PAL (IGCSE) – PHYSICS

Section 2 Thermal Physics

Thermal Physics

PAL (IGCSE) Single Science

Revision Book - Section 2

Name: ______

Teacher: ______


Syllabus Content______

Syllabus Details______

2.1 Simple kinetic molecular model of matter

2.1 (a) States of matter

Core

• State the distinguishing properties of solids, liquids and gases

2.1 (b) Molecular model

Core

• Describe qualitatively the molecular structure of solids, liquids and gases

• Interpret the temperature of a gas in terms of the motion of its molecules


• Describe qualitatively the pressure of a gas in terms of the motion of its molecules

• Describe qualitatively the effect of a change of temperature on the pressure of a gas at constant volume


• Show an understanding of the random motion of particles in a suspension as evidence for the kinetic molecular model of matter

• Describe this motion (sometimes known as Brownian motion) in terms of random molecular

Bombardment

·  Smoke (oil droplets) are seen to move randomly

·  This motion is evidence that the air particles are also moving randomly and colliding with the smoke droplets

·  The air particles cannot be seen but their motion can be understood by the smoke droplets which can be seen

Supplement

• Relate the properties of solids, liquids and gases to the forces and distances between molecules and to the motion of the molecules

Property / Solid / Liquid / Gas
Forces between particles / Strong bonds (strong forces) / Strong bonds (strong forces) / Essentially no bonding (v-weak forces)
Distances between particles / Fixed and short / Short but not fixed / Long
Motion of particles / Vibrating only / Vibrating and freely moving / Vibrating and freely moving

• Show an appreciation that massive particles may be moved by light, fast-moving molecules

2.1 (c) Evaporation

Core

• Describe evaporation in terms of the escape of more-energetic molecules from the surface of a liquid

• Relate evaporation to the consequent cooling

Supplement

• Demonstrate an understanding of how temperature, surface area and draught over a surface influence evaporation

Factor / Influence
Temperature / Increases evaporation as more particles have sufficient kinetic energy to “escape” the surface
Draught / Increases evaporation as “removes” high KE particles from above the surface of the liquid
Surface area / Increases evaporation as more surface for particles to “escape” from


2.1 (d) Pressure changes

Core

• Relate the change in volume of a gas to change in pressure applied to the gas at constant temperature

Supplement

• Recall and use the equation pV = constant at constant temperature

2.2 Thermal properties

2.2 (a) Thermal expansion of solids, liquids and gases

Core

• Describe qualitatively the thermal expansion of solids, liquids and gases

Solids

·  As the temperature increases the bonds in the solid vibrate more

·  The average separation between particles increases and so the bulk solid expands

Liquids

·  As the temperature increases the motion of the particles increase and so the kinetic energy

·  The average separation between the particles increases so the volume of the bulk liquid increases

Gases

·  The volume / dimensions of a gas are fixed by the container

·  As the temperature increases the motion of the particles increase and so the kinetic energy

·  The particles will collide with the container with more force and more often

·  If the container dimensions are free to change the volume will increase

• Identify and explain some of the everyday applications and consequences of thermal expansion

State / Application / Consequence
Solid / Railway lines
Jam jar lids / Railway lines to space to expand at the end of the line
If heated can be removed more easily
Liquid / In thermometers / As the liquid expands on heating this property can be used to measure temperature
Gas / Car tyres / After a long journey the pressure in your car tyres will increase as they become hot when driving

• Describe qualitatively the effect of a change of temperature on the volume of a gas at constant pressure

Supplement

• Show an appreciation of the relative order of magnitude of the expansion of solids, liquids and gases

State / Order of magnitude of expansion
Solid / Small
Liquid / Small
Gas / Big

2.2 (b) Measurement of temperature

Core

• Appreciate how a physical property that varies with temperature may be used for the measurement of temperature, and state examples of such properties

Physics property / Effect of temperature / Example
Volume of a liquid / Increases with increasing temperature / Mercury in glass thermometer
Resistance / Increases with temperature / Resistance thermometer

• Recognise the need for and identify fixed points

Fixed Points:

·  Used to calibrate thermometers

·  Boiling and melting water can be used as these 2 changes occur at fixed temperatures

·  The thermometer can be placed in boiling water to make the 100oC mark and then ice to make the 0oC mark

• Describe the structure and action of liquid-in-glass thermometers


Supplement

• Demonstrate understanding of sensitivity, range and linearity

• Describe the structure of a thermocouple and show understanding of its use for measuring high temperatures and those that vary rapidly

Thermocouple Thermometer

·  Consists of two metals connected as shown

·  When one junction between the two metal types is at a higher temperature than the other a voltage is produced

·  This voltage is dependent on the temperature difference between the junctions

·  They have a very large temperature range and can record temperatures very quickly

2.2 (c) Thermal capacity

Core

• Relate a rise in the temperature of a body to an increase in internal energy

Internal Energy = Random Kinetic Energy + Potential Energy of the particles

·  If temperature rises this indicates that the Kinetic energy of the particles has increased

·  If the kinetic energy of the particles increases so does the internal energy

• Show an understanding of the term thermal capacity

Supplement

• Describe an experiment to measure the specific heat capacity of a substance

·  Measure the temperature of a material before and after heating

·  Measure the energy input from heating by measuring the voltage, current and time

·  Remember that the block should be insulated as energy will be lost to the surroundings


2.2 (d) Melting and boiling

Core

• Describe melting and boiling in terms of energy input without a change in temperature

• State the meaning of melting point and boiling point

Melting point: The temperature at which solid and liquid phases both exist in equilibrium

Boiling point: The temperature at which a substance changes from a liquid to a gas throughout the bulk of the liquid

• Describe condensation and solidification

Condensation: As the kinetic energy of particles decreases the attractive forces between them “pull” them together into droplets. Bonds are formed.

Solidification: As the kinetic energy of particles decreases permanent bonds form between the particles so they are no longer able to move freely.

Supplement

• Distinguish between boiling and evaporation

Property / Boiling / Evaporation
Temperature / Only at the boiling point / At all temperatures
Location / Throughout the liquid / Only at the surface
Particles / All particles / Only the particles with sufficient kinetic energy
Temperature of liquid / Remains the same / Reduces

• Use the terms latent heat of vaporisation and latent heat of fusion and give a molecular interpretation of latent heat

LATENT HEAT OF VAPORISATION: Energy change associated with a substance

Boiling or Condensing

LATENT HEAT OF FUSION: Energy change associated with a substance

Melting or Solidifying

Molecular Interpretation: At a phase transition bonds are being broken or

formed. This gives an associated intake or release of energy.

• Describe an experiment to measure specific latent heats for steam and for ice

SPECIFIC LATENT HEAT OF STEAM

·  Take a volume of liquid to its boiling point

·  Measure the mass of the liquid

·  Boil the water for a fixed period and calculate the energy input by measuring the voltage and current for the heater

·  Record the mass of the liquid after heating and calculate the mass turned to a gas

·  SPECIFIC LATENT HEAT OF ICE

·  Heat the ice until it starts to melt

·  Capture the melted ice in the beaker on the balance

·  Heat for a fixed length of time and calculate the energy input by measuring the voltage and current supplied to the heater

·  Measure the mass of water melted in that period

2.3 Transfer of thermal energy

2.3 (a) Conduction

Core

• Describe experiments to demonstrate the properties of good and bad conductors of heat

·  Coins or other objects can be attached to a object to be tested

·  One end of the object is then heated

·  The ability of the object to conduct heat can be judged by how quickly the wax melts and so coins are released


Supplement

• Give a simple molecular account of heat transfer in solids

2.3 (b) Convection

Core

• Relate convection in fluids to density changes and describe experiments to illustrate convection

2.3 (c) Radiation

Core

• Identify infra-red radiation as part of the electromagnetic spectrum

Supplement

• Describe experiments to show the properties of good and bad emitters and good and bad absorbers of infra-red radiation

PROPERTIES OF ABSORBERS PROPERTIES OF EMMITERS

2.3 (d) Consequences of energy transfer

Core

• Identify and explain some of the everyday applications and consequences of conduction, convection and radiation

Energy Transfer / Applications / Consequences
Conduction / Saucepan or wok / Made of copper or other good conductors
Convection / Air conditioner / Normally placed on the ceiling as cold air drops
Radiation / Paint / In hot climates houses are painted white

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