THERMAL PHYSICS & KINETIC THEORY

Briefly describe/discuss the caloric theory of heat (from the 18th century)

The caloric theory said that heat is a kind of invisible fluid called "caloric" that flows from hot objects to cold ones. People thought that when something got hotter, it had more caloric, and when it cooled down, it lost caloric.

Explain how Count Rumford’s cannon boring experiment proved the caloric theory to be wrong

In the caloric theory, people believed heat (caloric) was like a substance stored inside objects.
So if you kept making something hot (like the cannon), it should eventually run out of "caloric" — like using up water in a bottle.
But in Rumford’s experiment, the cannon kept getting hot as long as the drill kept turning, meaning there was no "caloric" being used up — heat was being created by the motion instead.

What was the caloric theory replaced by?

The caloric theory was replaced by the kinetic theory of heat.

Briefly describe/discuss the Kinetic Theory of Heat

The kinetic theory of heat states that heat is the result of the motion of particles in matter. The faster they move, the hotter the object feels, and the slower they move, the cooler it feels.

Discuss the role of Joule’s experiments in establishing the principle of conservation of energy

Joule’s experiments showed that mechanical work (like stirring water) could produce heat.
He found that the more he stirred, the hotter the water got, and the amount of work done always matched the amount of heat produced.
This proved that energy wasn’t disappearing or being created — it was just changing from one form (movement) into another (heat).
This idea helped to establish the principle of conservation of energy, which says energy cannot be created or destroyed, only changed.

What is temperature?

The degree of hotness of a body. It is a measure of the average kinetic energy of the particles in a substance, indicating how fast they are moving.

Thermal energy always moves from an object with a ______ higher to an object with a _______ temperature

higher, lower

Two commonly used units for temperature are

Celsius and Fahrenheit

Temperature in Kelvin = ____ + Temperature in _____

273, Celsius

What is a thermometric property?

A physical property that changes with temperature, used to measure temperature.

Identify 3 physical properties that vary with temperature

Volume, Pressure, emf, Electrical Resistance

The SI unit for temperature is?

Kelvin

State the lower fixed point on the celsius scale

The freezing point of water, defined as 0 degrees Celsius.

What is the upper fixed point on the celsius scale?

The boiling point of water, defined as 100 degrees Celsius.

What type of thermometer is this?

A thermocouple thermometer

List 3 types of thermometers

• Clinical Thermometers

• Thermocouples

• Laboratory Thermometer

• Infrared Thermometers

The scale on the laboratory thermometer is positioned really close to the bore to prevent _____ ____ when reading it

parallax error

What is the advantage of using mercury in a liquid-in-glass thermometer?

Mercury is a metal so it has a high conductivity and a low specific heat capacity. This means its temperature quickly adjusts to the temperature it is measuring.

State 2 disadvantages of using a mercury thermometer

• Mercury is toxic and therefore it is hazardous

• Not suitable for cold temperatures

• It is expensive

The scale of a clinical thermometer is typically?

between 35 °C and 42 °C

What is the purpose of the constriction in a clinical thermometer?

The constriction in a clinical thermometer prevents the mercury from falling back into the bulb when the thermometer is removed from the patient's mouth, allowing for an accurate reading.

Intervals on the scale of the clinical thermometer are ____ degrees celsius

0.1

List TWO advantages of using a thermocouple thermometer

1. Fast response time.

2. Wide temperature range.

3. Since it is electrical, it can be connected to digital displays and computer systems.

State a disadvantage of using a thermocouple thermometer.

They can be more expensive than traditional thermometers.

Large temperature differences produce only small changes in emf. It is therefore not useful for detecting small changes in temperature.

Describe the composition of particles in a solid

Particles in a solid are tightly packed together in a fixed arrangement, resulting in a definite shape and volume. They vibrate in place but do not move freely, which gives solids their rigidity.

Describe the composition of particles in a liquid

Particles in a liquid are close together but not in a fixed arrangement, allowing them to slide past one another. This gives liquids a definite volume but no definite shape, adapting to the container they are in.

_____ and _____ are not easily compressed while _____ are easily compressed

Liquids and Gases, Gases

In terms of thermal expansion, explain why bubbles form in boiling water

The air expands when heated, producing bubbles in the water. As the water reaches its boiling point, the increase in temperature causes the water molecules to gain kinetic energy, leading to a phase change from liquid to gas, creating steam bubbles.

Explain how thermal expansion takes place in a bimetallic strip

When heated, one metal expands more than the other, causing the strip to bend. This bending effect is used in applications like thermostats to measure temperature changes.

Explain why a roof can creak when heated by the sun

When the roof material is heated by the sun, it expands. This expansion can cause stress at joints or connections, leading to creaking sounds as the materials shift.

How is a bimetallic strip used in a fire alarm?

A bimetallic strip in a fire alarm bends when heated, triggering a switch that activates the alarm. This mechanism allows for an automatic response to temperature changes associated with fire.

State 2 systems that a bimetallic strip can be used in

• Thermostats

• Fire alarms.

State Boyle’s Law

For a given mass of gas at constant temperature, the pressure of the gas is inversely proportional to its volume.

(PV=constant) State the law that this formula corresponds to

Boyle's Law

What is the formula for the combined gas law?

P1V1/T1 = P2V2/T2

Identify this law

For a fixed mass of gas at constant pressure, the volume is directly proportional to its absolute temperature.

Charles's Law

40 cm³ of an ideal gas at a temperature of 27 degrees c is heated to 227 degrees c in a freely expandable vessel. Determine the new volume of the gas.

Using Charles's Law, the new volume is 80 cm³.

What is ‘heat capacity’?

Heat capacity is the amount of heat needed to change the temperature of a substance by one degree celsius/kelvin

Distinguish between ‘heat capacity’ and ‘specific heat capacity’?

Heat capacity is the amount of heat energy needed to change the temperature of a substance by one degree celsius/kelvin, while specific heat capacity is the amount of heat energy needed to change the temperature of a substance by one degree celsius/kelvin per unit mass (1kg)

State the formula that relates heat capacity and specfic heat capacity

Heat capacity (C) = specific heat capacity (c) × mass (m)

C=mc

What is the common formula used to calculate the heat energy used during heat transfer

Q = mcΔT

E = mcΔT

Where, E/Q = heat energy, m = mass, c = specific heat capacity, ΔT = change in temperature

State 2 methods that can be used to find the specific heat capacity of metals and liquids

• Electrical Method

• Method of Mixtures

What is the unit for specific heat capacity?

joules per kilogram per degree Celsius (J/(kg·°C).

Describe how the specific heat capacity of a liquid can be found by the electrical method

1. Measure the mass and initial temp of the liquid

2. Then apply a known electrical current to heat it, measuring the temperature change over time.

3. Use the formula IVt = m (change in temp) to find the specific heat capacity

A graph of increasing temperature against time is known as a?

heating curve.

What is latent heat?

The energy needed to change the state of a substance without a change in its temperature

What is the specific latent heat of vaporization of a substance?

It is the energy required to change the state of a unit mass (1kg) of a substance from a liquid to a gas.

What is the specific latent heat of fusion of a substance?

It is the energy required to change the state of a unit mass (1kg) of a substance from a solid to a liquid.

Describe how the specific latent heat of fusion of ice can be found using an electrical method.

By measuring the amount of electric current and the time it is applied to an ice sample, the heat energy used to melt the ice can be calculated. Dividing this energy by the mass of the ice gives the specific latent heat of fusion.

IVt = m(of water) * latent heat of fusion

Differentiate between evaporation and boiling

Evaporation is the escape of molecules from the SURFACE of a liquid

Boiling is the escape of molecules WITHIN the body of a liquid and occurs only at a particular temperature for a given pressure.

What is conduction?

What is convection?

What is radiation?

Describe the characteristics of a surface that is a good conductor of heat

Describe the characteristics of a surface that is a poor conductor of heat

How does the design of a vacuum flask initiate or prevent conduction,convection and radiation?

Explain how global warming takes place (greenhouse effect)