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Page 65 - CT&AI_CLasa_7_Part_1
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    Why does the lamp fail to glow?                      the spring and the battery, the light goes out.
                                                  (Abstract Thinking)         This is most similar to which problem?

                                (a)   The  lamp failed  to  glow  because                           (Pattern Recognition)
                                   the switch was faulty.                           (a)  A broken filament in the bulb

                                (b)   Rubber is  an insulator and it                (b)   Using a battery with the wrong
                                   prevents current from flowing                       voltage
                                   between the wire and the terminal.
                                                                                    (c)   Having insulation (non-conductor)
                                (c)   Insulation  does  not affect current             blocking the path

                                   flow  and the problem  must be a
                                                                                    (d)  The switch being clicked too hard
                                   dead battery.
                                                                           7.  Tanya connects two cells in series to power an
                                (d)   The bulb  needs  more voltage  to       LED. She closes the switch but the LED does
                                   start glowing.                             not  glow.  The LED's shorter wire (negative

                      5.  The  '+'  and  '−'  markings  on  a  battery  have   terminal) connects to the positive end of the
                         been  scratched  off and are unreadable.             battery and the longer wire (positive terminal)
                         Meena  must  identify  which terminal  is            connects to the negative end.
                         positive and which is negative. She has: one         Why does the LED not glow, and which wires
                         LED (with  clearly visible  longer and shorter       must be swapped to fix it?
                         wires), connecting wires, and a small bulb.                                (Algorithmic Thinking)
                         Design the simplest method using an LED to                 (a)   The LED needs three cells — two are
                         identify the battery terminals, and explain the               insufficient.
                         logic behind it.      (Algorithmic Thinking)
                                                                                    (b)   The LED is connected with reversed
                                (a)   Hold the LED  close  to the battery
                                   terminals.  Check    which   side                   polarity; swap the two LED wires so
                                   appears brighter. Use this to decide                the longer wire (+) connects to the
                                   the positive terminal.                              battery's positive end and shorter
                                                                                       wire (−) to the negative end.
                                (b)   Connect  the  LED; if it  glows, the
                                                                                    (c)   The cells are in the wrong order —
                                   terminal  joined  to  the  longer
                                                                                       positive of cell 1 should connect to
                                   wire is positive; if not, reverse the
                                                                                       positive of cell 2.
                                   connections.
                                                                                    (d)   The LED is broken — LEDs in series
                                (c)   Touch both terminals together  —
                                   sparks will come from the positive                  with two cells always burn out.
                                   side.                                   8.  You have six cells (A–F),  some are working,
                                                                              some are dead and only one bulb, one switch,
                                (d)   Use a magnet  to  detect  which         and connecting wires. You must test all the six

                                   terminal is positive.                      cells to find which works, using the minimum
                      6.  In a flashlight, the spring at the bottom must      number of steps. A classmate suggests testing
                         touch the shiny metal part of the battery. If a      two cells at a time in series to save time.
                         piece of paper falls inside and sits between

                                                                             Electricity: Circuits and their Components  63

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