An object is placed at a distance of 15 cm from a concave lens of focal length 30 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
CBSE OUTSIDE DELHI - SET 3 2017
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Given, u = -15cm (It is to the left of the lens) f = -30 cm (It is a concave lens) Using the lens formula $\frac{1}{\text{f}}=\frac{1}{\text{v}}-\frac{1}{\text{u}}$$\Rightarrow \frac{1}{\text{v}}=\frac{1}{\text{f}}+\frac{1}{\text{u}} =\frac{1}{(-30)} + \frac{1}{(-15)}$
$\therefore \frac{1}{\text{v}}=-\frac{3}{30}=-\frac{1}{10}$
$\therefore \text{v}=-10\text{cm}$
The negative sign of the image distance shows that the image is fromed on the left side of the concave mirror. Thus, the image formed by a mirror is virtual, erect and on the same side as the object.
$\therefore \frac{1}{\text{v}}=-\frac{3}{30}=-\frac{1}{10}$
$\therefore \text{v}=-10\text{cm}$
The negative sign of the image distance shows that the image is fromed on the left side of the concave mirror. Thus, the image formed by a mirror is virtual, erect and on the same side as the object.
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