Question

An object placed at 20 cm from the pole of concave mirror it forms and real image at a distance of 60 cm from the pole. Find the focal length of mirror.

Answer 1

Question : An object placed at 20 cm from the pole of concave mirror it forms and real image at a distance of 60 cm from the pole. Find the focal length of mirror ?


Answer :


In this Question Theoretically Given that , An object placed at 20 cm from the pole of concave mirror it forms and real image at a distance of 60 cm from the pole.


Given :

✏ Object Distance = -20 Centimeters

✏ Image Distance = 60 Centimeters



To Find : What is the Focal Length of Concave Mirror ?


For Find Focal Length of Concave Mirror , We should be know about "Mirror Formula".


✒ Mirror Formula = A Formula which Gives Relationship between object distance (u) , Image Distance (v) and Focal Length (f) that is called "Mirror Formula".




Mirror Formula = 1/f = 1/u + 1/v


We have: ✏ Object Distance = -20 Centimeters

✏ Image Distance = 60 Centimeters

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Mirror Formula = 1/f = 1/u + 1/v

➡ 1/f = 1/-20 + 1/60

➡ 1/f = -3 + 1/60

➡ 1/f = -2/60

➡ -2f = 60

➡ f = 60/-2

➡ f = -30


Therefore, Value of Focal Length is (-30) Centimeters.



Hence, Focal Length of Concave Mirror is -30 Centimeters

Answer 2

Given :

Object Distance = -20 Cm

Image Distance = 60 Cm







Mirror Formula =) A Formula which gives relationship between object distance Image Distance and Focal Length that is called Mirror Formula.




Mirror Formula =) 1/f = 1/u + 1/v



_____



=> 1/f = 1/-20 + 1/60

=> 1/f = -3 + 1/60

=> 1/f = -2/60

=> -2f = 60

=> f = -60/2

=> f = -30 Centimeters



Therefore Focal Length is -30 Centimeters