| Date | May 2015 | Marks available | 2 | Reference code | 15M.3.SL.TZ1.21 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 21 | Adapted from | N/A |
Question
This question is about a converging (convex) lens.
A small object is placed a distance 2.0 cm from a thin convex lens. The focal length of the lens is 5.0 cm.
(i) Deduce the magnification of the lens.
(ii) State and explain the nature of the image formed by this lens with the object at this position.
The object is coloured and the image shows chromatic aberration. Explain what is meant by chromatic aberration.
Describe how the effects of chromatic aberration may be reduced.
Markscheme
(i) attempted substitution into thin lens equation; (allow incorrect signs)
\(v = \left( {\frac{{2 \times 5}}{{2 - 5}}} \right) = \left( - \right)3.3\);
\(m\left( { = - \frac{v}{u}} \right) = \frac{{3.3}}{2} = 1.7\);
(ii) virtual because v is negative;
erect/upright because virtual/because m is positive;
enlarged/magnified because m is greater than 1;
Do not allow correct properties without an explanation.
different colours/wavelengths/frequencies have different refractive indices/speed of light (in glass);
(image with colour distortions due to the) different focal points (of said colours/wavelengths/frequencies);
use of a chromatic doublet / use of a combination of lenses;
