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Magnetic flux passing through a coil is ...

Magnetic flux passing through a coil is initially `4xx 10^-4` Wb. It reduces to 10% of its original value in t second. If the emf induced is 0.72 mV then t in second is

A

`0.3`

B

`0.4`

C

`0.5`

D

`0.6`

Text Solution

Verified by Experts

The correct Answer is:
C
`phi_(1)=4xx10^(-4)Wb,phi_(2)=0.4xx10^(-4)Wb,e=0.72mV,dt=?`
Now, `e=(dphi)/(dt)=(phi_(1)-phi_(2))/(dt)`
`:.dt=(phi_(2)-phi_(2))/(e)=(4xx10^(-4)-0.4xx10^(-4))/(0.72xx10^(-3))`
`=(3.6)/(7.2)=(1)/(2)=0.5sec.`
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