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  • Help me answer: An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be

An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be

  • Option 1)

    30 cm towards the mirror

  • Option 2)

    36 cm away from the mirror

  • Option 3)

    30 cm away from the mirror

  • Option 4)

     36 cm towards the mirror

 

Answers (1)

best_answer

As we have learned

Mirror Formula -

frac{1}{v}+frac{1}{u}=frac{1}{f}


 

- wherein

u= Object distance from pole of mirror.

v= Image distance from pole of mirror.

f= focal length of the mirror.

 

u_{1}= -40cm

f= -15cm

\frac{1}{v_{1}}=\frac{1}{f_{1}}-\frac{1}{u_{1}}=\frac{-1}{15}+\frac{1}{40}=\frac{-8+3}{120}=\frac{-5}{120}

{v_{1}= -24cm

2nd case 

{v_{2}}= -20cm

\frac{1}{v_{2}}=\frac{1}{f}-\frac{1}{u_{2}}=\frac{-1}{15}+\frac{1}{20}=\frac{-4+3}{60}

v_{2}=-60cm

Image gets displaced by 36 cm , away from the mirror  

 

 

 

 


Option 1)

30 cm towards the mirror

This is incorrect

Option 2)

36 cm away from the mirror

This is correct

Option 3)

30 cm away from the mirror

This is incorrect

Option 4)

 36 cm towards the mirror

This is incorrect

Posted by

Plabita

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