A constant current \(i\) is maintained in a solenoid. Which of the following quantities will increase if an iron rod is inserted in the solenoid along its axis?

Choose the correct option: 
1. (a), (b), (c)
2. (b), (c)
3. (c), (d)
4. (a), (b), (d)

Two solenoids have identical geometrical construction but one is made of thick wire and the other of thin wire. Which of the following quantities are different for the two solenoids?

(a) self-inductance
(b) rate of Joule heating if the same current goes through them
(c) magnetic field energy if the same current goes through them
(d) the time constant if one solenoid is connected to one battery and the other is connected to another battery

Choose the correct option 

1. (a), (b)

2. (b), (d) 

3. (c), (d)

4. (a), (d)