# Before of the lens can be solved. Changing

Before starting, drawing around the prism

ensures that the prism can be readjusted if knocked or moved. An additional

insurance can be made by performing this experiment in a dark room, as then the

light is more visible and therefore less mistakes are to be made when following

the lights pathway.

A

white light directed through the one of the two shorter edges of the triangular

block. The light then came out of the block’s hypotenuse. The pathway should be

marked just before the light entered and just after the light exited the block.

After this is done, the block can then be removed and in the white space where

the block once laid, the entry and exit points can be joined. The point where

the block leaves the hypotenuse, a perpendicular line should be draw. Then, two

opposite angles should be taken between the normal and the pathway of light (as

demonstrated in diagram 3)

The two angles can then see

substituted into Snell’s law (see equation 1). Rearranging the equation allows

the unknown medium’s refractive index to be solved, as we know the refractive

index of air is 1.00. This methodology can be repeated several times to gain a

greater amount of precision, and can then be repeated for the other medium.

Diagram 3: how

to label the angles in respect to the normal

Part B: parallax method:

A bench with two pins on either side of a

convex lens should be set up. Using this set up, the focal length of the lens

can be solved. Changing the object pin, the independent variable, should be

changed several times to different lengths of ‘u’ – distance between the pin

and the lens. By changing this, we can then change the dependent variable, the

‘image-finder’ pin. As shown in diagram 2, the ‘image finder’ should be

adjusted so at eye-level the two pins just meet. Due to error associated with

this point being visually decided, a second opinion should be taken to whether

they are just touching. The distance between the ‘image-finder’ pin and the

lens can be labelled as ‘v’. This can then be repeated, so there are several

pairs of u and v values. As discussed in the theory, using equation 4, a graph

can be plotted to find the focal length. Comparing this to the general equation

of a straight line, , the gradient of the line of best fit can be allocated to the

focal length.