Compare the focal lengths needed for the objective lens in an refracting telescope and in a compound microscope.

A student has four converging lenses of focal length 5, 20, 150 and 500 mm. Determine the maximum magnification that can be obtained with a refracting telescope using two of the lenses.

There are optical telescopes which have diameters about 10 m. There are radio telescopes with single dishes of diameters at least 10 times greater.

(i) Discuss why, for the same number of incident photons per unit area, radio telescopes need to be much larger than optical telescopes.

(ii) Outline how is it possible for radio telescopes to achieve diameters of the order of a thousand kilometres.

The diagram shows a schematic view of a compound microscope with the focal points f_o of the objective lens and the focal points f_e of the eyepiece lens marked on the axis.

On the diagram, identify with an X, a suitable position for the image formed by the objective of the compound microscope.

Image 1 shows details on the petals of a flower under visible light. Image 2 shows the same flower under ultraviolet light. The magnification is the same, but the resolution is higher in Image 2.

Explain why an ultraviolet microscope can increase the resolution of a compound microscope.

\(\frac{{500}}{5}\)
OR
100 times

i
RF photons have smaller energy, so signal requires larger dish

RF waves have greater wavelength, good resolution requires larger dish
Must see both, reason and explanation.

ii
use of an array of dishes/many mutually connected antennas «so the effective diameter equals to the distance between the furthest antennas»

between f_e and eyepiece lens, on its left

Accept any clear indication of the image (eg: X, arrow, dot).
Accept positions which are slightly off axis.