A magnetic compass needle is placed in the plane of paper near point A as shown in Figure 13.6. In which plane should a straight current carrying conductor be placed so that it passes through A and there is no change in the deflection of the compass? Under what condition is the deflection maximum and why?

Ans. In the plane of the paper itself. The axis of the compass is vertical and the field due to the conductor is also vertical. It could result in a dip of compass needle which is not possible in this case (dips result only if axis of compass is horizontal). The deflection is maximum when the conductor through A is perpendicular to the plane of paper and the field due to
it is maximum in the plane of the paper.

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.
Ans. Following conditions are necessary for making electromagnet from a current carrying
solenoid.
 (a) Circuit should be closed.
 (b) A core of soft iron should be used. 

According to Right Hand Thumb Rule, if all fingers of right hand we wrapped in a fist and thumb shows the direction of electric current, then direction of wrapped fingers shows the direction of magnetic field. In case of r1, the direction of magnetic field is towards the paper. In case of r2, the direction of magnetic field is out of the paper. Since r1 > r2, so strength of magnetic field at P is less than that at Q.

The deflection increases. The strength of magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

(i) Yes, Alpha particles being positively charged constitutes a current in the direction of motion.
(ii) No. The neutrons being electrically neutral constitute no current.

The thumb indicates the direction of current in the straight conductor held by curled fingers, whereas the Fleming’s left-hand rule gives the direction of force experienced by current carrying conductor placed in an external magnetic field.

Strength of the magnetic field falls as distance increases. This is indicated by the decrease in degree of closeness of the lines of field.

The divergence, that is, the falling degree of closeness of magnetic field lines indicates the fall in strength of magnetic field near and beyond the ends of the solenoid