Your elders might have cautioned
you against touching an electrical
appliance with wet hands. But
do you know why it is dangerous to
touch an electrical appliance with wet
We have learnt earlier that the materials, which allow electric current to pass through them, are good conductors of electricity. On the other hand, materials, which do not allow electric current to pass through them easily, are poor conductors of electricity.
Join the free ends of the tester together for a moment. This completes the circuit of the tester and the bulb should glow. However, if the bulb does not glow, it means that the tester is not working. Can you think of the possible reasons? Is it possible that the connections are loose? Or, the bulb is fused? Or, your cells are used up? Check that all the connections are tight. If they are, then replace the bulb with another bulb. Now test if the tester is working or not. If it is still not working then replace the cells with fresh cells.
In Class VII, we have learnt some effects
of electric current. Can you list these
effects? What effect does the current
produce when it flows through a
conducting solution? Let us find out.
Take out carbon rods carefully from two discarded cells. Clean their metal caps with sand paper. Wrap copper wires around the metal caps of the carbon rods and join them to a battery (Fig. 14.5). We call these two rods electrodes. (Instead of carbon
Recall that a brand new bicycle has shiny
handlebar and wheel rims. However, if
these are accidentally scratched, the
shiny coating comes off revealing a not
so shiny surface beneath. You might
have also seen women using ornaments,
which appear to be made of gold.
However, with repeated use, the gold
coating wears off, revealing silver or some
other metal beneath.
In both these cases, a metal has a coating of another metal. Do you wonder how a layer of one metal can be deposited on top of another? Well, let us try doing it ourselves.