Questions I Got Wrong In Papers 2

Question 1

Explain what happens to the proportion of alpha particles that bounce back when they are fired into a thin sheet of gold when: - the thickness of the gold sheet increases - the kinetic energy of the alpha particles increases

Answer 1

• more alpha particles will be reflected as there is a greater chance of an alpha particle coming head on towards a nucleus. - the speed and hence the momentum increases of the alpha particles and therefore they spend less time near the nucleus and so there is less time for the electric field to act on the particle and so less are bounced back.

Question 2

Suggest two modifications to the generator that would increase the emf induced without changing the speed of the rotor.

Answer 2

• stronger magnet - larger number of turns of coil - reduced air gap - core of larger area - laminated core - core of higher permeability

Question 3

What does the area under a graph of electric field strength vs distance show between point x and point 2x?

Answer 3

The potential difference between x and 2x. Work done in moving unit charge between x to 2x.

Question 4

In an attempt to model the discharge of the capacitor, a student uses the equation ΠQ = -Q/RC x ΠT.

The equation allows a series of values of charge Q to be calculated at equal time steps ΠT.

The value of the time step ΠT has been chosen as 20s.

The values of charge calculated above are in poor agreement with the ones obtained from the experiment. Explain the cause of the discrepancy.

Answer 4

model assumes constant charge / current / p.d. in time Πt; in practice charge / current / p.d. decreases with time; so calculated ΠQ too large / calculated Q too small;

Question 5

Explain why the chnage in momentum Πp of the wall when the particle bounces off it is given by Πp = 2mv, towards the right.

Answer 5

Πp = mv - (-mv) (= 2mv);

total momentum of particle and wall doesn’t change;

Question 6

The table shows how the fluidity of ethanol varies with temperature.

Peform a test on the data in the table to show that the fluidity does not increase expontentially with temperature.

Answer 6

EITHER ratio of adjacent values of fluidity constant: 530/920 = 0.58, 920/1500 = 0.61, 1500/2200 = 0.68 OR ratio of adjacent values of fluidity constant: 920/530 = 1.7, 1500/920 = 1.6, 2200/1500 = 1.5 OR difference between adjacent values of ln(fluidity) constant: +(-)0.55, +(-)0.49, +(-)0.38

Question 7

Answer 7

Question 8

Explain how the boltzmann factor accounts for the way that the fluidity of ethanol increases with temperature.

Answer 8

BF/e^-E/kt increases with increasing temperature; BF is probability that a particle can change position / proportion of particles which can move / fraction of particles which can move;