Question

A. Define the term ‘self-inductance’ and write its S.I. unit.
B. Obtain the expression for the mutual inductance of two long co-axial solenoids and would one over the other, each of length L and radii and and and number of turns per unit length, when a current I is set up in the outer solenoid

Answer 1

A measure or coefficient of self-induction in a circuit, usually measured in henries. henry is the sI unit .
hope it helps u

Answer 2

A) Self induction is an electromagnetic induction in which varying current of a       current carrying conductor induces a voltage in the same conductor.

• The varying current of the circuit creates a magnetic field which induces a voltage in the same circuit.
• Induced voltage,V=N dφ/dt

         where N is the number of turns in the coil and dφ/dt is the rate of change of flux

• Henry (H) is the unit of self inductance.
• 1 H= 1 Volt/ampere/second

B) Let N1 and N2 be the number of turns of inner and outer solenoid. r1 and r2 be their radius and I2 be the current through outer coil.

• Total flux in the inner solenoid

• N1φ1 =M12 I2

• Also,

• N1φ1 =(μ0πn1n2$r1^{2}$l) I2

• $M_{12}$ = N1φ1/I2  =  μ0πn1n2$r1^{2}$l

• $M_{21}$ = N2φ2/I1  =  μ0πn1n2$r1^{2}$l