# Program for focal length of a lens

Write a program to determine the focal length of a lens.

Focal length is the distance between the center of the lens to the principal foci. In order to determine the focal length of a lens we should know the distance between the lens and the image ( I ) and the distance between the lens and the object ( O ). Here, we will use the lens equation also called the focal length equation.

The lens equation is : = + here,
F is the focal length
I is the distance between the lens and the image
O is the distance between the lens and the object

Examples :

Input : O = 50, I = 2
Output : F = 1.92308

Input : O = 25, I = 5
Output : F = 4.16667


## C++

 // C++ program to determine  // the focal length of a lens  #include  using namespace std;     // Function to determine the focal length of a lens  float focal_length(float image_distance, float object_distance)  {      return 1 / ((1 / image_distance) + (1 / object_distance));  }     // Driver function  int main()  {      // variable to store the distance      // between the lens and the image      float image_distance = 2;         // variable to store the distance      // between the lens and the object      float object_distance = 50;         cout << "Focal length of a lens is "          << focal_length(image_distance, object_distance)           << " units .";         return 0;  }

## Java

 // Java program to determine  // the focal length of a lens     import java.io.*;     class GFG {         // Function to determine the focal      // length of a lens      static float focal_length(float image_distance,                                float object_distance)      {          return 1 / ((1 / image_distance) +                              (1 / object_distance));      }         public static void main(String[] args)      {             // variable to store the distance          // between the lens and the image          float image_distance = 2;             // variable to store the distance          // between the lens and the object          float object_distance = 50;                     System.out.println("Focal length of a lens is "         + focal_length(image_distance, object_distance)                                           + " units.");      }  }     // This code is contributed by Ajit.

## Python3

 # Python3 program to determine  # the focal length of a lens     # Function to determine the focal length of a lens  def focal_length(image_distance, object_distance)      : return 1 / ((1 / image_distance) + (1 / object_distance))     # Driver Code  # Variable to store the distance  # between the lens and the image  image_distance = 2    # Variable to store the distance  # between the lens and the object  object_distance = 50    result = focal_length(image_distance, object_distance)  print("Focal length of a lens is ", result, " units.")

## C#

 // C# program to determine  // the focal length of a lens  using System;     class GFG {         // Function to determine the focal      // length of a lens      static float focal_length(float image_distance,                              float object_distance)      {          return 1 / ((1 / image_distance) +                       (1 / object_distance));      }             // Driver code      public static void Main()      {             // variable to store the distance          // between the lens and the image          float image_distance = 2;             // variable to store the distance          // between the lens and the object          float object_distance = 50;                     Console.WriteLine("Focal length of a lens is "         + focal_length(image_distance, object_distance)                                          + " units.");      }  }     // This code is contributed by Vt_m.

## PHP

 

Output :

Focal length of a lens is 1.92308 units .


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