A student investigates how the resistance of a wire depends on its length.
The photograph shows the circuit that the student uses.
(a) Draw a circuit diagram to show how the components in the photograph are connected.（3）
(b) (i) Complete the table by naming the key variables in this investigation.（1）
(ii) Describe the method the student should use for this investigation.（5）
参考答案及解题思路
Part A is relatively straightforward; it requires the student to see the above photograph and to reproduce it in the style of a circuit diagram, which they should be very familiar with drawing (voltmeter in parallel, ammeter in series).
Part A比较简单; 学生只需要将图片上的内容以电路图的方式画出来即可，考生需要非常熟悉绘图（电压表并联，电流表串联）。
The second part is more interesting; it expects the student to produce an experimental design and, generously, provides some organisation in first identifying the variables.
第二部分就显得有趣多了，题目要求学生根据第一部分提供的变量做一个实验设计。
The independent variable is the one that you, the scientist, control and vary as you conduct the experiment. In this case the length of the wire.
The dependent variable is the one that depends upon the independent variable; we measure this one to determine how it changes as we change the independent variable.In this case, the resistance - determined by measurements of current and voltage.
For five marks you must then describe the experiment:
题目共5分，所以必须要描述这个实验。
The first point is to set up the apparatus as shown in the diagram.
Having determined the variables earlier in the question, the second step is to write down how you will measure these. The independent variable will be controlled by adjusting the position of the crocodile clip on the wire (see photograph) and will be measured with the ruler. The dependent variable will be measured by taking readings from the voltmeter and ammeter at a given length of wire and using the equation V = IR to determine resistance. Further readings are then taken at different lengths of wire.The next point is to mention repeat measurements, taking an average.
Experimental accuracy should be considered. Following the scientific method, other factors that may affect the result must be controlled. In this instance temperature would have a significant effect. The wires should, therefore, be disconnected between readings to avoid them heating up, which would change the readings. The voltmeter and ammeter should also be checked for zero errors (there should be 0 current when no power supplied).
Five marks could be achieved by mentioning fewer points than listed here.
In summary:
总结：
1.确定变量
2. 描述实验设置以及变量的测量
3. 考虑实验准确性，控制变量以及如何控制