Question

How far should an object be from a concave mirror of radius 30cm to form a real image 1/6 of its size?
85 cm
95 cm
105 cm
115 cm

Answer 1

Answer on question #52720, Physics, Optics

Question How far should an object be from a concave mirror of radius 30cm to form a real image 1/6 of its size?

85 cm

95 cm

105 cm

115 cm

Solution Focal length of the mirror is $f=R/2=15$ cm. The magnification is

$M=\frac{h_{i}}{h_{o}}=\frac{d_{i}}{d_{o}}=\frac{1}{6}$

so we know that $d_{i}=d_{o}/6$ now we can use mirror equation to find $d_{o}$ -distance of object.

$\frac{1}{f}=\frac{1}{d_{o}}+\frac{6}{d_{o}}=\frac{7}{d_{o}}$

$d_{o}=7f=7\cdot 15=105\,cm$

Answer is 115 cm.