Q18 of 24 Page 369

What is solenoid? What does the divergence of magnetic field lines near the ends of a current-carrying straight solenoid indicate?

A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.
The divergence of magnetic field lines near the ends of a current-carrying straight solenoid indicate a decrease in the magnetic field strength near the ends of the solenoid.

Fig.: Magnetic field lines around a current carrying solenoid

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16

Two coils 1 and 2 of insulated copper wire having large but different number of turns are wound over a cardboard cylinder. Coil 1 is connected to battery and a plug key. Coil 2 is connected to a galvanometer.
How will the galvanometer reading change when

(i) key is plugged in and


(ii) key is taken out? Give reason for your answer in each case.

 17

Under what conditions permanent electromagnet is obtained if a current carrying solenoid is used? Support your answer with the help of a labelled circuit diagram.

 19

How will the magnetic field produced at a point P by a current carrying-circular coil change if we increase the

i. value of current flowing through the coil,


ii. distance of the point P from the coil,


iii. number of turns of the coil?

 20

Shown in the given diagrams (a), (b) and (c) are the magnetic fields around different systems. Identify them. Compare the pattern of the field lines in all the three systems.