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The focal lengths of the objective and eyepiece of a microscope are 1.25 cm and 5 cm respectively.

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Question

The focal lengths of the objective and eyepiece of a microscope are 1.25 cm and 5 cm respectively. Find the position of the object relative to the objective in order to obtain an angular magnification of 30 in normal adjustment.

Sum
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Solution

`m_e = D/f_e = 25/5 = 5`

m = m0 × me

`m_0 = m/m_e = -30/5 = -6`

`m_0 = v_0/u_o, -6 = v_0/u_o`

v0 = −6ue

`1/f_e = 1/v_0 - 1/u_0`

`= 1/1.25 = 1/(-6u_0) - 1/u_0 = (-1-6)/(6u_0) = -7/(6u_0)`

`= u_0 = (-7xx1.25)/6`

= −1.46 cm

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2011-2012 (March) Delhi Set 1

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