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Program for focal length of a lens
  • Last Updated : 12 Apr, 2021
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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 : 
 

\frac{1} {F} = \frac {1}{O} + \frac{1}{I}

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 <iostream>
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




<?php
// PHP program to determine
// the focal length of a lens
// Function to determine the
// focal length of a lens
function 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;
 
    echo "Focal length of a lens is "
        , focal_length($image_distance,
                      $object_distance)
        , " units .";
 
// This code is contributed by anuj_67.
?>

Javascript




<script>
 
// javascript program to determine
// the focal length of a lens
 
// Function to determine the focal
    // length of a lens
    function focal_length(image_distance,
                              object_distance)
    {
        return 1 / ((1 / image_distance) +
                           (1 / object_distance));
    }
   
 
// Driver Function
 
         // variable to store the distance
        // between the lens and the image
        let image_distance = 2;
   
        // variable to store the distance
        // between the lens and the object
        let object_distance = 50;
           
        document.write("Focal length of a lens is "
        + focal_length(image_distance, object_distance)
                                         + " units.");
            
</script>

Output : 

Focal length of a lens is 1.92308 units . 

 

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