Waves

Question 1

It says to comment between two sets of data for Planck consant for waves , how to do in terms of accuracy and precision

Answer 1

The most accurate one is the one closer to real answer
Most precise one is the one with least uncertainty
- explain why = state the uncertainties , and the SHAPE OF THE GRAPH

Question 2

does the shape of the graph being MORE SPREAD OUT determine if it’s less accurate or less precise?

Answer 2

Less PRECISE

Remember we said precise refers to uncertainties

How do we calculate the uncertainty for the value? It’s by drawing the line of WORST FIT, thus if the worst fit line is gonna be more spread, then the uncertainty will be greater and thus less precise

And the uncertainty line is only more spread when the data points are too!

Question 3

Why when we are trying to reduce uncertainty of the double slit experiment can we not say reduce a , keep d thr same, it means x increases so now you can measure more maxima and reduce uncertainty etc?

Answer 3

Because typically you CANT reduce A, it’s fixed, so have to think of other way.

Question 4

So what can you do in your control to reduce uncertainty in all 3 measurements in ax / d experiment?

Answer 4

1) As CANT change the length of a, we have to use some more HIGHER RESOLUTION EQUIPMEMT, such as a slide projector to enlarge the display and use something else?

2) we CAN change distance d, so maximise this (as higher final d means less uncertainty). Also use better equipment (a 2meter ruler stick for example as 2 individual meter sticks are more uncertain)

3) for x , MEASURE THE MOST NUMBER OF MAXIMA YOU CAN , as this massively reduces uncertainty (then divide by total)
- use micrometer or milimeter scale and magnifying glsdd

Question 5

Again what to do to reduce uncertainty for a?

Answer 5

As we can’t change length, must increase resolution

• use a slide projector to display enlarged image of slits on screen and use a more high resolution scale?

Question 6

Why when a photon is transferring energy to a metal, nkt all of the energy may be transferred to a specific area / even reach the metal at all (assuming not reached work function)

IMPORTSNT

Answer 6

• bevause energy can be conducted to the rest of the material
• SCATTERING OF PHOTONS MAY OCCUR ( not specific to x rays)!

Question 7

What does the yr 13 cathode PAG experiment about

Why does the current gradually go down?

Answer 7

Basically an experiment to determine the KE MAX of photons
1) photons induced on a cathode , by photoelectric effect this emits electrons but of A RANGE OF KE, from 0 to ke Max

2) the photons then travel towards the anode, but as there is AN EXTERNAL CIRCUIT with voltage applied producing an electric field, the electrons are REPELLED / HAVE TO DO WORK AGAINST THR FIELD TO REACH THE ANODE
- if it reaches anode, it can contribute current in the circuit

3) the electrons will only be able to scale the length of the distance if their ke > than EV
- as V increases, the lower ke electrons won’t make it and so current falls
- as v increased to match max ke, none of the electrons can make it and so current falls to 0!

Question 8

What does intensity in photoelectric effect link to ?

Answer 8

Not the amount of photons emitted but the RATE of emissions

Thus even if the rate of emission is high, as interactions between photos and electrons happen in 1:1, if the photons don’t have the minimum energy to match the work function, then even if the rwte was high electrons won’t be emitted.

In the particle model of waves, thr energy is ONLH dependent on the frequency of the photons , not the intensity