Q.

A rectangular loop of sides 12 cm and 5 cm, with its sides parallel to the x-axis and y-axis respectively, moves with a velocity of 5 cm/s in the positive x-axis direction, in a space containing a variable magnetic field in the positive z-direction. The field has a gradient of 10-3 T/cm along the negative x-direction and it is decreasing with time at the rate of 10-3 T/s. If the resistance of the loop is 6 , the power dissipated by the loop as heat is ______ ×10-9 W.        [2024]


Ans.

(216)

B0 is the magnetic field at origin

dBdx=-10-310-2B0BdB=-0x10-1dx

B-B0=-10-1xB=(B0-x10)

Motional emf in AB=0

Motional emf in CD=0

Motional emf in AD=ε1=B0lv

Magnetic field on rod BC,

B=(B0-(-12×10-2)10)

Motional emf in BC=ε2=(B0+12×10-210)l×v

εeq=ε2-ε1=300×10-7 V

For time variation

(εeq)'=AdBdt=60×10-7 V

(εeq)net=εeq+(εeq)'=360×10-7 V

Power=(εeq)net2R=216×10-9 W