An IGCSE physics class is carrying out an experiment to determine the focal length of a converging lens.
A student measures the object distance u u\,u and image distance v v\,v from a diagram drawn to 14\displaystyle \frac{1}{4}41th full size.
On this diagram, the measured distances are:
(i) Determine the actual values, in metres, of u u\,u and v v\,v for this measurement.
(ii) Calculate the corresponding values of 1u\displaystyle \frac{1}{u}u1 and 1v\displaystyle \frac{1}{v}v1 in m−1\text{m}^{-1}m−1.
Four more object distances are set up and these and the corresponding image distances are recorded in Table 4.1.
Table 4.1
| u / mu\ /\ \text{m}u / m | 1u / m−1\displaystyle \frac{1}{u}\ /\ \text{m}^{-1}u1 / m−1 | v / mv\ /\ \text{m}v / m | 1v / m−1\displaystyle \frac{1}{v}\ /\ \text{m}^{-1}v1 / m−1 |
|---|---|---|---|
| 0.200 | 5.00 | 0.400 | |
| 0.250 | 4.00 | 0.286 | |
| [Row 3] | |||
| 0.500 | 2.00 | 0.182 | |
| 0.800 | 1.25 | 0.160 |
Complete Table 4.1 by entering the values from part (a) in Row 3 and calculating the values of 1v\displaystyle \frac{1}{v}v1 for the other rows.
A graph of 1v\displaystyle \frac{1}{v}v1 (yyy-axis) against 1u\displaystyle \frac{1}{u}u1 (xxx-axis) is plotted. Both axes begin at the origin (0,0)(0, 0)(0,0).
(i) From the graph, determine the value p p\,p of 1u\displaystyle \frac{1}{u}u1 when 1v\displaystyle \frac{1}{v}v1 is zero (the xxx-intercept).
(ii) From the graph, determine the value q q\,q of 1v\displaystyle \frac{1}{v}v1 when 1u\displaystyle \frac{1}{u}u1 is zero (the yyy-intercept).
(i) Calculate zzz, where z z\,z is the average value of p p\,p and qqq.
(ii) Calculate the focal length f f\,f of the lens where f=1z\displaystyle f = \frac{1}{z}f=z1.
216 exam-style questions on CIE IGCSE Physics 3.2 Light, covering 3.2.1a Reflection of light, 3.2.1b Images in a plane mirror, 3.2.2 Refraction of light, 3.2.2a Refraction of light, 3.2.2b Total internal reflection, 3.2.2c Refractive index and critical angle, 3.2.2d Optical fibres, 3.2.3a Converging and diverging lenses, 3.2.3b Ray diagrams and the nature of images, 3.2.3c Virtual images and the magnifying glass, 3.2.3d Correcting long-sightedness and short-sightedness, and 3.2.4 Dispersion of light. Each one has a worked solution and a mark scheme showing where the marks go.