Physics AS P3

Okay you people, Sir Puran has been kind to say most of there is to know about Paper 3, so this part of the exam shouldn't bee too much to worry about. I'll list some points to remember when doing this paper.

I ran out of time, so I wouldn't say that this would be a complete work, but I hope it'll still be helpful.

I've covered all aspects of graph-making (I hope), and some of measurements. However, I'm unable to post a say on the others, so I really encourage you to read this particular handout:

PHYSICS A/AS
9702

DEFINITIONS AND FORMULAE

That's the title of the handout, but that part is none of our concern; what's important in that paper is the next part; it has all the information minus graph drawing. (Nearly a bible, but hey, I did graphs already; scroll down)

If you're not reading it, then it's your own problem if you lose marks because some idiot asks you to plot the graph logarithm style, or if you mess up your significant figures.

Measurements

• Read and follow the instructions carefully to the letter.
• Wherever your common sense tells you to, take repeated readings. (Usually around 4 to 6 times) Also, make sure these repeated readings are not uselessly repeated. (e.g. Measuring the diameter of the wire at the same location and without rotating it. Go figure why)
• Be aware of the Power of Tens.
• And check your formulae.
• Do make sure that you have utilised most of the given range in taking your measurements. (i.e. If given a range between 0 to 1 metre, at least use 0.1 to 0.9 metres)
• The difference between each measurement should be roughly equal. (i.e. Take, for example, 0.2, 0.4, 0.6, 0.8, and so on)

Graphs

Since I lack the software needed to draw graphs + I'm too lazy to make one on mspaint.exe, there will be no illustrations here.

Also, since it has been ages since CIE released a paper where candidates are required to plot a curve, I suggest you bring your flexible ruler.

Anyway,

For graphs, here are the 5 points to remember:

• Choice of scale
• Plotting of points
• Line of best fit
• Calculation of gradient
• Determination/calculation of the y-intercept

Choice of scale

• You must make sure that the scale you choose will make your graph occupy more than half of the graph paper.
• Label the axes. (Include the quantity in question and its unit)
• Make sure that your scale is conventional! (As in: Don't make it so that people will have to read it right to left, like Arabian script; etc.) Remember this when plotting negative numbers, ja?
• No fancy scales. That means on the big squares, don't try using 3, 6, 9, 12, etc. or anything that 1) Makes it hard for you to read, and 2) Makes it hard for you to plot.
• It is recommended to not leave space for labeling each big square. (i.e. Do: 0, 5, 10, 15; not 0, nothing, nothing, 15)
• Scaling must also be regular. (e.g. 5, 10, 15; not 5, 11, 20)

Plotting of points

• Don't plot outside the given area/margin. (Outside the big, boxy thingies)
• All data must be plotted. (e.g. If you have made 7 observations, the examiner must see 7 plots in the graph)
• If you must plot let's say, 0.43 m, and your smallest box represents 0.2 m, you will have to approximate this plot. The room for error given by the examiner is half of this value. (In this case, ± 0.1)
• The plot must be clear enough for the examiner to see.
• Don't make your plots very thick, as they examiner may not be able to see accurately whether you have plotted the corresponding observation correctly in the graph, resulting in the loss of marks. It is also due to this that you use crosses to mark plots and not dots.

Line of best fit

• There must be at least 5 plots for the 'best fit' mark to be awarded. (No problem, really, given that the question usually requests for 6)
• The line of best fit must be 'balanced', at least roughly. Simply put, if you have 3 plots above the line of best fit, then have 3 plots below the line of best fit too.
• Lines must thin and clear. This is not an art examination, so avoid unnecessary ornaments like making thick lines and having jembut branch from it et cetera et cetera. Curves are usually prone to this. (Let's hope you didn't throw away your flexible ruler)
• Lines must extend reasonably further than the last greatest plot, reach x = 0, but not extend to less than x = 0. (At least so far, don't ask me if this still applies if we have to plot both negative and positive values)

Calculation of gradient

• Make a right triangle to indicate from where are you taking the coordinates to include in your calculation.
• Take the coordinates which lie on the line of best fit, not from the plot which is used to make the line of best fit.
• Indicate those coordinates in the graph. (e.g. If you take one value to be (1.24, 3.22), then write (1.24, 3.22) on (1.24, 3.22) on the graph)
• The triangle must cover more than ⅔ of the whole curve.
• ∆y and ∆x must be accurate to the smallest square in your graph.
• I cannot say if we would need units for the gradient, since my own experience and various sources conflict. Therefore, use your own judgment, or go ask somebody credible.
  
• Workings workings workings! Show them!

Determination/calculation of the y-intercept

• y-intercept is always read from x = 0, x = 0, x = 0.
• If you cannot read the y-intercept of the graph, then you have to calculate it using the equation y = mx + c. To do this, take any value from the line of best fit and substitute those values into the equation. (I'm not sure, but to be on the safe side, do indicate these values on the graph, like you would with a gradient-calculation coordinate)
• The y-intercept has units. (Usually)