Date | November 2020 | Marks available | 2 | Reference code | 20N.3.SL.TZ0.11 |
Level | Standard level | Paper | Paper 3 | Time zone | 0 - no time zone |
Command term | Calculate | Question number | 11 | Adapted from | N/A |
Question
A beam of monochromatic light from infinity is incident on a converging lens A. The diagram shows three wavefronts of the light and the focal point ff of the lens.
Draw on the diagram the three wavefronts after they have passed through the lens.
Lens A has a focal length of 4.00 cm4.00cm. An object is placed 4.50 cm4.50cm to the left of A. Show by calculation that a screen should be placed about 0.4 m0.4m from A to display a focused image.
The screen is removed and the image is used as the object for a second diverging lens B, to form a final image. Lens B has a focal length of 2.00 cm2.00cm and the final real image is 8.00 cm8.00cm from the lens. Calculate the distance between lens A and lens B.
Calculate the total magnification of the object by the lens combination.
Markscheme
wavefront separation identical and equal to separation before the lens ✓
wavefronts converging, approximately centered on ff ✓
By eye.
Dotted construction lines are not required, allow wavefronts to extend beyond or be inside the dotted lines here.
Allow [1 max] if only two wavefronts drawn.
1v=14.00-14.501v=14.00−14.50 ✓
v=36.0 «cm» ✓
A: 1-2.0=18+1u ✓
u=-1.6 «cm» ✓
distance necessary = «36.0-1.6=»34.4 «cm» ✓
Allow [2 max] for ECF for no negative in MP1. Gives u=2.7 and distance of 38.7«cm»
Allow ECF from (b) in MP3.EG use of 0.4 m/40 cm.
«m=-io=-364.5 for A or -8-1.6 for B»
mA=«–»8 OR mB=«+»5 ✓
total magnification =«–» 40 ✓
Allow [2] marks for a bald correct answer
Allow ECF from (b) and (c).
Eg if u=2.7 cm in (c) then mB=3 and total m=24