The diameter of the moon is `3.5 xx 10^3 km` and its distance from the earth is `3.8 xx 10^5 km`. It is viewed by a telescope which has `f_o = 4 m` and `f_e = 10 cm`. Find the angle subtended at the eye by the final image.
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Here, `l = 3.5 xx 10^(3) km = 3.5 xx 10^(6)m`, `r = 3.8 xx 10^(5) km = 3.8 xx 10^(8)m` `f_(0) = 4m = 400 cm, f_(e) = 10 cm, beta = ?` `m = (f_(0))/(f_(e)) = (400)/(10) = 40` Also, `m = (beta)/(alpha)` `:. beta = m alpha = 40 xx ((l)/(r )) = 40 xx (3.5 xx 10^(6))/(3.8 xx 10^(8))rad` `= 36.84 xx 10^(-2) xx (180^(@))/(pi) = 21.1^(@)`
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