PHYSICS [3 Mark Question Answer]

(a) P will have a positive charge
(b) Q will have no charge.
(c) The Cap of the electroscope will have no charge.
(d) The gold leaf will have a negative charge.
(e) The leaf will diverse because like charges repel each other
(f) If electroscope is earthed then the metal rod will have a positive charge.

The simple experiment to show that like poles repel while unlike poles attract each other is: Suspend a bar magnet and allow it to freely rotate. When it will come to rest, it will point towards the north-south direction. Now, bring the N pole of the second magnet near the North pole of the suspended magnet, we will see repulsion between the two magnets. But, if we bring south pole of the second magnet near the north pole of a suspended magnet then we will observe attraction. So, we can say like poles repel while unlike poles attract.

The magnetisation of steel needle using electric current: Wind a length of copper wire around a steel needle and connect it to battery and switch. After the current is passed through the copper wire for some time, we will notice that the steel needle got magnetised.

The magnetization of Iron Bar by Single Touch Method: Place the iron piece on the table and stroke it with a bar magnet from A to B with one end of the magnet. When the magnet reaches B it is lifted and brought back to A to repeat the stroke. After a few strokes, we will notice that A has acquired the same polarity as the pole rubbed against it.

Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track as you turn the spindle. The track may be made from carbon, cermet (ceramic and metal mixture), or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually called sliders, are also available.
Variable resistance is a device used to change the resistance and hence the current flowing through a circuit; without changing the voltage.