Question

an object 5 cm in size is placed at 12 cm in front of concave mirror of radius of curvature 20 cm . At what distance from the mirror should or screen be placed in order to obtain a sharp image . find the nature and size of image .​

Answer 1

Given u = 12cm, As mirror is concave so u = -12cm

v = ?

f = R/2 = 20/2 = 10cm, here -> -10cm

\begin{gathered} \frac{1}{u} + \frac{1}{v} = \frac{1}{f} \\ \\ \frac{1}{ - 12} + \frac{1}{v} = \frac{1}{ - 10} \\ \\ \frac{1}{v} = \frac{1}{12} - \frac{1}{10} \\ \\ \frac{1}{v} = \frac{5 - 6}{60} \\ \\ \frac{1}{v} = \frac{ - 1}{60} \\ \\ v = - 60cm\end{gathered}

In order to obtain a sharp image,screen should be placed at a distance of 60cm in front of the mirror.

Size of image ->

where h' is the height of image and h is the height of the object.

Answer 2

$\huge{\boxed{\mathfrak{\overbrace{\underbrace{\fcolorbox{r}{red}{✯Answer}}}}}}$

Given u = 12cm, As mirror is concave so u = -12cm

v = ?

f = R/2 = 20/2 = 10cm, here -> -10cm

$\frac{1}{u} + \frac{1}{v} = \frac{1}{f} \\ \\ \frac{1}{ - 12} + \frac{1}{v} = \frac{1}{ - 10} \\ \\ \frac{1}{v} = \frac{1}{12} - \frac{1}{10} \\ \\ \frac{1}{v} = \frac{5 - 6}{60} \\ \\ \frac{1}{v} = \frac{ - 1}{60} \\ \\ v = - 60cm$

In order to obtain a sharp image,screen should be placed at a distance of 60cm in front of the mirror.

Size of image ->

where h' is the height of image and h is the height of the object.

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