Thermal Energy – Practice Questions

What is a scientific model?

A representation used to explain and predict scientific phenomena

Why are scientific models useful?

They simplify complex systems and help predict outcomes

Types of scientific models

Physical, conceptual, mathematical, computational

What is a conceptual model?

An idea or diagram used to explain how something works

Advantage of conceptual models

Simple and easy to understand

Limitation of conceptual models

May oversimplify reality

How did the atomic model change (1800–1930)?

Solid sphere → plum pudding → nuclear model → Bohr model

What did Rutherford discover?

A small, dense, positively charged nucleus

How did technology help Rutherford?

Gold foil experiment using radiation detection

Why is Bohr’s model taught?

Simpler and explains energy levels clearly

Particle theory of matter

All matter is made of particles, particles move, have spaces, and attract each other

Particles in a solid

Closely packed, vibrate in place

Particles in a liquid

Close together, move past each other

Particles in a gas

Far apart, move freely and quickly

Distance between particles

Smallest in solids, larger in liquids, largest in gases

Temperature

Average kinetic energy of particles

Thermal energy

Total energy of all particles

Heat

Energy transferred due to temperature difference

Difference between heat and temperature

Heat is energy transfer, temperature is particle motion

Effect of increasing temperature

Particles move faster

Three types of heat transfer

Conduction, convection, radiation

Conduction

Heat transfer through direct contact

Convection

Heat transfer by movement of fluids

Radiation

Heat transfer by electromagnetic waves

Conduction in solids

Particles vibrate and transfer energy to neighbors

Why metals are good conductors

Free electrons carry energy quickly

Convection in fluids

Warm fluid rises, cool fluid sinks

Why warm fluid rises

Less dense than cooler fluid

Heat transfer in a vacuum

Radiation

Thermal conductor

Material that allows heat to pass easily

Insulator

Material that reduces heat transfer

Conduction in metals explanation

Free electrons transfer energy rapidly

Properties of metals

Good conductors, shiny, malleable, ductile, high melting point

Structure of metals

Positive ions in a sea of delocalised electrons

Electrical conductivity in metals

Free electrons carry charge

Radiation wave type

Infrared electromagnetic waves

Infrared location

Between visible light and microwaves

Best absorbers of radiation

Dark, matte surfaces

Best reflectors of radiation

Light, shiny surfaces

How insulation reduces heat loss

Traps air to reduce conduction and convection

Double glazing

Air gap reduces heat transfer

Vacuum flask conduction

Vacuum prevents conduction

Vacuum flask convection

No particles to move, so no convection

Vacuum flask radiation

Shiny surfaces reflect heat

Melting

Solid to liquid

Freezing

Liquid to solid

Evaporation

Liquid to gas at surface

Boiling

Liquid to gas throughout

Condensation

Gas to liquid

Sublimation

Solid to gas

Energy in change of state

Energy is used to break/form bonds

Why temperature stays constant

Energy changes state, not kinetic energy

Flat line on heating curve

Change of state

Melting point on graph

First flat section

Boiling point on graph

Second flat section

Energy during flat sections

Used to break bonds, not increase temperature

Why metal spoon feels colder

Conducts heat away faster than wood

Convection in boiling water

Hot water rises, cool water sinks creating currents

Reducing heat loss in house

Insulation, double glazing, thick walls

Why black surfaces used

Absorb more radiation

Heat transfer in boiling water

Conduction (pan), convection (water), radiation (heat)