Chapter 09 Light – Reflection and Refraction Questions-02
Questions
1. Find the focal length of a convex mirror whose radius of curvature is $32 cm$.
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Answer
Radius of curvature, $R=32 cm$
Radius of curvature $=2 \times$ Focal length $(f)$
$R=2 f$
$f=\dfrac{R}{2}=\dfrac{32}{2}=16 cm$
Hence, the focal length of the given convex mirror is $16 cm$.
2. A concave mirror produces three times magnified (enlarged) real image of an object placed at $10 cm$ in front of it. Where is the image located?
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Answer
Magnification produced by a spherical mirror is given by the relation,
$m=\dfrac{\text{ Height of the image }}{\text{ Height of the object }}=-\dfrac{\text{ Image distance }}{\text{ Object distance }}$
$m=\dfrac{h_1}{h_0}=-\dfrac{v}{u}$
Let the height of the object, ho $=h$
Then, height of the image, $hI=-3 h$ (Image formed is real)
$ \begin{aligned} & \dfrac{-3 h}{h}=\dfrac{-v}{u} \\ & \dfrac{v}{u}=3 \end{aligned} $
Object distance, $u=-10 cm$
$v=3 \times(-10)=-30 cm$
Here, the negative sign indicates that an inverted image is formed at a distance of 30 $cm$ in front of the given concave mirror.
