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Thermal effects - Callibration of thermometers

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Unit 5 – Thermal effects
5.01 Moving particles
The kinetic theory of matter
Solids, liquids and gases and their particles
How the properties of solids, liquids and gases depend on
the motion and arrangement of their particles (e.g.
molecules)
Brownian motion and why it occurs
The link between internal energy, moving particles
(molecules) and temperature
5.02 Temperature (1)
The link between internal energy and temperature
Measuring temperature: the principles
The link between temperature and the motion of particles
(e.g. molecules)
Thermocouple thermometers: how they work, and their
advantages
Unit 5 – Thermal effects
5.03 Temperature (2)
Defining a temperature scale: fixed points
Melting point and boiling point
The structure and action of a liquid-in-glass thermometer
Thermocouple thermometers: how they work and their
advantages
The sensitivity, range and linearity of a thermometer
5.04 Expanding solids and liquids
The thermal expansion of solids and liquids, its effects and
its uses
Comparing the expansions of solids, liquids and gases
Unit 5 – Thermal effects
5.05 Heating gases
How the pressure of a gas is caused by the motion of its
particles (molecules)
Why pressure increases with temperature for a gas at
constant volume
Why volume increases with temperature for a gas at
constant volume
Comparing the expansions of solids, liquids and gases
How gas pressure is caused by momentum changes of
particles (molecules)
Explaining why, when heated (at constant pressure), gases
expand much more than liquids and liquids more than solids
5.06 Heating gases
Good and poor thermal conductors
Why some materials are better thermal conductors than
others
Unit 5 – Thermal effects
• 5.05 Heating gases
• 5.06 Thermal conduction
• 5.07 Convection
• 5.08 Thermal radiation
• 5.09 Liquids and vapours
• 5.10 Specific heat capacity
• 5.11 Latent heat
5.01 Moving particles
Solids, liquids, and gases
5.01 Moving particles
Solids, liquids, and gases
5.01 Moving particles
Solids, liquids, and gases
5.01 Moving particles
Brownian motion: evidence for moving particles
In 1827, a botanist named Robert Brown observed the
random movement of particles in liquids.
Observation:
pollen grains wobbling and jiggling about in water.
Explanation:
the pollen grains are being bombarded by the molecules of
water around them
This movement is called Brownian
motion.
It proves that matter is made up of
tiny particles.
5.01 Moving particles
5.01 Moving particles
Brownian motion: evidence for moving particles
Brownian motion also explains how smoke particles
move about in air.
Observation:
Smoke particles wobble about in zig-zag paths.
Explanation:
Air particles are bumping
into the smoke particles.
5.01 Moving particles
Energy of particles
The particles in solids, liquids, and gases have kinetic
energy because they are moving.
Solids – low kinetic energy – vibrates about fixed position
Liquids – moderate kinetic energy – moves randomly
Gases – high kinetic energy – moves are high speed
The particles also have potential energy because
there are forces of attraction trying to hold them
together.
Solids – low potential energy – fixed position
Liquids – moderate potential energy – close together/ not
fixed and glide over one another
Gases – high potential energy – very far apart from one
another
5.01 Moving particles
Energy of particles
Internal energy = potential energy + kinetic energy of
all the particles in a substance
When:
Substances get hotter  particles move faster  internal
energy 
Substances get colder  particles move slower  internal
energy 
Hot substances transfer energy to
cold substances – called heat.
Hot substance loses internal energy.
Cold substance gains internal energy.
5.02 Temperature (1)
The Celsius scale
Temperature is a measure of hotness.
This measure is hotness comes from the average
kinetic energy per particle in a substance.
Hence:
1. Higher temperature = higher average kinetic energy per
particle
2. Lower temperature = lower average kinetic energy per
particle
Temperature is NOT the same as heat. Heat is a form
of energy but temperature is not energy.
5.02 Temperature (1)
The Celsius scale
Temperature is a measure of hotness.
The Celsius scale aka the Centigrade scale is very
commonly used.
Unit: degree Celsius (°C)
The Celsius scale has two fixed points:
1. The melting point of water: 0°C
2. The boiling point of water: 100°C
Practical activity 5.3 – Determining absolute zero
5.02 Temperature (1)
Absolute zero and the Kelvin scale
The lowest temperature in the
universe = –273°C
At this temperature, particles have
the lowest kinetic energy;and
move the slowest
This is why this temperature is
called absolute zero.
The Kelvin scale starts at absolute zero – 0K.
Temperature in Kelvin = Temperature in °C + 273
5.02 Temperature (1)
Thermometers
Temperature is measured using thermometers.
Liquid-in-glass thermometers
Glass bulb
contains liquid (alcohol or mercury)
thin glass:
1. increase sensitivity of thermometer – allow heat to enter and leave
quickly
Liquid in bulb
expands when temperature rises and pushes a thread of
liquid into the capillary tube.
thin tube:
1. increase sensitivity of thermometer – thread moves easily for a
small change in temperature
5.02 Temperature (1)
5.02 Temperature (1)
Thermometers
Thermocouple thermometer
Made up of:
1. Two different metals
2. Two different junctions – inserted into two substances of
different temperatures
3. A meter – converts potential difference into temperature
How it works:
1. Temperature difference causes a current to flow
 The higher the temperature difference, the greater the current flow.
 The greater the current flow, the greater the potential difference.
2. The meter
temperature.
converts
the
potential
difference
into
5.03 Temperature (2)
Fixing a temperature scale
To create a temperature scale, two standard temperatures
must be chosen i.e. two fixed points.
Calibrating an instrument means to put a scale on a
measuring instrument so that it gives accurate readings.
The fixed points chosen for the Celsius scale are: 0°C and
100°C.
Step 1:
Put the column into ice and measure the height of the increase in
liquid/ mercury.
Step 2:
Put the column into boiling water and measure the height of the
increase in liquid/ mercury.
Step 3:
Divide the distance between the two fixed points into 100 equal
divisions. Each division is called 1°C.
5.03 Temperature (2)
Liquid-in-glass thermometers
Liquids are used in thermometers because they
expand when heated.
This expansion causes them to move up the column
and give a reading.
Sensitivity
How far the liquid moves when heated
Smaller column/ tube width will increase sensitivity
Mercury expands less than alcohol – so the tube of a
mercury thermometer needs to be narrower to have same
sensitivity as a liquid-in-glass thermometer
Thicker glass/ bulb will reduce responsiveness because it
reduces heat absorption
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