A-level physics paper 1 2025
5 key assumptions of kinetic theory model - correct answer1. molecules are in constant random straight
line motion
2. the volume of a single molecule is negligible in comparison to the distance between molecules
3. collisions are elastic (no KE lost)
4. No intermolecular forces between molecules
5. total energy remains constant
Compare the mean KE of argon atoms and helium atoms in a gas mixture? - correct answerboth have
same mean KE
Derivation of the Kinetic Theory Model Equation (5 steps)While deriving state the assumptions at each
step.Also derive the kinetic energy of a gas molecule from previous derivation. - correct answerconsider
a cube container with length l:
1. find change in momentum for a single molecule hitting a wall perpendicularly.
- assuming molecules rebound elastically (no kinetic energy lost in collision)
- molecule moves at -c and after rebounding moves at +c
- Δp = −mc − (+mc) = −mc − mc = −2mc
2. Find the time between collisions of the molecule on the wall.
- molecule goes from one side of the cube, perpendicularly rebounds at the other side and returns to its
original position
- Δt = 2l/c
3. Find the force exerted on one wall by the molecule.
- Force = Δp/Δt = (2mc)/t = (2mc^2)/2l = (mc^2)/l
- we just ignored the minus sign since technically the force is in the opposite direction by this is just a
stupid way of making the maths easier.
, 4. Calculate total pressure from N molecules on one wall.
- Pressure of one molecule = Force/area = (mc^2)/(l^3)
- For N molecules, each molecule has a different speed so we must find cᵣₘₛ.
- cᵣₘₛ = sqrt.((c1^2 + c2^2 + c3^2 +....+cN^2)/N)
- this is done to change velocities to speeds by squaring to remove direction considerations, find the
mean of the squared speeds and square root them to get the mean speed.
- Pressure of N molecules = (Nmcᵣₘₛ^2)/(l^3) = (Nmcᵣₘₛ^2)/V where V is volume of cube
- rearrange to get pV = Nmcᵣₘₛ^2
5. Consider direction
- the cᵣₘₛ is a speed but can also be considered as the total velocity vector if no velocities were negative.
- therefore we can split up cᵣₘₛ into c_x = c_y = c_z where cᵣₘₛ = c_x + c_y + c_z
- therefore c_x = cᵣₘₛ/3
- therefore pV = 1/3 * Nmcᵣₘₛ^2
(don't really need to understand 3 and 5)
draw particle tree as practice - correct answer
draw the feynman diagram for anineutrino-proton collision - correct answer7
draw the feynman diagram for electron capture - correct answer5
draw the Feynman diagram for electron-proton collision - correct answer8
draw the feynman diagram for neutrino neutron collision - correct answer6
Draw the feynman diagram for the beat minus decay - correct answer3
draw the feynman diagram for the beta plus decay - correct answer4
5 key assumptions of kinetic theory model - correct answer1. molecules are in constant random straight
line motion
2. the volume of a single molecule is negligible in comparison to the distance between molecules
3. collisions are elastic (no KE lost)
4. No intermolecular forces between molecules
5. total energy remains constant
Compare the mean KE of argon atoms and helium atoms in a gas mixture? - correct answerboth have
same mean KE
Derivation of the Kinetic Theory Model Equation (5 steps)While deriving state the assumptions at each
step.Also derive the kinetic energy of a gas molecule from previous derivation. - correct answerconsider
a cube container with length l:
1. find change in momentum for a single molecule hitting a wall perpendicularly.
- assuming molecules rebound elastically (no kinetic energy lost in collision)
- molecule moves at -c and after rebounding moves at +c
- Δp = −mc − (+mc) = −mc − mc = −2mc
2. Find the time between collisions of the molecule on the wall.
- molecule goes from one side of the cube, perpendicularly rebounds at the other side and returns to its
original position
- Δt = 2l/c
3. Find the force exerted on one wall by the molecule.
- Force = Δp/Δt = (2mc)/t = (2mc^2)/2l = (mc^2)/l
- we just ignored the minus sign since technically the force is in the opposite direction by this is just a
stupid way of making the maths easier.
, 4. Calculate total pressure from N molecules on one wall.
- Pressure of one molecule = Force/area = (mc^2)/(l^3)
- For N molecules, each molecule has a different speed so we must find cᵣₘₛ.
- cᵣₘₛ = sqrt.((c1^2 + c2^2 + c3^2 +....+cN^2)/N)
- this is done to change velocities to speeds by squaring to remove direction considerations, find the
mean of the squared speeds and square root them to get the mean speed.
- Pressure of N molecules = (Nmcᵣₘₛ^2)/(l^3) = (Nmcᵣₘₛ^2)/V where V is volume of cube
- rearrange to get pV = Nmcᵣₘₛ^2
5. Consider direction
- the cᵣₘₛ is a speed but can also be considered as the total velocity vector if no velocities were negative.
- therefore we can split up cᵣₘₛ into c_x = c_y = c_z where cᵣₘₛ = c_x + c_y + c_z
- therefore c_x = cᵣₘₛ/3
- therefore pV = 1/3 * Nmcᵣₘₛ^2
(don't really need to understand 3 and 5)
draw particle tree as practice - correct answer
draw the feynman diagram for anineutrino-proton collision - correct answer7
draw the feynman diagram for electron capture - correct answer5
draw the Feynman diagram for electron-proton collision - correct answer8
draw the feynman diagram for neutrino neutron collision - correct answer6
Draw the feynman diagram for the beat minus decay - correct answer3
draw the feynman diagram for the beta plus decay - correct answer4
