Hiwhat We Need Is What We Get

Topics: Water, Electric charge, Sodium chloride Pages: 3 (825 words) Published: August 13, 2013
K.R.Mangalam World School
South City-I, Gurgaon
Class-VIII Sub.-Chemistry (Chemical Effects of Electric Current)

EXTRA QUESTIONS:
Q. Why the bulb glows when the electric current passes through it? Ans. Due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing. Q. Write a short note on:

(a) LED
Ans. LED- Light Emitting Diodes are used for lighting.
There are two wires(called leads) attached to a LED. One lead is longer than the other. Longer lead- connected to positive terminal of battery
Shorter lead- connected to negative terminal of battery
Advantages over CFL- LEDs consumes less electricity
LEDs glow even in weak current
CFL contain mercury which is toxic and hence CFLs require safe disposal

Disadvantages over CFL- LEDs are expensive

Q. Ionic compounds do not conduct electricity in solid form but their aqueous solution conduct electricity. Why? Or
Common salt does not conduct electricity but its aqueous solution conduct electricity. Why? Ans. Ionic compounds (e.g.- Common salt) have strong electrostatic forces of attraction between their constituent ions. Thus ions are strongly held and cannot move. Therefore, cannot conduct electricity. Aqueous solution means solution prepared by dissolving in water. Water has a high dielectric constant(ability to screen charges or ability to separate opposite ions in ionic compounds) and thus diminish the attraction of the two opposite charges. Ions are now free to move and thus conduct electricity.

NCERT QUESTIONS:
Q. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason? Ans. The magnetic or compass needle shows deflection due to magnetic effect of electric current. This proves that the given solution is a conducting solution as circuit is complete and current is flowing through the wire wrapped around magnetic compass resulting in deflection of magnetic...
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