Friday, 25 January 2019
Q. Why are the electrovalent compounds dissociated when dissolved in water?
answer. The electrovalent compounds remain bound together by electrostatic force. This force becomes weaker in the water medium.
Q. Write two characteristics of fuse wire.
Answer. Two characteristics of fuse wire are given below
(a) Fuse wire should have high resistance.
(b) Melting point of fuse wire should be low.
Q. Why is a resistance called the starting resistance connected in series with the armature coil of a motor?
Answer. The back emf produced is minimum at the start and thus current through the armature is maximum at the beginning and this current at the start may be so large that armature coil may got burnt. So a resistance called 'the starting resistance' is connected in series with the armature coil.
Q. Can a DC dynamo act as a DC motor?
Answer. A DC motor is exactly similar in construction to a DC dynamo, having a field magnet, a commutator and an armature. Thus a D.C dynamo may act as a DC motor when the current from an external DC source is led to the commutator through carbon brushes, from where the current flows to the armature coil and the DC motor starts working.
Q. Why is the core of a transformer laminated?
Answer. The core is laminated to reduce the effect of eddy currents.
Q. Why does a spark appear at the switch when a circuit containing a coil is switched off.
Answer. When the circuit is switched off, the current begins to fall off very quickly and therefore, a corresponding large back emf is induced which tends to maintain the current. The induced emf is usually large enough to break the insulation of the air gap of the switch and so a spark is produced.
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