1. The problem statement, all variables and given/known data I have to find f and d Here's the method of the lab Method: The length of the opening in the ray box was measured and recorded. The equipment was set up as shown in the diagram. The distance, x, of the tube from the screen was varied and recorded. The magnification, m, for each value of x was determined and recorded; this was obtained by focusing the image of the cross-wire formed on the screen and measuring the length of the image using the graph paper attached to the screen. At least 8 values of x and m were determined. A graph of m against x was plot and a best straight line was drawn through the points. Theory suggested that m = (x + d) - 1 f By writing the equation above in the form y=mx + c, the focal length of the lens and the position of the lens from end A of the cardboard tube was determined. 2. Relevant equations m = (x + d) - 1 f 3. The attempt at a solution I plotted a graph of m against x gradient = m/x so gradient would = 1/f right? then i could solve for d after?