Learning objectives
- Differentiate heat from temperature.
- Describe conduction, convection and radiation.
- Identify conductors and insulators.
- Explain common heating and cooling examples.
Heat is energy transfer
Heat is energy transferred because of a temperature difference. Temperature measures how hot or cold a body is. Heat naturally flows from a region of higher temperature to a region of lower temperature until thermal balance is reached.
A thermometer measures temperature. Laboratory thermometers and clinical thermometers are designed for different ranges and uses.
Three methods of heat transfer
Conduction mainly occurs in solids when faster-moving particles transfer energy to neighbouring particles. Metals conduct heat well because energy moves through them easily.
Convection occurs in liquids and gases. Warmer, less dense fluid rises while cooler, denser fluid sinks, forming convection currents. Radiation transfers energy by electromagnetic waves and does not require a material medium.
Conductors and insulators
Cooking utensils often use metal for the body because it conducts heat, but handles are made from wood or heat-resistant plastic because these materials are poor conductors.
Woollen clothes reduce heat loss by trapping air. Air is a poor conductor, so the trapped layer slows energy transfer from the body.
Practice questions with explanations
Try each question before opening the answer. The explanation shows the reasoning, not only the final response.
Q1. What is the difference between heat and temperature?
Answer: Heat is energy transfer; temperature measures hotness or coldness.
Explanation: The two are related but are not the same physical quantity.
Q2. In which direction does heat flow naturally?
Answer: From higher temperature to lower temperature.
Explanation: Transfer continues until temperatures become equal.
Q3. Which mode of heat transfer is strongest in solids?
Answer: Conduction.
Explanation: Particles pass energy to neighbouring particles without bulk movement of the solid.
Q4. Why is copper used in cookware?
Answer: Copper is a good conductor of heat.
Explanation: It transfers heat quickly and spreads it across the utensil.
Q5. Why are saucepan handles often plastic?
Answer: Plastic is a poor conductor.
Explanation: It reduces heat transfer to the hand.
Q6. What causes convection currents?
Answer: Differences in temperature and density within a fluid.
Explanation: Warm fluid rises and cool fluid sinks.
Q7. How does heat from the Sun reach Earth?
Answer: By radiation.
Explanation: Radiation can travel through the vacuum of space.
Q8. Why do dark surfaces become hotter in sunlight?
Answer: They absorb more radiation.
Explanation: Dark, dull surfaces are generally better absorbers than light, shiny surfaces.
Q9. Why do woollen clothes keep us warm?
Answer: They trap insulating air.
Explanation: The trapped air slows heat loss from the body.
Q10. What happens when a hot object touches a cold object?
Answer: Heat transfers to the colder object.
Explanation: The temperature difference drives the transfer.