When the current in one coil changes at a rate of 5.0 a/s, an emf of −4.0 ✕ 10−3 v is induced in a second, nearby coil. what is the mutual inductance of the two coils (in h)?

Explanation:

As per the condition of mutual inductance of the coil we know that flux linked with coil 2 is proportional to the current in the coil 1

so here we will have

here we know that rate of change in flux is equal to the EMF induced in the coil

so we will have

so we have

now plug in all values in it

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me