Question

when an object is placed at a distance of 15 cm from a concave mirror its image is formed at 10 cm of the mirror . calculate the focal length of the mirror​

Answer 1

Answer:

above is the answer of your questions

Answer 2

Given :

▪ Distance of object = 15cm

▪ Distance of image = 10cm

▪ Type of mirror : concave

To Find :

▪ Focal length of concave mirror.

Formula :

✳ Mirror formula :

$\orange{\bigstar}\:\underline{\boxed{\bf{\purple{\dfrac{1}{u}+\dfrac{1}{v}=\dfrac{1}{f}}}}}\:\orange{\bigstar}$

• v denotes distance of image
• u denotes distance of object
• f denotes focal length of mirror

Calculation :

$:\implies\sf\:\dfrac{1}{u}+\dfrac{1}{v}=\dfrac{1}{f}\\ \\ :\implies\sf\:\dfrac{1}{(-15)}+\dfrac{1}{(-10)}=\dfrac{1}{f}\\ \\ :\implies\sf\:\dfrac{-2-3}{30}=\dfrac{1}{f}\\ \\ :\implies\sf\:f=\dfrac{-30}{5}\\ \\ :\implies\underline{\boxed{\bf{\red{f=-6cm}}}}\:\orange{\bigstar}$

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✴ Extra Dose :

• X-coordinate of centre of curvature and focus of concave mirror are negative and those for convex mirror are positive.
• In case of mirrors since light rays reflects back in X-direction, therefore -ve sign of v indicates real image and +ve sign of v indicates virtual image.