Answer & explanation
Correct answer: option 3
$ V = \frac{1240}{\lambda} -\frac{\phi}{e}$
$ V_1 - V_2 = \frac{1240}{\lambda_1} - \frac{1240}{\lambda_2} = \frac{1240}{300} - \frac{1240}{400}= 1V$
Correct answer: option 3
$ V = \frac{1240}{\lambda} -\frac{\phi}{e}$
$ V_1 - V_2 = \frac{1240}{\lambda_1} - \frac{1240}{\lambda_2} = \frac{1240}{300} - \frac{1240}{400}= 1V$