Thermal Physics
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Questions and Answers

What does the mean square speed of gas molecules signify?

  • The total speed of a single molecule
  • The mean of the square speeds of the gas molecules (correct)
  • The average speed of all molecules in a gas
  • The square root of the speeds of all molecules

An ideal gas has potential energy equal to the sum of kinetic energies of its particles.

False (B)

What is the formula that relates pressure, volume, and the mean square speed of gas molecules?

pV = (3/2)Nmc^2

In the equation $c^2 = u^2 + v^2 + w^2$, the variables u, v, and w represent the __________ components of a molecule’s velocity.

<p>spatial</p> Signup and view all the answers

Match the following concepts with their descriptions:

<p>Ideal Gas = No intermolecular forces, perfectly elastic collisions Mean Square Speed = The average of the squares of speeds of gas molecules Brownian Motion = Random motion of particles suspended in a fluid Kinetic Theory = Theory explaining gas behavior based on particle motion</p> Signup and view all the answers

Which of the following statements about an ideal gas is correct?

<p>Ideal gases follow the gas laws perfectly. (B)</p> Signup and view all the answers

What role does the cube's volume (V) play in the pressure equation for gas particles?

<p>Volume is used to relate the total pressure to the kinetic energy of the gas molecules.</p> Signup and view all the answers

The mean square speed in all three dimensions is assumed to be different for an ideal gas.

<p>False (B)</p> Signup and view all the answers

According to Boyle's Law, how do pressure and volume relate when temperature is constant?

<p>Pressure and volume are inversely proportional. (D)</p> Signup and view all the answers

Charles' Law states that when pressure is constant, volume is inversely proportional to absolute temperature.

<p>False (B)</p> Signup and view all the answers

What is the equation for the ideal gas law?

<p>pV = nRT</p> Signup and view all the answers

1 mole of a substance contains _____ atoms/molecules.

<p>6.02 × 10^23</p> Signup and view all the answers

Match the gas law with its respective relationship:

<p>Boyle's Law = Pressure and volume are inversely proportional. Charles' Law = Volume is directly proportional to absolute temperature. The Pressure Law = Pressure is directly proportional to absolute temperature. Ideal Gas Law = pV = nRT.</p> Signup and view all the answers

What is the specific heat capacity of water?

<p>4200 J/kg°C (C)</p> Signup and view all the answers

Absolute zero is defined as 0°C.

<p>False (B)</p> Signup and view all the answers

To convert Celsius to Kelvin, you use the formula _____ = C + 273.

<p>K</p> Signup and view all the answers

According to Boyle's law, what happens to the pressure of a gas when its volume increases at constant temperature?

<p>Pressure decreases (D)</p> Signup and view all the answers

Charles's law indicates that volume and pressure are directly proportional at constant temperature.

<p>False (B)</p> Signup and view all the answers

What is the formula used to calculate work done on a gas?

<p>W = pΔV</p> Signup and view all the answers

Brownian motion is the __________ motion of larger particles in a fluid caused by collisions with surrounding particles.

<p>random</p> Signup and view all the answers

Which statement represents the relationship described by Charles's law?

<p>Volume increases as temperature increases (A)</p> Signup and view all the answers

Match the following gas laws with their descriptions:

<p>Boyle's Law = Pressure is inversely proportional to volume at constant temperature Charles's Law = Volume is directly proportional to temperature at constant pressure Ideal Gas Law = Relates pressure, volume, and temperature to the number of molecules Work done on gas = Calculated using the formula W = pΔV</p> Signup and view all the answers

The constant used to relate temperature and energy in terms of gas is known as the __________ constant.

<p>Boltzmann</p> Signup and view all the answers

What phenomenon provides evidence for the existence of atoms and molecules through the random motion of larger particles?

<p>Brownian motion</p> Signup and view all the answers

Flashcards

Mean square speed

The average of the squares of the speeds of gas molecules.

Ideal gas

A gas where molecules only interact through perfectly elastic collisions, no intermolecular forces.

Internal energy of an ideal gas

The sum of the kinetic energies of all its particles.

Pressure of a gas (simplified)

Total pressure is the sum of individual pressures from each molecule in the gas.

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c^2 equation

c^2 = u^2 + v^2 + w^2 where c is the overall speed and u,v,w are speeds in the three dimensions.

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Simplified pressure equation

pV = 1/3 * N * m * c^2 (or equivalent forms)

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u^2 = v^2 = w^2

Assuming random motion, the mean square speed is equal for each direction in space.

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pV = 3/2 NkT

A key equation connecting pressure (P), volume (V), number of particles (Nk), and temperature (T) in an ideal gas.

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Boyle's Law

At constant temperature, the pressure of a gas is inversely proportional to its volume. This means if you increase the pressure, the volume decreases proportionally and vice versa.

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Charles' Law

At constant pressure, the volume of a gas is directly proportional to its absolute temperature. This means if you increase the temperature, the volume increases proportionally and vice versa.

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Pressure Law

At constant volume, the pressure of a gas is directly proportional to its absolute temperature. This means if you increase the temperature, the pressure increases proportionally and vice versa.

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Absolute Zero

The lowest possible temperature, where particles have no kinetic energy. It is equivalent to 0 Kelvin or -273°C.

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Kelvin Scale

The absolute temperature scale, where 0 Kelvin is absolute zero. To convert Celsius to Kelvin, add 273.

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Ideal Gas Equation

pV = nRT, where p is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is the absolute temperature.

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Moles

A unit of measurement for the amount of substance. 1 mole contains Avogadro's number (6.02 x 10^23) of particles.

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Avogadro Constant

The number of particles in one mole of a substance, approximately 6.02 x 10^23.

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Molar Mass

The mass (in grams) of one mole of a substance. It is found by adding the masses of all the atoms within a molecule of the substance.

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Work Done on a Gas

The work done on a gas to change its volume at constant pressure is calculated as: Work done = pΔV, where p is the pressure and ΔV is the change in volume. This work is usually done through transferring heat energy into the gas

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Brownian Motion

The random movement of larger particles in a fluid caused by collisions with surrounding particles, observable under a microscope. It provided evidence for the existence of atoms and molecules.

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How does temperature affect gas volume?

When a gas is heated, its molecules gain kinetic energy, moving faster. This leads to more frequent and stronger collisions with the container walls, increasing pressure. To keep pressure constant, the volume needs to increase, allowing the molecules to spread out.

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Why does pressure decrease with increasing volume?

When the volume of a container increases, molecules have a larger space to move. Collisions become less frequent, and the force exerted on the container walls decreases, resulting in lower pressure.

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How does increasing the volume of gas affect collisions?

Increasing volume means the average distance between gas molecules increases. This leads to fewer collisions with the container walls because they spend less time close together.

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Study Notes

Thermal Physics

  • Internal Energy: The sum of all kinetic and potential energies of particles in a body. Randomly distributed. Increased by work or temperature change.

  • Internal Energy Transfer: Can increase by doing work on the system or increasing its temperature.

  • Changing State: Changing the state of a substance (e.g., solid to liquid) changes its internal energy (potential energy). Kinetic energy remains constant during change of state.

  • Specific Heat Capacity: The energy required to increase the temperature of 1 kg of a substance by 1 °C (or 1 K). Formula: Q = mcΔT, where Q is energy, m is mass, c is specific heat capacity, and ΔT is the change in temperature.

  • Specific Latent Heat: Energy required to change the state of 1 kg of a substance without changing its temperature. Two types: latent heat of fusion (solid to liquid) and latent heat of vaporization (liquid to gas). Formula: Q = ml, where Q is energy, m is mass, and l is the specific latent heat.

Ideal Gases

  • Gas Laws: Empirical relationships between pressure (p), volume (V), and temperature (T). Used for fixed mass of gas.

    • Boyle's Law: Pressure and volume are inversely proportional at constant temperature (pV = constant).

    • Charles' Law: Volume is directly proportional to absolute temperature at constant pressure (V/T = constant).

    • Pressure Law: Pressure is directly proportional to absolute temperature at constant volume (p/T = constant).

  • Absolute Temperature Scale (Kelvin): Measured in kelvin (K), with 0 K being absolute zero (no kinetic energy). Formula: K = C + 273, where K is Kelvin and C is Celsius.

  • Ideal Gas Equation: Combines all gas laws into one equation: pV = nRT ,where p is pressure, V is volume, n is number of moles, R is the ideal gas constant, and T is the absolute temperature.

Molecular Kinetic Theory

  • Brownian Motion: The random motion of tiny particles (e.g., dust particles in air) caused by collisions with surrounding molecules. Provides evidence for the existence of atoms and molecules.

  • Molecular Model for Gas Laws: Explaining gas laws using molecular motion concepts.

    • Boyle's Law: Increased volume means less frequent collisions, decreasing pressure.
    • Charles' Law: Higher temperature means faster molecular movement, leading to greater volume.
    • Pressure Law: Increased temperature means increased collisions and increased pressure (at constant volume).

  • Assumptions of the Kinetic Theory Model:

    • No intermolecular forces
    • Negligible duration of collisions
    • Random motion
    • Perfectly elastic collisions
    • Move in straight lines

  • Derivation of the Ideal Gas Equation: Calculated from the principles of momentum change and mean square speed of molecules.

  • Internal Energy in Gases: The internal energy only depends on the kinetic energy of the gas molecules.

  • Kinetic Energy of Gas Molecules: The equation: Ek = 3/2 kT per molecule. where Ek is the kinetic energy of the molecule, k is the Boltzmann constant, and T is the absolute temperature.

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AQA Physics A-level Thermal Physics Notes PDF

Description

Test your knowledge on thermal physics concepts such as internal energy, specific heat capacity, and latent heat. This quiz explores the principles governing temperature changes and state transitions of substances. Are you ready to challenge your understanding?

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