# Program to determine focal length of a spherical mirror

Write a program to determine the focal length of a spherical mirror.

Focal length is the distance between the center of the mirror to the principal foci. In order to determine the focal length of a spherical mirror we should know the radius of curvature of that mirror. The distance from the vertex to the center of curvature is called radius of curvature.

The focal length is half the radius of curvature.
Formula :

```F =   ( R / 2 )      for concave mirror
F = - ( R / 2 )      for convex mirror```

Examples :

```For a convex mirror
Input : R = 30
Output : F = 15

For a convex mirror
Input : R = 25
Output : F = - 12.5
```

## C++

 `// C++ program to determine ` `// the focal length of a ` `// of a spherical mirror ` `#include ` `using` `namespace` `std; ` ` `  `// Determines focal length ` `// of a spherical concave ` `// mirror ` `float` `focal_length_concave(``float` `R) ` `{ ` `    ``return` `R / 2 ; ` `} ` ` `  `// Determines focal length of a  ` `// spherical convex mirror ` `float` `focal_length_convex(``float` `R) ` `{ ` `    ``return` `- ( R / 2 ) ; ` `} ` ` `  `// Driver function ` `int` `main() ` `{ ` `    ``float` `R = 30 ;      ` `    ``cout << ``"Focal length of spherical"` `         ``<< ``"concave mirror is : "` `         ``<< focal_length_concave(R)  ` `         ``<< ``" units\n"``; ` `    ``cout << ``"Focal length of spherical"` `         ``<< ``"convex mirror is : "` `         ``<< focal_length_convex(R)  ` `         ``<< ``" units"``; ` `    ``return` `0; ` `}  `

## Java

 `// Java program to determine ` `// the focal length of a ` `// of a spherical mirror ` `import` `java.util.*; ` `import` `java.lang.*; ` ` `  `public` `class` `GfG{ ` `    ``// Determines focal length ` `    ``// of a spherical concave ` `    ``// mirror ` `    ``public` `static` `float` `focal_length_concave(``float` `R) ` `    ``{ ` `        ``return` `R / ``2` `; ` `    ``} ` ` `  `    ``// Determines focal length of a  ` `    ``// spherical convex mirror ` `    ``public` `static` `float` `focal_length_convex(``float` `R) ` `    ``{ ` `        ``return` `- ( R / ``2` `) ; ` `    ``} ` `     `  `    ``// Driver function ` `    ``public` `static` `void` `main(String argc[]) ` `    ``{ ` `        ``float` `R = ``30` `; ` `         `  `        ``System.out.print(``"Focal length of"` `+ ` `                         ``"spherical concave"``+ ` `                         ``"mirror is : "``+ ` `                         ``focal_length_concave(R) + ` `                         ``" units\n"``); ` `                         `  `        ``System.out.println(``"Focal length of"``+ ` `                           ``"spherical convex"``+  ` `                           ``"mirror is : "``+ ` `                           ``focal_length_convex(R) +  ` `                           ``" units"``); ` `    ``} ` `} ` ` `  `/* This code is contributed by Sagar Shukla */`

## Python

 `# Python3 program to determine ` `# the focal length of a ` `# of a spherical mirrorr  ` ` `  `# Determines focal length of  ` `# a spherical concave mirror ` `def` `focal_length_concave(R): ` `    ``return` `R ``/` `2` ` `  `# Determines focal length of ` `# a spherical convex mirror ` `def` `focal_length_convex(R): ` `    ``return` `-` `( R``/` `2` `)  ` ` `  `# Driver function ` `R ``=` `30` `; ` `print``(``"Focal length of spherical concave mirror is :"``, ` `        ``focal_length_concave(R),``" units"``) ` `print``(``"Focal length of spherical convex mirror is : "``, ` `        ``focal_length_convex(R),``" units"``) `

## C#

 `// C# program to determine the focal  ` `// length of a of a spherical mirror ` `using` `System; ` ` `  `class` `GfG { ` `     `  `    ``// Determines focal length of a  ` `    ``// spherical concave mirror ` `    ``public` `static` `float` `focal_length_concave(``float` `R) ` `    ``{ ` `        ``return` `R / 2 ; ` `    ``} ` ` `  `    ``// Determines focal length of a  ` `    ``// spherical convex mirror ` `    ``public` `static` `float` `focal_length_convex(``float` `R) ` `    ``{ ` `        ``return` `- ( R / 2 ) ; ` `    ``} ` `     `  `    ``// Driver function ` `    ``public` `static` `void` `Main(String[] argc) ` `    ``{ ` `        ``float` `R = 30 ; ` `        ``Console.Write(``"Focal length of"` `+ ` `                      ``"spherical concave"` `+ ` `                      ``"mirror is : "` `+ ` `                      ``focal_length_concave(R) + ` `                      ``" units\n"``); ` `                         `  `        ``Console.Write(``"Focal length of"` `+ ` `                      ``"spherical convex"` `+  ` `                      ``"mirror is : "` `+ ` `                      ``focal_length_convex(R) +  ` `                      ``" units"``); ` `    ``} ` `} ` ` `  `/* This code is contributed by parashar */`

## PHP

 ` `

Output :

```Focal length of spherical concave mirror is 15 units
Focal length of spherical convex mirror is -15 units```

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