K.C.S.E Physics Q & A - MODEL 2019PP2QN18

K.C.S.E Physics Q & A - MODEL 2019PP2QN18

(ii) Describe how a magnet can be demagnetised using the electrical method. 
(b) You are provided with two iron bars P and Q. One of the bars is magnetized while the other is not. Explain how themagnetized bar can be identified without using a magnet or magnetic material. 
(c)Figure 12 shows two identical copper coils X and Y placed close to each other. Coil X is connected to a DC power supply while coil Y is connected to a galvanometer.

​Explain what is observed on the galvanometer When the Switch is closed.
(ii) State What is observed on the galvanometer when the switch is opened. 
(iii) State what wou1d be observed if the number of turns in coil Y is doubled.

answers

​(a) Place the bar magnet inside a solenoid placed in the an East-West direction then pass an alternating current through the solenoid 
(b) Suspend each of the bars through its center of gravity and set it swinging in a horizontal plane shows a vertical axis through its centre
The magnetized bar will always come to rest in a north-south direction
(c) (i) The galvanometer pointer first deflects then moves back when the switch is closed a current builds up in a coil X and due to change influx linkage an emf is induced in coil Y making an induced current to flow through the galvanometer  during the time current in coil X is rising. When current through coil X is steady no induced current flows through the galvanometer since there is no change in flux linkage
Therefore pointer deflects back
(ii) Pointer deflects in the opposite direction.
(iii) Magnitude of deflection increases