# Thermal Physics (Due : Friday 10/6)

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Thermal Physics (Due : Friday 10/6)

## 1. Simple Kinetic Molecular Model of Matter (Zerlynde (the king), Sydny (the jester), Shahira (the peasant), Bryan (the stable boy), Shaun (the knight), Jun An (the sorcerer)

### 1.1. Kinetic Theory - Sydny

1.1.1. Basic Assumptions of the Kinetic Theory - zerlynde

1.1.1.1. 1. The volume occupied by the individual particles of a gas is negligible compared to the volume of the gas itself.

1.1.1.2. 2. The particles of an ideal gas exert no attractive forces on each other or on their surroundings.

1.1.2. Matter consists of large number of small particles (atoms or molecules)

1.1.3. Separation between particles are cause by the intermolecular forces. The particles attract each other strongly when close, but the attractions weaken if they move further apart

1.1.4. Particles are in constant motion. They collide and exchange energy. The temperature of a matter is the result of the average kinetic energy of particles.

### 1.2. Properties of:

1.2.1. Solid - Sydny

1.2.1.1. 1. The molecules are very close together and arranged in a regular pattern (held in place by strong intermolecular bonds)

1.2.1.2. 2. The molecules vibrate about fixed positions; have a fixed shape and volume

1.2.2. Liquid (Shahira)

1.2.2.1. 1. The molecules are still close together (no gaps) but are no longer arranged in a regular pattern

1.2.2.2. 2. The molecules are able to slide past each other; they take the shape of their container and have a fixed volume.

1.2.2.3. 3. When temperature is increased, the particles in a liquid gain more kinetic energy, move quicker and are able to escape from the surface of the liquid.

1.2.2.4. 4. Liquid pressure increases with depth (Jun An)

1.2.2.4.1. formula for liquid pressure= p (density of liquid) x g (acceleration of gravity) x h (height/ depth of liquid).

1.2.2.4.2. Denser liquids such as oil will exert more pressure on a submerged object compared to a less dense liquid like water.

1.2.3. Gas - zerlynde

1.2.3.1. 1. The molecules constantly collide with each other at high speeds, creating gas pressure. (Shahira)

1.2.3.1.1. Pressure = Force/Area

1.2.3.1.2. When gas particles collide with a wall, a change in momentum is produced.

1.2.3.2. 2. When temperature is increased, the gas molecules collide with each other more frequently, increasing pressure. (Jun An)

1.2.3.2.1. Pressure is inversely proportional to volume, as stated by Boyle's law.

1.2.3.2.2. p ∝ 1/v, therefore p x v = 1

1.2.3.3. 3. The molecules are far apart and not arranged in a regular pattern. (Jun An)

1.2.3.4. 4. No fixed shape, no fixed volume, can be compressed, unlike liquids (who can be compressed lightly) and solids. (Jun An)

### 1.4. Explanation - zerlynde

1.4.1. Matter is made out of constantly moving particles; all matter occupies physical space.

1.4.2. All particles have energy, which depends on the temperature the sample of matter is in

1.4.2.1. The state of matter of a substance can change if the intermolecular energy is enough to overcome/strengthen the forces of attraction between the particles of the substance.

1.4.3. Brownian motion occurs as a result of the constant movement of particles, and is described as the erratic movement of particles.

1.4.3.1. Particles move in a zig-zag motion because they are being hit by other tiny invisible particles

## 2. Thermal Properties & Temperature (Alex, Aidan, Hu Jay, Ariel, Kirthiga, Haelee, Sewon)

### 2.1. Thermal Expansion ( Kirthiga)

2.1.1. When something is heated it expands because the molecules take up more space :

2.1.1.1. When a gas is heated, the molecules move faster and further apart, so the relative order of magnitude of the expansiojn is the greatest.

2.1.2. Ice uniquely does not follow this theoretical concept of being heated and expanding. Ice takes up more space than water, where normally a liquid cooled will take up less space. Instead, water molecules link up to form an organised crystal structure that takes up more space than water. (Alex)

2.1.2.1. When a solid is heated, the molecules vibrate more but stay in place, so the relative order of magnitude of the expansion is small.

2.1.2.2. Applications and consequences of thermal expansion include:

2.1.2.2.1. The liquid in a thermometer expands with temperature and rises up the glass

2.1.2.2.2. Railway tracks having small gaps so that they don't buckle when they expand

2.1.3. Thermostats use the property of thermal expansion where a material expands in a circuit to trigger the mechanism

### 2.2. Specific Latent Heat (Kirthiga)

2.2.1. Definition of Latent Heat of Fusion - The amount of energy that grants molecules the ability to overcome their intermolecular forces. (Alex)

2.2.1.1. Temperature does not change when latent heat of fusion is occurring. Kinetic energy is transferred to particles to overcome intermolecular forces instead of being registered as temperature. (Alex)

2.2.1.2. When a liquid is heated, it expands for the same reason as a solid but the intermolecular forces are less so it expands more. (Hu Jay)

2.2.1.3. Pressure in a container occurs as a result of thermal expansion from substances. According to Gay-Lusaac's law, when the volume of a container is constant, pressure increases in a direct proportion along with temperature. (Alex)

2.2.2. The amount of heat required to change the phase of 1 kg of substance at a constant temperature. Measured in Jkg-1.( Kirthiga)

2.2.2.1. The amount of heat required to convert 1 kg of a solid into liquid at the constant temperature (Kirthiga )

2.2.2.1.1. Specific latent heat of fusion

2.2.2.2. The amount of heat required to convert 1 kg of a liquid into gas at the constant temperature ( Kirthiga )

2.2.2.2.1. Specific latent heat of vaporisation

2.2.3. When a body changes state, energy goes towards making the molecules move free from each other rather than increasing their kinetic energy. ( Kirthiga )

2.2.3.1. Graph showing the temperature of ice with time when energy is put in at a constant rate: ( Kirthiga )

2.2.4. energy = mass x specific latent heat (Kirthiga)

### 2.3. Heat Capacity (Haelee)

2.3.1. Specific Heat Capacity

2.3.1.1. The amount of heat required to increase the temperature of 1 kg of substance by 1 °C (or K). C=Q/mΔT

2.3.1.1.1. The term specific refers to per unit mass.Measured in J/kg °C or J/kg K. Only depends on the type of material of object.

2.3.1.1.2. The specific heat capacity of water is 4200 J/kg °C and that of soil is about 800 J/kg °C. Temperature of the sea rises and falls more slowly than that of the land. Water needs 5 times the amount of heat to raise its temperature by 1 °C.

2.3.1.1.3. Water is used in cooling engines and in the radiators of central heating systems because of its high heat capacity, cheapness and availability.

2.3.2. The amount of heat required to increase the temperature of a substance by 1 °C (or 1 K). C= Q/ΔT

2.3.3. Measured in J/°C or J/K. Depends on mass and type of material.

### 2.4. Measuring Temperature

2.4.1. A physical property that varies with temperature can be used, such as thermometers: (by ariel)

2.4.1.1. Liquid-in-glass

2.4.1.1.1. When the glass bulb is heated, the liquid expands upwards in the capillary tube.

2.4.1.1.2. Examples: Mercury freezes at -39°C and boils at 357°C (higher temperatures), whilst alcohol freezes at -115°C and boils at 78°C (lower temperatures)

2.4.1.2. Thermistor

2.4.1.2.1. Invented by Samuel Rubent, this type of thermometer relies on the change in its resistance and electrical conductivity with temperature change. The higher the temperature, the higher the current that flows from a battery --> higher reading on the meter.

2.4.1.2.2. Range: -5°C to 70°C

2.4.1.3. Thermocouple

2.4.1.3.1. This thermometer contains 2 different metals joined to form 2 junctions, which allows a temperature difference causing a voltage that initiates the flow of current. Higher temperature difference = higher current.

2.4.1.3.2. Normally used for rapid changes in high temperature, it ranges from -200°C to 1100°C.

2.4.1.4. Infrared

2.4.1.4.1. Temperature of the object can be detected by the amount of thermal radiation emitted.

2.4.1.4.2. Example: Non-contact thermometers

2.4.2. Properties of Thermometers (by ariel)

2.4.2.1. Linearity

2.4.2.1.1. Measures the proportionality of change the physical property. A thermometer is considered linear if its temperature readings change proportionally with the length of the mercury column. ( Kirthiga)

2.4.2.2. Sensitivity

2.4.2.2.1. Change in length of mercury column per unit degree change in temperature. It depends on:

2.4.2.3. Responsiveness

2.4.2.3.1. The speed to obtain a reading. Depends on the thickness of the glass bulb, therefore thinner = more sensitive. (Kirthiga)

2.4.2.4. Range

2.4.2.4.1. The range of a thermometer defines the total range of temperature a thermometer is able to measure. Influenced by: • Melting and boiling point of substance in thermometer • Thermal expansion rate of substance in thermometer • Length of capillary tube (Alex)

2.4.2.5. Linearity

2.4.2.5.1. Linearity is when a given change in temperature causes the same change in length ( Kirthiga)

2.4.3. Calibration and Accuracy (Kirthiga)

2.4.3.1. Fixed points are used to calibrate thermometers. For example, the fixed points of the celsius scale are the melting point and the boiling point of water

2.4.4. Interesting Temperature Facts (by AIdan)

2.4.4.1. Absolute zero is the coldest theoretical temperature. Reaching this temperature substance does not possess any heat energy. It has been defined as zero Kelvin (0 Kelvin) which is found to be equivalent to -273.16 degrees Celsius and -459.69 degrees Fahrenheit.

2.4.4.2. The average surface temperature of Sun is 5,600 Kelvin

2.4.4.3. 57.8 °C (136 °F) is the hottest temperature ever recorded on Earth. It was recorded on September 13, 1922 in Al ‘Aziziyah located in Libya.

2.4.4.4. −89.2 °C (−128.6 °F) is the coldest temperature ever recorded on Earth. It was recorded at Vostok Station located in Antarctica on July 21, 1983.

2.4.4.5. Fahrenheit and Celsius are equal at -40 degrees

2.4.5. Units of Temperature (Alex)

2.4.5.1. Celsius (Alex)

2.4.5.1.1. A measurement where 0ºC is the freezing point of water and 100ºC is the boiling point of water. (Alex)

2.4.5.2. Fahrenheit (Alex)

2.4.5.2.1. Another everyday unit of temperature where 32ºF and 212ºF is the boiling point of water. (Alex)

2.4.5.3. Kelvin (Alex)

2.4.5.3.1. SI unit of temperature. 0 Kelvin is recognised as the lowest possible temperature in matter. Kelvin is used in many physics formulas as a standard unit in order to obtain (Alex)

## 3. Thermal Processes (Nicholas, Daniel, Chloe, Isabelle, Sewon)

### 3.1. Conduction

3.1.1. Definition

3.1.1.1. The process by thermal energy (heat) is transferred from one atom to another within an object by direct contact (chloe)

3.1.2. Thermal Conductors & Insulators (chloe)

3.1.2.1. Conductors

3.1.2.1.1. Metals are the best conductors of heat

3.1.2.2. Insulators

3.1.2.2.1. Non-metals and most liquids tend to be insulators

3.1.2.2.2. Gases are the worst conductor

3.1.2.2.3. Many are insulators because they contain tiny pockets of trapped air

3.1.3. How materials conduct (chloe)

3.1.3.1. How metals conducts

3.1.3.1.1. Electrons in metal atoms are 'loose' and free to drift between metals

3.1.3.1.2. When heated, these free electrons speed up. As they move randomly within the metal, they collide with atoms and vibrate faster

3.1.3.2. How all materials conduct except metals

3.1.3.2.1. When heated, particles move faster, pushing neighbouring particles, speeding those up too

3.1.4. More thermal energy is transferred every second if: (sewon)

3.1.4.1. 1. The temperature difference across the ends of the bar is increased

3.1.4.2. 2. The cross-sectional area of the bar is increased

3.1.4.3. 3. The length of the bar is reduced

### 3.2. Convection

3.2.1. Definition

3.2.1.1. When a gas or liquid is heated, warmer molecules rise to the top and displace denser, cooler molecules, which sink to the bottom. These cooler molecules are also heated and rise and the cycle starts over. This is a convection current. (Nicholas

3.2.2. Examples in nature (Nicholas)

3.2.2.1. In a fire, heated smoke particles rise up, so one must stay low to avoid smoke particles.

3.2.2.2. In the day, coastal winds are blown from the sea as it is cooler than the land during the day ; they rise when in contact with land because the land heats up faster during the day. At night, coastal winds blow from the land as air sinks towards the land because the land cools faster at night ; the winds rise when it reaches the sea as it is warmer.

3.2.2.3. Birds detect where the warm air rises during the day so that they can use it to lift up and fly.

3.2.3. Convection at Home(isabelle)

3.2.3.1. Hot water system

3.2.3.1.1. In a large storage tank, water is heated by a coil of copper pipe: hot water from boiler flows through this & is recirculated by a pump. In the tank, heated water rises to the top by convection. The tank is insulated to reduce thermal energy losses by conduction and convection.

3.2.3.2. Room heating

3.2.3.2.1. Warm air rising above a convector heater/radiator carries thermal energy all around the room. However the coolest air is always around your feet.

3.2.3.3. Refrigerator

3.2.3.3.1. Cold air sinks below the freezer compartment. This sets up a circulating current of air which cools all the food in the refrigerator.

3.3.1. Energy in the form of electromagnetic waves from the sun. This includes infrared and light waves. Things that absorb them heat up so they are often referred to as thermal radiation. (Nicholas)

3.3.1.1. Thermal radiation is a mixture of different wavelengths. Warm objects radiates infrared. If they become hotter they will remit shorter wavelengths, including light. (Nicholas)

3.3.2. Emitters (Nicholas and isabelle)

3.3.2.1. Metals are better emitters of radiation than other materials, so they cool down more quickly.

3.3.2.2. Darker shades emit radiation better than most colours. Matt Black is the best whereas silver is the worst.

3.3.2.3. Good emitters are also good absorbers.

3.3.3. Absorbers (Nicholas and isabelle)

3.3.3.1. Darker shades absorb radiation better than lighter shades. Matt black is the best whereas silver is the worst.

3.3.3.2. Silver/white surfaces reflect most of the thermal radiation away. This is why houses in hot, sunny countries are painted white to keep them cool inside.

3.3.4. Greenhouse Effect (Nicholas and Danial)

3.3.4.1. The Earth's atmosphere traps radiation emitted by the sun because some gases (water vapour, methane, carbon dioxide) absorb energy at certain wavelengths and reflect it back. This keeps Earth's temperature constant and never too hot or cold.

3.3.4.2. The glass in a greenhouse lets the sun's radiation in, which heats the air inside, but prevents it from escaping, so the inside stays heated.

3.3.5. Uses (Nicholas and Danial)

3.3.5.1. Solar Panels

3.3.5.1.1. Networks of water pipes can be painted black to absorb more radiation for heating.