Question 1:
A pupil is supplied with an eyepiece lens which has focal length, fe = 7 cm and four pieces of objective lenses A, B, C and D as shown in Table 6.11.
1. Complete Table 6.11.
2. State two lenses which can produce the largest image.
3. State two lenses which can produce the brightest image.
4. Based on your answers in 2 and 3, state the most suitable lens to be used as the objective lens of a telescope. Explain your answer.
Answer:
(1)
$$ \begin{aligned} &\text { Magnification of telescope at normal adjustment, } M \text { is }\\ &M=\frac{f_{\mathrm{o}}}{f_{\mathrm{e}}} \end{aligned} $$
A pupil is supplied with an eyepiece lens which has focal length, fe = 7 cm and four pieces of objective lenses A, B, C and D as shown in Table 6.11.
1. Complete Table 6.11.
2. State two lenses which can produce the largest image.
3. State two lenses which can produce the brightest image.
4. Based on your answers in 2 and 3, state the most suitable lens to be used as the objective lens of a telescope. Explain your answer.
Answer:
(1)
$$ \begin{aligned} &\text { Magnification of telescope at normal adjustment, } M \text { is }\\ &M=\frac{f_{\mathrm{o}}}{f_{\mathrm{e}}} \end{aligned} $$
Given fe = 7 cm
(2) The two lenses which can produce the largest image are lens C and lens D because they have largest focal length of objective lens.
(3) The two lenses which can produce the brightest image are lens B and lens D because lenses with bigger diameter of objective lens will allow more lights to pass through it.
(4) The most suitable lens to be used as the objective lens of a telescope is lens D because it’s objective lens has longest focal length and biggest diameter.