Q18 of 25 Page 13

A compass needle is placed near a current carrying wire. State the observation for the following cases and give reasons for the same in each case.

(A) Magnitude of electric current in the wire is inscreased.


(B) The compass needle is displaced away from the wire. ( CBSE 2007)

(a) Observations : Deflection of the needle inscreases


Reason: Magnetic field strength due tocurrent carrying wire inscreaseas the current in the wire increases i.e B α I


(b) Needle Is displaced away from the wire


Observation: The deflection in the compass needle decreases as it its displacement from the current-carrying wire increases.


Reason: Strength of magnetic field reduces with the inscrease in distanece from the wire as B α 1/R.


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