Transfer of Thermal Energy (P2.3)

What is thermal conduction?

• The transfer of thermal energy through a substance

• The movement of particles in a gas

• The process of heating a fluid

• The emission of thermal radiation

Answer explanation

Thermal conduction is defined as the transfer of thermal energy through a substance, typically occurring in solids where heat moves from hotter to cooler areas. This distinguishes it from other processes like fluid heating or radiation.

Why does thermal conduction occur faster in metals than in non-metals?

• Metals have free electrons that speed up energy transfer

• Metals are denser than non-metals

• Metals have a higher specific heat capacity

• Metals are better insulators

Answer explanation

Thermal conduction occurs faster in metals because they have free electrons that facilitate rapid energy transfer, unlike non-metals, which lack these mobile charge carriers.

When does thermal conduction end?

• When the particles stop moving

• When the substance cools down

• When the substance is heated

• When thermal equilibrium is reached

Answer explanation

Thermal conduction ends when thermal equilibrium is reached, meaning there is no net heat transfer between substances. This occurs when their temperatures equalize, regardless of particle movement or heating/cooling.

What is thermal equilibrium?

• A state where temperature is constant

• A state of maximum energy transfer

• A state where all particles are at rest

• A state with no net energy transfer

Answer explanation

Thermal equilibrium is defined as a state with no net energy transfer between systems. This occurs when two systems reach the same temperature, resulting in no heat flow, making the correct choice 'A state with no net energy transfer'.

True or False: Thermal conduction does not happen in liquids or gases.

• Only in liquids

• Only in gases

• False

• True

Answer explanation

False is correct because thermal conduction occurs in all states of matter, including solids, liquids, and gases. In liquids and gases, conduction happens through molecular collisions and energy transfer.

What is a convection current?

• The transfer of heat through direct contact

• The vibration of particles in a solid

• The movement of fluid due to temperature differences

• The emission of thermal radiation

Answer explanation

A convection current is the movement of fluid caused by temperature differences, where warmer, less dense fluid rises and cooler, denser fluid sinks, creating a continuous circulation pattern.

What substance is used to demonstrate convection in water?

• Potassium permanganate

• Sodium chloride

• Sugar

• Vinegar

Answer explanation

Potassium permanganate is commonly used to visualize convection currents in water due to its distinct color. When added to water, it disperses as the water heats up, clearly demonstrating the movement of warmer water rising and cooler water sinking.

True or False: Heat is a substance that can rise.

• Only in solids

• True

• False

• Only in fluids

Answer explanation

Heat is not a substance; it is a form of energy. It cannot rise like a material object. Therefore, the statement is false.

What happens when a fluid is cooled?

• The particles move closer together and density increases

• The particles move further apart and density decreases

• The fluid expands and rises

• The fluid becomes a solid

Answer explanation

When a fluid is cooled, its particles lose energy and move closer together, resulting in an increase in density. This is why the correct answer is that the particles move closer together and density increases.

True or False: All objects emit thermal radiation.

• Only solid objects

• Only hot objects

• False

• True

Answer explanation

True. All objects, regardless of their state (solid, liquid, or gas) and temperature, emit thermal radiation. This emission occurs due to the motion of particles within the object.