Suppose the loop is stationary but the current feeding the electromagnet that produces the magnetic field is gradually reduced so that the field decreases from its initial value of 0.3 T at the rate of 0.02 T `s^(-1)`. If the cut is joined and the loop has a resistance of 1.6 `Omega`, how much power is dissipated by the loop as heat ? What is the source of this power ?

Explanation

Induced emf,
`epsilon=-(dphi)/(dt)`
`therefore epsilon=-d/(dt)(AB cos 0^@)(because vecA||vecB)`
`=-A(dB)/(dt)`
`=-(8xx10^(-2)xx2xx10^(-2))(-0.02)`
`therefore epsilon=3.2xx10^(-5)` V
Power dissipated in the form of heat,
`P=epsilon^2/R`
`=(3.2xx10^(-5))^2/1.6`
`therefore P=6.4xx10^(-10)W` (watt)
Magnetic field changing with time is an external source to produce this power.