In a vibrating string with fixed ends the waves are of type

The focal length of combination of lenses formed with lenses having power of +2.50 D and $-3.75$ D will be

The current flowing in a coil is 3 A and the power consumed is 108 W . If the a.c. source is of $120 \mathrm{~V}, 50 \mathrm{~Hz}$, the resistance in the circuit is

In the following circuit, the current flowing through zener diode is