Question

For the given object $AB$ of height $4\text{cm}$ and concave mirror of focal length $20\text{cm}$. Here, $h_o$ is the height of the object and $R$ is the radius of curvature.
Select the correct option. ( Use sign convention)

• A. $h_o=+4\text{cm},R=+40\text{cm}$
• B. $h_o=+4\text{cm},R=-40\text{cm}$
• C. $h_o=-4\text{cm},R=+40\text{cm}$
• D. $h_o=-4\text{cm},R=-40\text{cm}$

Answer 1

The correct option is D $h_o=-4\text{cm},R=-40\text{cm}$

As per sign convention,
$\left(1\right)$ All distances are measured from the pole.
$\left(2\right)$ Distance in the direction of the incident ray is taken as positive and in the opposite is taken as negative.
$\left(3\right)$ Distance above the principal axis is taken as positive and below the principal axis as negative.
Based on these rules,
Height of object is $h_o=-4\text{cm}$
Radius of curvature of mirror is $R=2f=-40\text{cm}$