Question

an object is placed 20cm infront of a convex mirror and the image is formed 10cm from the mirror. calculate the new image if object is moved 5cm towards the mirror.​

Answer 1

law of conservation. Conservation law, also called law of conservation, in physics, several principles that state that certain physical properties (i.e., measurable quantities) do not change in the course of time within an isolated physical system.

Answer 2

• Distance of object from mirror = 20cm

• Distance of image from mirror = 10cm

Let focal length of mirror be f.

According to the question :-

$\rm \longrightarrow\dfrac{1}{10} + \dfrac{1}{( - 20)} = \dfrac{1}{f} \\ \\ \\ \rm \longrightarrow\dfrac{1}{10} - \dfrac{1}{20} = \dfrac{1}{f} \\ \\ \\ \rm \longrightarrow \dfrac{2 - 1}{20} = \dfrac{1}{f} \\ \\ \\ \rm \longrightarrow \dfrac{ 1}{20} = \dfrac{1}{f} \\ \\ \\ \\ \\ \rm \longrightarrow \: 20 \: cm = f$

Therefore, focal length of mirror = 20 cm

Now, if object is moved 5cm towards the mirror then distance of object from mirror = 20cm - 5 cm

= 15 cm

Let new image distance be v.

According to the question :-

$\rm \longrightarrow \dfrac{1}{v} + \dfrac{1}{( - 15)} = \dfrac{1}{20} \\ \\ \\ \rm \longrightarrow \dfrac{1}{v} = \dfrac{1}{20} + \dfrac{1}{ 15}\\ \\ \\ \rm \longrightarrow \dfrac{1}{v} =\dfrac{3 + 4}{60}\\ \\ \\ \rm \longrightarrow \dfrac{1}{v} =\dfrac{7}{60}\\ \\ \\ \rm \longrightarrow {v} =\dfrac{60}{7}cm$

Therefore , new image distance = 60/7 = 8.57 cm