A spherical mirror produces an image of magnification -1 on a screen placed at a distance of 50cm from the mirror.
- Write the type of mirror.
- find the distance of the image from the object.
- What is the focal length of the mirror?
- Draw the ray diagram to show the image formation in this case.
CBSE DELHI - SET 1 2014
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If magnification, m = -1 v = 50cm If the magnification has minus sign, then the image is real and inverted.$\therefore v = - 50$
$\therefore m = \frac{-v}{u}$
$\Rightarrow - =1 = \frac{(-50)}{-u}$$\therefore u = -50 \text{ cm}$
$\frac{1}{f} = -\frac{1}{50} - \frac{1}{50}$
$\Rightarrow \frac{-2}{50} = \frac{-1}{25}$
$\therefore f = \text{-25 cm}$
$\therefore m = \frac{-v}{u}$
$\Rightarrow - =1 = \frac{(-50)}{-u}$$\therefore u = -50 \text{ cm}$
- Since image is formed on the screen therefore the mirror formed real image which is formed by concave mirror only.
- Image distance = 50cm in front of the mirror.
- $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
$\frac{1}{f} = -\frac{1}{50} - \frac{1}{50}$
$\Rightarrow \frac{-2}{50} = \frac{-1}{25}$
$\therefore f = \text{-25 cm}$
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