Physics Question about magnification.
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Physics Question about magnification.

[From: ] [author: ] [Date: 12-07-16] [Hit: ]
I know that the object distance = do = 30.0cm and the image height= 1.I keep getting the wrong answer- plz help, and it would be nice if you exlpained it also- thanks-As the image is upright and magnified it is virtual (formed behind the mirror) so image distance di is negative.Magnification ........
A person’s face is 30.0 cm in front of a concave makeup mirror, producing an upright image that is 1.45 times as large as the object. What is the mirror’s focal length f?
--answer in cm

Before anyone says do your own homework, I know that the object distance = do = 30.0cm and the
image height= 1.44 times *h0

The magnification equation is:
m = - di/do =hi/ ho

The mirror equation is:
1/d0 + 1/di = 1/f


I keep getting the wrong answer- plz help, and it would be nice if you exlpained it also- thanks

-
As the image is upright and magnified it is virtual (formed behind the mirror) so image distance di is negative.(-di)

Magnification .. m = 1.45 = di/do** .. .. di = 1.45 x 30cm = (-)43.5 cm

Using .. 1/do + 1/-di = 1/f
1/30 - 1/43.5 = 1/f
1/f = 0.01034 .. .. .. ►f = 96.70 cm
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