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Physics: Thermal Physics - Kinetic Theory, Temperature, and Thermal Equilibrium

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Kinetic Theory of Matter: All matter is composed of tiny particles (atoms or molecules) that are in constant, random motion. The state of matter (solid, liquid, or gas) depends on the arrangement and the energy of these particles.

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Temperature (TT): Temperature is a measure of the average kinetic energy (EkE_k) of the particles in a substance. Higher temperature means particles move or vibrate faster.

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Thermal Energy: This is the total internal energy of an object, which includes the sum of the kinetic and potential energies of all its particles.

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Heat (QQ): Heat is the transfer of thermal energy from a substance at a higher temperature to a substance at a lower temperature.

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Thermal Equilibrium: A state where two or more objects in thermal contact reach the same temperature and there is no net flow of heat energy between them.

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The Kelvin Scale: An absolute temperature scale where 0 K0\text{ K} (Absolute Zero) represents the point at which molecular motion theoretically stops.

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Brownian Motion: The random movement of microscopic particles suspended in a fluid (liquid or gas) resulting from collisions with the fast-moving molecules of the fluid. This provides evidence for the Kinetic Theory.

📐Formulae

TK=TC+273.15T_{K} = T_{C} + 273.15

TC=TK−273.15T_{C} = T_{K} - 273.15

Ek∝TE_k \propto T

ΔT=Tfinal−Tinitial\Delta T = T_{final} - T_{initial}

💡Examples

Problem 1:

A scientist records the temperature of a liquid nitrogen sample as 77 K77\text{ K}. What is this temperature in degrees Celsius (∘C^\circ\text{C})?

Solution:

TC=77−273.15T_{C} = 77 - 273.15 TC=−196.15∘CT_{C} = -196.15^\circ\text{C}

Explanation:

To convert from Kelvin to Celsius, we subtract 273.15273.15 from the Kelvin value as per the standard conversion formula.

Problem 2:

An iron block at 90∘C90^\circ\text{C} is placed in contact with a copper block at 20∘C20^\circ\text{C}. Describe the flow of energy and the condition when they reach 55∘C55^\circ\text{C} each.

Solution:

Thermal energy flows from the iron block (90∘C90^\circ\text{C}) to the copper block (20∘C20^\circ\text{C}). When both reach 55∘C55^\circ\text{C}, they are in thermal equilibrium.

Explanation:

Heat always flows from a region of higher temperature to a region of lower temperature. Once the temperatures are equal, the net heat transfer becomes zero, achieving thermal equilibrium.

Problem 3:

If the temperature of a gas in a sealed container is increased from 300 K300\text{ K} to 600 K600\text{ K}, what happens to the average kinetic energy of the particles?

Solution:

The average kinetic energy (EkE_k) doubles.

Explanation:

According to the Kinetic Theory, the average kinetic energy of the particles is directly proportional to the absolute temperature (measured in Kelvin). Since the temperature doubled (300 K300\text{ K} to 600 K600\text{ K}), the average kinetic energy also doubles.