Question

A child staying in a coastal region tests the drinking water and the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Explain the reason for it.

Answer 1

Hint:Water is considered as a good conductor of electricity. Actually, it is the impurities in water which makes it a conductor of electricity. The deflection of the compass needle depends on the ability of the water to conduct electricity.

Complete step by step answer.
Step 1: Mention how seawater is different from drinking water to figure out the reason for more deflection in the case of seawater.
The child must have wound a current-carrying wire around the magnetic compass and placed it in the drinking water and the seawater to test them both. He then observed more deflection in the needle when it was placed in seawater than when it was placed in the drinking water.

Electricity is conducted by the movement of electric charges or ions. Seawater is rich in impurities (ions) while drinking water is a processed form of water and has lesser impurities (ions). Since more impurities imply better conduction of electricity, the seawater will be a better conductor than the drinking water. Thus more deflection of the compass needle is obtained for the seawater.

Additional information:We are often advised not to touch electrical sockets or outlets with wet hands because water is a good conductor of electricity. Pure water is free of impurities and so it will be a poor conductor of electricity. But tap water contains small amounts of salt in it and thus will conduct electricity very well.

Note:The conduction of electric current in the wire wounded around the compass will induce a magnetic field. This then causes the compass needle to rotate or deflect. So greater the current means greater is the magnetic field and thus more will be the deflection of the needle. The majority of impurities in seawater is made up by the dissolved salt in it.