Paper 3 Tips: Practical Test
Do not panic if the context of the practical experiment appears unfamiliar. Where appropriate the question paper will tell you exactly what to do and how to do it.
If you find yourself in real difficulty setting up your practical equipment you may ask your supervisor for help, you will only lose one or more marks for this.
There are a number of things that you can do to save time: Draw a single table for your results in advance of taking any readings and enter your readings in the table as you take them (so that you do not waste time having to copy them up later).
This is also important because you must record all your raw readings before you calculate and record any average readings.
If the number of readings that you need to take is indicated in the question paper do not waste time by exceeding this number. Repeat your readings, but remember that it is only necessary to repeat them once (so that you have two sets of values) - do not waste time repeating them more than once.
All the raw readings(记得是测量数据哦，可不是计算得值哦!) of a particular quantity should be recorded to the same number of decimal places which should in turn be consistent with the uncertainty in the readings.
The uncertainty in a measurement can sometimes be larger than the smallest interval that can be measured by the measuring equipment. For example, a stopwatch can measure time to a hundredth of a second, but human reaction times will mean that the uncertainty in the reading given by a stopwatch is (typically) 0.1s to 0.4s.
Each column heading in your table must contain both a quantity and its unit. For instance if you have measured time “t” in seconds, your column heading would be written as “t/s” (“t in s” or “t(s)” would also be acceptable). The quantity or unit or both may also be written in words rather than symbols. (这就是传说中的表头了，这可是阅卷人评阅表格的第一项，第一印象的重要性就不要我重复了吧。)
The number of significant figures used in a derived quantity that you calculate from your raw readings should be equal in number to (or possibly one more than) the number of significant figures in the raw readings.
For example, if you measure potential difference and current to 2 and 3 sig figs respectively, then the corresponding value of resistance calculated from them should be given to 2 or 3 sig figs, but not 1 or 4. If both were measured to 3 significant figures, then the resistance could be given to 3 (or 4) sig figs. (从这里也可以看出，同一竖向列里的数据，有可能小数点后的位数会不同，但并不影响结果。)
When drawing your graph, do not forget to label each axis with the appropriate quantity and unit,(和表头一样重要，您自己掂量，是不是应该在选取分度值之前先把他们给标上呢?)
using the same format for expressing column headings in a table. Choose a scale such that the plotted points occupy at least half the graph grid in both the x and y directions.(此处有技巧，减减除除约约，完事!)
The x-axis scale should increase positively to the right and the y-axis scale should increase positively upwards. Use a convenient scale such as 1, 2 or 5 units to a 50px square (建议您就用这个吧，别弄个3,4,6的，搬了石头砸自己的脚，好疼的!)
as you will then be less likely to make a mistake with the position of your plotted points and it will be easier for you to read off points from your graph if you are calculating the gradient or finding an intercept. Similarly, it is good practice to mark values on at least every other 50px square.
All your plotted points should be on the grid; points in the white margin area will be ignored. Plot all your observations and ensure that they are accurate to half a small square. A fine cross (or an encircled dot) drawn with a sharp pencil is acceptable, but be careful not to obscure the position of your points by your line of best fit or other working.
When drawing your line of best fit, ensure you have an even balance of points about the line along its whole length. If it is a straight line, use a clear plastic rule so that you can see points on both sides of the line as it is being drawn.
Show all your working when calculating a gradient. It is helpful to draw the triangle(做好虚线的直角三角形哦) used to calculate the gradient on the graph and to clearly label the coordinates of the vertices(标好您所选择的用来计算斜率的两个点的坐标) (accurate to half a small square). These values can then be used in the gradient calculation. The length of the hypotenuse of the triangle should be greater than half the length of the graph line.
If you are required to give a value for the y-intercept, it may be possible to directly read it off from your graph(如果直线与y轴有交点，太好了，直接读取) from an axis where x=0. If this is not possible you can instead calculate the y-intercept by using the equation of a straight line.
In this case you should substitute into this equation a pair of x and y values from your line of best fit along with your calculated value of gradient.