Thermal Physics Flashcards
State two conditions necessary for Boyle’s law
- Constant temperature
- Fixed mass / Fixed number of molecules
Explain why the driver would be less seriously injured in a collision if the air bag inflates than he would be if unrestrained
moving driver has momentum (1)
in sudden impact momentum must be lost in v. short time (1) (you keep missing this point!)
F = Δ(mv) / Δt (or F = ma) (1)
air bag increases stopping contact time (1)
hence reduces force (or reduces force by decreasing the deceleration) (1)
(b) Why is the driver of a car fitted only with seat belts more likely to be injured than if an air bag was fitted? Ignore the different deceleration times and the difference in the materials used.
Seat belt applies force to smaller area than air bag (1)
causing greater pressure on parts of body
Define the Avogadro constant.
the number of atoms in 12g of carbon-12
or
the number of particles / atoms / molecules in one mole of substance ✓
define ideal gas
Explain, in terms of the kinetic theory model, why the pressure drops when the carbon dioxide is released into the life jacket.
volume increase (1)
time between collisions increases (1) speed constant as temp constant (1)
rate of change of momentum decreases (1
Explain why the kinetic theory model would apply more accurately to the gas in the inflated life jacket compared with the gas in the small cylinder.
volume smaller in cylinder (1)
molecules occupy significantly greater proportion of the volume (1) molecules closer so intermolecular forces greater
(a) State two quantities which increase when the temperature of a given mass of gas is increased at constant volume.
pressure (1)
(average) kinetic energy [or rms speed] (1)
Smoke particles are observed to move in a random way. State two conclusions about air molecules and their motion resulting from this observation.
motion of air molecules.
(“they are“)
random (in all directions)
fast moving
air molecules small or much smaller than smoke particles
Why is internal energy = KE in ideal gas
molecules have no potential energy (1)
no attractive forces [or elastic collisions occur] (1)
Use the kinetic theory of gases to explain why
(i) the pressure exerted by an ideal gas increases when it is heated at constant volume.
more collisions (with wall) per second (1)
and more momentum change per collision (1)
greater force because more momentum change per second (greater pressure) (1)
Use the kinetic theory of gases to explain why
The volume occupied by an ideal gas increases when it is heated at constant pressure
same pressure) faster molecules so more momentum change per collision (1) greater volume, fewer collisions per second [or greater volume
to maintain same pressure] (1)
how do you calculate absolute value using a graph (WITH A NEGATIVE SLOPE)
-c/m
c (intercept)
M (gradient)
Suggest why the specific latent heat of vaporisation of water is much greater than the
specific latent heat of fusion of water.
idea that more energy has to be supplied to separate
molecules than to break solid bond
what is internal energy
