When two co-axial coils having same current in same direction are bring close to each other then what effect on the value of current in both coils ? and Why?

Flux linked through following coils changes with respect to time then for which coil an emf is not induced

1 copper coil

2. wooden coil

3. iron coil

4. none

A solenoid has the self inductance 2H. If length of the solenoid is doubled having turn density and area constant then new self inductance is

1. 4H

2. 1H

3. 8H

4. 0.5H

A solenoid is wound over a rectangular frame. If all the linear dimensions of the frame are increased by a factor 3 and the number of turns per unit length remains the same, the self induction increased by a factor of

1. 3

2. 9

3. 27

4. 63