Thermodynamics in Edexcel A-Level Physics ***

What formula is used to calculate the energy required to change the temperature of a substance?

E = mcΔθ, where ΔE is energy required, m is mass, c is specific heat capacity, and Δθ is the change in temperature.

What is specific heat capacity (c)?

The amount of energy required to increase the temperature of 1 kg of a substance by 1 °C/1 K without changing its state.

What formula is used to calculate the energy required to change the state of a substance?

E = mL, where ΔE is energy required, L is specific latent heat, and m is mass.

What is specific latent heat (L)?

The amount of energy required to change the state of 1 kg of material without changing its temperature.

What are the two types of specific latent heat?

Specific latent heat of fusion (solid to liquid) and specific latent heat of vaporisation (liquid to gas).

What is the internal energy of a body?

The sum of all the kinetic and potential energies of all its particles.

What happens to the internal energy of a substance when its state changes?

The internal energy changes because the potential energy of the system changes, while the kinetic energy remains constant.

How do you set up equations for energy transfer in a closed system?

By equating the energy transfer in the water and the ice separately.

What is the significance of the internal energy being randomly distributed?

It indicates that the kinetic and potential energies of particles are not uniform but vary throughout the substance.

What does the formula E = mcΔθ represent in thermodynamics?

It represents the calculation of thermal energy transfer due to temperature change.

What does the formula E = mL represent in thermodynamics?

It represents the calculation of thermal energy transfer due to a change in state.

What is absolute zero in Celsius and Kelvin?

Absolute zero is -273°C, which is equivalent to 0 K.

What happens to particles at absolute zero?

At absolute zero, particles have no kinetic energy, and the volume and pressure of a gas are zero.

What is the relationship between Celsius and Kelvin temperatures?

A change of 1 K is equal to a change of 1°C, and the conversion formula is K = C + 273.

What is the equation relating average kinetic energy of molecules to temperature?

Average kinetic energy is given by the equation kT = (3/2)kT, where k is the Boltzmann constant and T is temperature in Kelvin.

How is the average kinetic energy of gas molecules related to temperature?

The average kinetic energy of gas molecules is directly proportional to the temperature in Kelvin.

What are the assumptions of the kinetic theory model?

1. No intermolecular forces act on the molecules. 2. Duration of collisions is negligible compared to time between collisions. 3. Molecules move randomly and experience perfectly elastic collisions. 4. Molecules follow Newton's laws. 5. Molecules move in straight lines between collisions.

How is the change in momentum of a gas molecule calculated during a collision?

The change in momentum is calculated as 2mu, where m is the mass of the molecule and u is its velocity.

What is the formula for the time between collisions of a molecule in a gas?

The time between collisions is given by t = (2l)/u, where l is the side length of the cube and u is the velocity.

How is pressure derived from the impulse of a gas molecule?

Pressure is derived by dividing the impulse (rate of change of momentum) by the area of one wall, leading to P = (1/3)(mu^2)/V, where V is the volume.

What is the mean square speed in the context of kinetic theory?

The mean square speed is the average of the squares of the speeds of gas molecules, used to estimate the total pressure.

What is the equation for total pressure in terms of mean square speed?

Total pressure P is given by P = (Nmu^2)/V, where N is the number of particles.

What does the kinetic theory model relate in a fixed mass of gas?

The kinetic theory model relates pressure, volume, and mean kinetic energy of a fixed mass of gas.

What is the significance of elastic collisions in the kinetic theory?

Elastic collisions ensure that kinetic energy is conserved during the collisions between gas molecules.

What does the term 'mean square speed' represent?

Mean square speed represents the average of the squares of the velocities of all gas molecules.

What is the relationship between pressure and the number of molecules in a gas?

The total pressure of the gas is the sum of the individual pressures caused by each molecule.

How does the kinetic theory assume the motion of gas molecules?

The kinetic theory assumes that gas molecules move randomly and in straight lines between collisions.

What is the Boltzmann constant?

The Boltzmann constant (k) relates the average kinetic energy of particles in a gas with the temperature.

How does the volume of a gas relate to the pressure exerted by its molecules?

The pressure exerted by gas molecules is inversely proportional to the volume of the gas.

What happens to the pressure of a gas if its volume increases, assuming constant temperature?

If the volume of a gas increases, its pressure decreases, assuming temperature remains constant.

What is the implication of the assumption that 'no intermolecular forces act on the molecules'?

This assumption simplifies the model by allowing the analysis of gas behavior without considering attractive or repulsive forces between molecules.

What is the importance of the kinetic theory in understanding gas behavior?

The kinetic theory provides a molecular-level explanation for the macroscopic properties of gases, such as pressure and temperature.

What is the equation for the speed of molecules in three dimensions?

c² = u² + v² + w², where u, v, and w are the velocity components in the x, y, and z directions.

What assumption can be made about the mean square speed of particles in three dimensions?

The mean square speed in each direction (u², v², w²) is the same.

What is the relationship between the internal energy and potential energy of an ideal gas?

An ideal gas has no potential energy; its internal energy is equal to the sum of the kinetic energies of all its particles.

What is the equation relating pressure, volume, number of molecules, and absolute temperature of an ideal gas?

p = NkT/V, where k is the Boltzmann constant.

How can the average kinetic energy of a molecule be derived using the ideal gas equation?

By setting the equations for average kinetic energy and the ideal gas equation equal to each other and simplifying.

What is the equation for average kinetic energy of a molecule derived from the kinetic theory?

E_k = (3/2)(kT), where E_k is the average kinetic energy, k is the Boltzmann constant, and T is the absolute temperature.

What defines a black body radiator?

A black body radiator is a perfect emitter and absorber of all possible wavelengths of radiation.

What do radiation curves represent?

Radiation curves are graphs of intensity against wavelength of radiation emitted by objects at different temperatures.

What does Stefan's law state about the power output of a black body radiator?

The power output (luminosity L) is directly proportional to its surface area (A) and the fourth power of its absolute temperature (T): L = σAT⁴.

What is the Stefan constant value?

The Stefan constant (σ) is 5.67 x 10⁻⁸ W m⁻² K⁻⁴.

What does Wien's displacement law state?

Wien's law states that the peak wavelength (λ_max) of emitted radiation is inversely proportional to the absolute temperature (T) of the object.

What is the formula for Wien's displacement law?

λ_max = 2.898 x 10⁻³ mK / T, where mK is meters-Kelvin.

How does the peak wavelength of a black body change with temperature?

The peak wavelength decreases as the temperature increases, indicating that frequency and energy of the wave increase.

What is the significance of the peak wavelength in relation to black body radiation?

The peak wavelength (λ_max) is the wavelength of light released at maximum intensity.

How can Wien's law be used practically?

Wien's law can be used to estimate the temperature of black-body sources.

What is the relationship between temperature and frequency according to Wien's law?

As the temperature of a black body increases, the frequency of emitted radiation increases.

What is the relationship between the kinetic energy of gas molecules and temperature?

The average kinetic energy of gas molecules is directly proportional to the absolute temperature.

What happens to the energy of a wave as its frequency increases?

The energy of the wave increases as the frequency increases.

What is the implication of perfect elastic collisions in an ideal gas?

In an ideal gas, there are no intermolecular forces acting between molecules, leading to perfectly elastic collisions.

What does the term 'internal energy' refer to in the context of an ideal gas?

Internal energy refers to the total kinetic energy of all particles in the gas, as there is no potential energy.

What is the significance of the equation V = NkT/p in thermodynamics?

This equation describes the relationship between the volume, number of molecules, temperature, and pressure of an ideal gas.