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

The mass of the lift is 200 kg , when it ascends with an acceleration of $4 \mathrm{~m} / \mathrm{s}^2$ then the tension in the cable supporting the lift will be [Given: Acceleration due to gravity $g=10 \mathrm{~m} / \mathrm{s}^2$ ]