AC and EMI

1. A coil with inductance L=0.70H and active resistance r=20Ω is connected in series with an inductance-free resistance R. An alternating voltage with effective value V=220V and frequency ω=314 rad/s is applied across the terminal of this circuit.

i) The value of resistance R for which the maximum heat power is generated in the circuit is

A) 22 KΩ B) 2.2KΩ C) 0.2KΩ D) 220KΩ

2. A rectangular frame ABCD, made of uniform metal wire has a straight connection between E and F made of the same wire, as shown in the figure. AEFD is a square of side 1m, and EB=FC=0.5m. The entire circuit is placed in a steadily increasing, uniform magnetic field directed into the plane of the paper and normal to it. The rate of change of magnetic field is 1 T/s. The resistance per unit length of the wire is 1Ω/m.

i) Current in segment AE is
A) 122 A B) 722 A C) 622 A D) 822 A

ii) Net current in the segment EF is
A) 122 A B) 222 A C) 322 A D) 422 A