A metal rod is heated at one end. The other end slowly becomes hot too, even though it was not directly heated. Which mechanism of heat transfer is responsible?

Convection — warm air carries heat along the surface of the rod Radiation — the hot end emits infrared waves that warm the other end Conduction — thermal energy is passed from particle to particle along the rod Evaporation — heat escapes as water vapour from the hot end

Metals are far better conductors of heat than wood or plastic. Why?

Metal atoms are heavier, so they vibrate more powerfully Metals have free electrons that move through the material and carry thermal energy rapidly from hot regions to cool ones Metal atoms are packed closer together, so heat has less distance to travel Metals reflect heat inward rather than letting it escape

In which states of matter can convection occur?

Solids only — particles are close enough to push each other Liquids only — gases are too spread out Liquids and gases — convection requires matter that can flow All states of matter, including solids

What drives convection currents in a liquid or gas?

Heat rises on its own because it is lighter than cold Warmer fluid expands, becomes less dense, and rises; cooler denser fluid sinks to replace it, creating a circulation loop Cold particles sink because they weigh more individually Gravity pulls heat downward while buoyancy pushes cold upward

The Earth is about 150 million kilometres from the Sun, with a vacuum between them. Heat from the Sun still reaches Earth. Which mechanism makes this possible?

Conduction — heat travels through the thin gas between Earth and the Sun Convection — solar wind currents carry hot gas from Sun to Earth Radiation — the Sun emits electromagnetic waves (including infrared) that can travel through empty space Gravity — gravitational waves carry thermal energy across space

Why can radiation transfer heat through a vacuum, while conduction and convection cannot?

Radiation moves faster than conduction or convection, so it escapes the vacuum before being absorbed Radiation travels as electromagnetic waves, which do not need particles to propagate — conduction and convection both require physical matter to be present Conduction and convection only work downward; radiation works in all directions including upward into space Radiation is a property of metals only — non-metals cannot emit it

You are cooking pasta and the metal pot handle becomes too hot to touch, even though it is not over the flame. Which heat transfer mechanism is responsible?

Convection — warm air from the flame circulates up to the handle Radiation — infrared from the flame reaches the handle directly Conduction — heat travels through the solid metal from the hot base to the handle Evaporation — steam from the water heats the handle

You turn on a central heating radiator. Soon, warm air collects near the ceiling and cooler air stays near the floor. Which mechanism is responsible?

Conduction — heat travels through the air molecules touching the radiator Radiation — the radiator emits infrared that heats only the ceiling Convection — air heated by the radiator expands, rises, and is replaced by cooler air flowing in at the bottom Condensation — warm water vapour from the radiator rises to the ceiling

A vacuum flask (Thermos) keeps hot drinks hot for hours. It has two glass walls with a vacuum between them, and the glass surfaces are silvered. How does each feature reduce heat loss?

The vacuum stores cold air that cancels out heat; the silver attracts heat inward The glass walls conduct heat very slowly; the silver makes the flask look shiny The vacuum eliminates conduction and convection (no matter to carry heat); the silvered surfaces reflect infrared radiation back inward, reducing radiative heat loss The vacuum prevents evaporation; the silver traps convection currents inside the flask

Double-glazed windows have two panes of glass with a gap of still air (or argon gas) between them. Compared with single-pane glass, which mechanism of heat loss do they mainly reduce?

Radiation — the second pane of glass blocks all infrared waves from passing through Convection — the gap contains a special gas that absorbs convection currents Conduction — the air or argon gap is a poor conductor, and because it is trapped it cannot form convection currents, so very little heat crosses the gap Evaporation — moisture trapped between the panes absorbs heat as it evaporates