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SAI INTERNATIONAL SCHOOL

                                                    CLASS - VIII

                                              Subject – CHEMISTRY

                        Chapter – CHEMICAL EFFECT OF ELECTRIC CURRENT
                   TOPIC – LED (Light Emitting Diode), Effects of Electric Current



                                                  LESSON NOTES



        DETECTION  OF  WEAK  ELECTRIC  CURRENT  FLOWING  THROUGH  A  CONDUCTING
        LIQUID:


              The current flowing in an electric circuit is usually detected by using a small electric bulb.
              When an electric current flows through the electric bulb, due to the heating effect of current,

               the filament of the bulb gets heated up and glows to produce light.

              But, when the current flowing through the circuit is too weak, the heating effect is also too
               small,  due  to  which  the  filament  does  not  get  heated  up  sufficiently  and  the  bulb  glows

               dimly.
              Therefore, an electric bulb or a torch bulb cannot be used to detect weak electric current

               flowing through a liquid in a circuit.
              So, the weak electric current flowing through liquids can be detected in two ways:

                   a)  By using a LED (Light Emitting Diode)

                   b)  By using a Magnetic Compass



            a)  By using a LED:
                     We can use LED (light-emitting diode) in place of a torch bulb, for detecting weak

                       electric current passing through a liquid.

                     LED is a semi-conductor device which glows even when a very weak current passes
                       through it.

                     There are two wires, called Leads, attached to an LED, where, one lead is slightly

                       longer than the other.
                     While connecting LED in the circuit, in place of a bulb, the longer lead is connected

                       to the positive terminal of the battery and the shorter lead is connected to the
                       negative terminal of the battery.





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