Which of the following is the Lens maker’s formula?
1
\(\frac{1}{f}\; = \;\frac{{\left( {{n_2} + {n_2}} \right)}}{{{n_1}}}\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\)
2
\(\frac{1}{f}\; = \;\frac{{\left( {{n_2} - {n_1}} \right)}}{{{n_1}}}\left( {\frac{1}{{{R_1}}} + \frac{1}{{{R_2}}}} \right)\)
3
\(\frac{1}{f}\; = \;\frac{{\left( {{n_2} - {n_1}} \right)}}{{{n_1}}}\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\)
4
\(\frac{1}{f}\; = \;\left( {{n_2} - {n_1}} \right)\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)\)