Question

why the induced emf in a coil opossing the cause which is producing it. why not the induced emf aids the cause 

Answer 1

It is as per Lenz law which states that effect opposes the cause.
If it will not oppose then law of conservation of energy with be defied .

Assume that a magnet is brought near a coil. Emf will be induced.It means energy is generated.From where that energy is generated?
It is taken from the kinetic energy of the magnet and get slows down ,i.e, induced emf opposes cause.