke rise up and escape |
| Sea and land breeze | Air above land and sea heats differently, causing winds |
| English | Telugu |
|---|---|
| Convection | ఉష్ణ ప్రవాహం |
| Convection current | ప్రవాహ ధార |
| Sea breeze | సముద్ర గాలి |
In coastal villages, people experience cool air from the sea during the day
(sea breeze) and from the land at night (land breeze). This is due to convection
of air caused by unequal heating of land and water.
Whenever the question involves liquids or gases moving
up and down due to heating, think of convection.
3. Radiation
Concept / Theory
Radiation is the transfer of heat in the form of waves from a hot body to its
surroundings without the need for any medium. Heat from the Sun reaches Earth
through radiation, as space has almost no matter to conduct or convect heat.
Analogy / Examples
- Feeling warmth on your face when you stand in sunlight.
- Feeling heat when you stand near a burning fire, even without touching it.
Comparison Table: Conduction, Convection, Radiation
| Mode | Medium | Key Feature | Main Example |
|---|---|---|---|
| Conduction | Best in solids | No bulk movement of matter | Metal spoon in hot tea |
| Convection | Liquids and gases | Movement of warmer and cooler parts | Boiling water, breeze |
| Radiation | No medium needed | Heat travels as waves | Heat from the Sun |
| English | Telugu |
|---|---|
| Radiation | ఉష్ణ వికిరణం |
| Heat waves | ఉష్ణ తరంగాలు |
| Medium | మాధ్యమం |
Solar cookers use reflecting mirrors to focus sunlight onto a cooking pot. Heat
reaches the pot by radiation, allowing food to cook without conventional fuel.
If heat is received from a source without contact
and without air movement being the main reason, the process is most likely radiation.
4. Exam Tips & Tricks, Memory Sheet & Sample Questions
Short Memory / Formula Sheet
- Conduction → solids, no bulk movement, particle-to-particle transfer.
- Convection → liquids and gases, bulk movement, convection currents.
- Radiation → no medium needed, travels as waves, Sun to Earth.
- Good conductors: metals (copper, aluminium, iron).
- Poor conductors/insulators: wood, plastic, rubber, air.
- Dull, dark surfaces absorb more heat; shiny surfaces reflect more heat.
Quick Comparison Table (One-Glance Revision)
| Mode | Best Medium | Movement of Matter | Typical Example |
|---|---|---|---|
| Conduction | Solids | No bulk movement | Iron rod heated at one end |
| Convection | Liquids, gases | Bulk movement (up & down) | Boiling water, wind |
| Radiation | Vacuum or any medium | No matter needed | Sunlight warming skin |
Typical Sample Question Ideas (for Practice)
- Why are cooking utensils made of metal but their handles made of wood or plastic?
- Explain how sea breeze is formed using the idea of convection.
- Why do people in hot regions prefer light-coloured clothes?
- Which mode of heat transfer is mainly responsible when you feel warmth from a campfire at a distance?
- Match the following: (Conduction, Convection, Radiation) with suitable examples.
When solving questions, first identify the state of matter
solid / liquid / gas and check whether there is movement of
matter or not. This simple filter helps quickly decide between conduction,
convection, and radiation.