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Hot goIITian

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13 Apr 2008 07:57:03 IST

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339

Where should the object be placed?

None

Que. - When a object is placed at a distance of 60 cm. from a convex mirror, the magnification produced is 0.5. Where should the object be placed to get a magnification of 1/3?

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Blazing goIITian

Joined: 1 Apr 2007

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13 Apr 2008 09:50:16 IST

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from first condition ..ques. tells u abt v..& hence f..

now u have f &v...calculate for u from magnification formula and mirror formula..

Karan Singh

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13 Apr 2008 11:08:48 IST

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from the first case,
applying magnification and mirror formula, we get f = +60cm.

the we use again magnification and mirror formula taking u = -3v,
we get u = -120 cm which is req answer.

Payal Bonnerjee

Scorching goIITian

Joined: 12 Nov 2007

Posts: 211

14 Apr 2008 00:52:28 IST

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u= -60 cm

m= 0.5

m= -v/u

v= -mu

= -0.5*(-60)

= 30 cm

According to mirror formula,

1/f=1/v+1/u

=1/30+(-1/60)

= 60 cm

New m=1/3

m= -v/u

1/3= -v/u

u=-3v

Again, 1/f=1/v+1/u

1/60= 1/v+(-1/3v)

v= 40 cm

Thus u= - (3*40)

= -120 cm

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