For the concave-mirror case where $u=-25\,\text{cm}$, $f=-15\,\text{cm}$, and $h_1=+4\,\text{cm}$, what is the image height $h_2$?
A$+6\,\text{cm}$
B$-6\,\text{cm}$
C$+4\,\text{cm}$
D$-4\,\text{cm}$
Answer & Solution
Correct answer: B. $-6\,\text{cm}$
First, the image distance is $v=-37.5\,\text{cm}$. Then $m=-\frac{v}{u}=-\frac{-37.5}{-25}=-1.5$, so $h_2=m h_1=-1.5\times 4=-6\,\text{cm}$. The negative sign shows the image is inverted.
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