In Fig. 3.2, take the metre rule readings level with the top of the spring and level with the bottom of the spring. Leave out the top and bottom loops of the spring from your measurements. Write your readings to the nearest $0.1\,\text{cm}$.
Draw on Fig. 3.2 to show the student using a set-square to read the metre rule level with the bottom of the spring.
Calculate the length $l$ of the coiled section of the spring from the equation $l =$ reading level with bottom of spring $-$ reading level with top of spring. Show your method. Enter $l$ in Table 3.1 for a load of $L = 0.0\,\text{N}$.
A load of $L = 1.0\,\text{N}$ is added to the spring. The top of the spring remains stationary, but the bottom of the spring drops. The new metre rule reading level with the bottom of the spring is $45.2\,\text{cm}$. Calculate the new length $l$ of the spring. Record your answer in Table 3.1 for $L = 1.0\,\text{N}$.
On the grid in Fig. 3.3, draw a graph of $l$ on the $y$-axis against $L$ on the $x$-axis. Begin at the origin $(0,0)$. Draw the straight line of best fit.
Use the information in Table 3.1 together with the graph in Fig. 3.3 to find the extension of the spring when a load of $3.5\,\text{N}$ is applied. Show your working. Extension = [BLANK] cm.
A student claims that the stretched length $l$ of the spring is proportional to load $L$. State whether the evidence in Table 3.1 supports this claim. Justify your statement using the data in Table 3.1 or the graph in Fig. 3.3.
Parallax errors may happen when readings are taken from the metre rule. State one practical method, other than using a set square, that makes metre rule readings accurate.
The student carries out the procedure in (c) twice more and then averages the readings before finding the spring lengths $l$ for each load $L$. Explain why the student does this.