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Electric Circuit

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Electric Circuit - Lesson Summary

Electricity needs a path to flow from the positive terminal to the negative terminal of an electric cell.   A connection that provides a path outside an electric cell, for the electricity to flow from the positive terminal to the negative terminal of the cell, is called an electrical circuit. For example, a bulb glows only when the positive terminal and the negative terminal of an electric cell are connected to the two terminals of the bulb. If the wires from the bulb are connected to the same terminal (either positive or negative), then the bulb does not glow. Sometimes, the bulb may not glow even though the connections are properly made. This may be because the flow of electricity is incomplete as the filament in the bulb is broken. A bulb with broken filament is said to be fused.

A device that is used to stop the flow of electricity by breaking the circuit is called a switch. Switches have wide range of applications. Some common types of switches are:
     •  Toggle switches, which are used in our houses.
     •  Pushbutton switches, which are used in the starter of a water pump.
     •  Joystick switches, which are used in the remote control unit of a toy car.


Electric circuit including a switch


Activity 1: 

To connect a bulb to an electric cell, we will need:
  • Four pieces of wire and 
  • An adhesive tape



First, remove the plastic insulation from the ends of all the four wires, such that a small length of the metal wire is exposed.

Fix the exposed end of one wire to the positive terminal of the cell. Fix the exposed end of another wire to the negative terminal of the cell. Now, fix the exposed ends of the other two pieces of the wires to the two terminals of a bulb with the adhesive tape. This is what the bulb and the electric cell will look like with the wires attached to them.

We now connect one of the wires of the bulb to a wire from the electric cell.  Then we connect the second wire from the bulb to the remaining wire from the electric cell. The bulb now starts glowing.

Activity 2: 

Let’s connect all the wires to the positive terminal of the cell now.  The bulb still doesn’t glow. It is because the connection should be made in a specific way for the bulb to glow. Now let’s reconnect it, the way we connected the first time. The bulb glows again. Electricity needs a path to pass from the positive terminal to the negative terminal of the cell. 

When the positive and the negative terminals of an electric cell are connected to the two terminals of a bulb, the path is completed and the bulb glows. 

A connection that provides a complete path for the electricity to pass from the positive terminal of the cell to its negative terminal, outside an electric cell, is called an electrical circuit.

At times a bulb in the circuit will not glow even though the connections are correct.  The reason could be a fused bulb.

 A bulb is said to have fused when its filament breaks. When the filament is broken, there is a break in the flow of electricity through the terminals of the bulb. That is, the path required by electricity to flow is broken. Hence, the bulb does not glow.

We need to disconnect one of the wires to switch off the bulb in the circuit that we just made. But then we’ll need to reconnect the wire manually to get the bulb to glow again. A switch in the circuit will make it easy to switch the bulb on and off.

A switch is a device that is used to stop the flow of electricity by breaking the circuit. A switch enables us to break or complete a circuit on the click of a button. 

Making a switch:

We need the followingt to construct an electric switch thermocol piece,
  • A pair of thumbtacks,
  • A metal paper clip,
  • Four pieces of insulated wire, 
  • An electric cell and 
  • A torch bulb.
    
    
    We start by creating the circuit. There will be one difference, though. We will leave one of the wires of the electric cell and the bulb unconnected.
  • We connect one end of the loose wire from the cell to a thumbtack, which is fixed on the thermocol.
    
    Now we connect one end of the loose wire from the bulb to another thumbtack fixed to the thermocol close to the thumbtack fixed earlier. 
    
    The distance between the two thumbtacks should be less than the length of the paper clip. The switch is ready.
    
    When we want to switch the bulb on, just bring the paper clip in contact with the thumbtack.
    
    This completes the circuit and the bulb starts glowing. To click it off, take the clip away from the thumbtack.
    
    Switches can be found in a variety of applications. A few common types of switches are:
    
    
  • Toggle switch
  • Used in our houses.
  • Pushbutton switch
  • Used in the starter of a water pump.
  • Joystick switch
  • Used in the remote control unit of a toy car.

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