Measure and note the height $H$ of the triangular object.
The student turns on the lamp, positions the lens $u = 20.0\,\text{cm}$ from the object and moves the screen until a sharp image appears.
Measure the image height $h$ on the screen shown in Fig. 3.3.
Calculate the value of $\frac{1}{h}$. Give your answer to 2 significant figures.
Complete the headings by supplying suitable units and work out the remaining values of $\frac{1}{h}$ in Table 3.1.
Suggest why the student does not use $u$ values below $20.0\,\text{cm}$.
On the grid provided, plot $\frac{1}{h}$ on the $y$-axis against $u$ on the $x$-axis. Begin both axes at the origin $(0,0)$ and draw the straight line of best fit.
Calculate the gradient $m$ of your line. Show all working and indicate on the graph the values you use.
Calculate the focal length $f$ of the lens using $f = \frac{1}{mH}$.
Suggest one improvement to the apparatus that would solve the problem of the student’s hand and ruler blocking the light while measuring $h$.