A long straight wire carries a current, I = 2 ampere. A semi-circular conducting rod is placed beside it on…

A long straight wire carries a current, I=2 ampere. A semi-circular conducting rod is placed beside it on two conducting parallel rails of negligible resistance. Both the rails are parallel to the wire. The wire, the rod and the rails lie in the same horizontal plane, as shown in the figure. Two ends of the semi-circular rod are at distances 1 cm and 4 cm from the wire.  At time t=0, the rod starts moving on the rails with a speed v=3.0 m s-1 (see the figure).

A resistor R=1.4 Ω and a capacitor C0=5.0 μF are connected in series between the rails. At time t=0C0 is uncharged. Which of the following statement(s) is (are) correct? [μ0=4π×107 SI units. Take ln2=0.7]

  1. Maximum current through R is 1.2×106 ampere
  2. Maximum current through R is 3.8×106 ampere.
  3. Maximum charge on capacitor C0 is 8.4×1012 coulomb.
  4. Maximum charge on capacitor C0 is 2.4×1012 coulomb.

Solution

Magnetic field due the long wire, B=μ0I2πx

Motional emf in small element, 

dε=Bvdx=3μ022πxdx

ε=3μ0π141xdx

  ε=3μ0πln4=16.8×107

Maximum charge on capacitor, 

qmax=εC

=16.8×1075×106

=84×1013 C=8.4×1012 C

Maximum current in circuit, 

Imax=εR=16.8×1071.4

=1.2×10-6 A

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Asked in: JEE Advanced 2021 (Paper 1)

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