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Units and Measurements physics ncert solutions class 11th Physics Class 11th Physics NCERT Exemplar Solutions Class 11th Chapter Two

(a) The earth-moon distance is about 60 earth radius. What will be the diameter of the earth (approximately in degrees) as seen from the moon?

(b) Moon is seen to be of (½)° diameter from the earth. What must be the relative size compared to the earth?

(c) From parallax measurement, the sun is found to be at a distance of about 400 times the earth-moon distance. Estimate the ratio of sun-earth diameters.

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Payal Gupta | Contributor-Level 10

4 months ago

This is a short answer type question as classified in NCERT Exemplar

(a)

l=R_E; r= 60R_E

$θ = \frac{R_{E}}{60 R_{E}} = \frac{1}{60} r a d = \frac{1}{60} \times \frac{180}{π} d e g r e e = \frac{3}{π} \approx 1^{o}$

Hence angle subtend is $2^{o}$

(b) But in 2^nd case it is given that moon is (½)° and earth is 2^o so it become 4 times.

$\frac{d i a m e t e r o f e a r t h}{d i a m e t e r o f m o o n} = \frac{2 / π}{1 / 2 π} = 4$

(c) To measure parallax sun is about 400 times the earth moon distance hence $\frac{r_{s u n}}{r_{m o o n}} = 400$

To finding ratio of

$\frac{D_{s u n}}{r_{s u n}} = \frac{D_{s u n}}{r_{m o o n}}$

$\frac{D_{s u n}}{D_{m o o n}} = 400$

$\frac{D_{e a r t h}}{D_{m o o n}} = 4$

so $\frac{D_{s u n}}{D_{e a r t h}} = 100$

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