Section outline

    • Important Terms:

      1. Battery is a combination of two or more cells where a positive terminal of one cell is connected to the negative terminal of the next cell.

      2. Electromagnet is a current carrying coil of an insulated wire wrapped around a piece of iron.

      3. Element is a coil of wire which gets heated when electric current passes through it.

      4. Fuse is a safety device which melts & breaks the circuit when excessive current passes through it, preventing damage to electrical circuits and possible fires.

      5. Electric bulb is device which produces light when an electric current passes through it.

      6. Filament of bulb is a thin wire with high melting point that glows when an electric current passes through it.

      7. Electric cell is a device that converts chemical energy to electrical energy.

      8. Cell holder is a device that holds one or more electric cells (batteries) in place providing electrical contact with the cell terminals.

      9. MCB also known as Miniature Circuit Breaker is an automatically operated switch that protects electrical circuits from damage caused by excess current. 

      10. Closed Circuit is when the switch is in the ‘ON’ position, the circuit from positive terminal of the battery to the negative terminal is complete and the current flows through it.

      11. Open circuit is when the switch is in the ‘OFF’ position, the circuit is incomplete and no current flows through it.

      12. Switch is a device that controls the flow of electricity by breaking or closing an electrical circuit. 

      13. ISI mark is the standard mark assigned by Bureau of Indian Standards, New Delhi for assurance of conformity to the specifications of the products.

      14. Short circuit is sudden flow of very large current due to direct contact of wires.

      15. Overloading is when a many electrical appliances are connected to single socket causing extremely large current to flow.

      Key points:

      1. In the symbol of the electric cell:

      • Longer line represents the positive terminal.
      • Thicker, shorter line represents the negative terminal.

      2. Hans Christian Oersted is the scientist who discovered magnetic effect of electric current.

      3. Electric current always flows from positive to negative terminal in a circuit. 

      4. Fuse wire has low melting point whereas the filament of the bulb has high melting point.

      5. CFL means compact fluorescent lamps.

      6. LED means light emitting diode.

    •  

      Diagrams:
      1. Symbols of electrical components:
      Name Symbol Component
      Electric Cell
      Electric Bulb
      Switch in ON position
      Switch in OFF position
      Battery
      Wire
      2. Closed Circuit:

      3. Open circuit:

      4. Electromagnet:

       
    • Quick Revision Notes
      1. Closed circuit:
      • Switch is in 'ON' position.
      • Circuit is complete.
      • Electric current flows from positive to negative terminal of the battery.
      • Bulb glows.
      2. Open circuit:
      • Switch is in 'OFF' position.
      • Circuit is not complete.
      • Electric current does not flow.  
      • Bulb does not glow.
      3. Effects of electric current:
      • Heating effect
      • Magnetic effect
      4. Types of bulbs & tubes:
      • Incandescent electric bulbs - Emit heat along with light & waste electricity.
      • Fluorescent tube-lights and compact fluorescent lamps (CFLs) - better in saving electricity.
      • Light emitting diode (LED) bulbs  - best &  electricity efficient.
      • Use only ISI mark bulbs, light & tubes.
      5. Short circuit:
      • Direct touching of wires takes place due to damage of insulation or defective wiring.
      • Thus, causing short circuit which causes excessive current to flow through the circuit.
      6. Fuses & MCB's:
      • An electric fuse is a safety device which prevents excessive current from flowing in the electrical circuit.
      • When excessive current flows through the circuit, the fuse wire melts as it has low melting point.
      • This breaks the circuit immediately.
      • MCB's or miniature circuit breakers are used instead of fuse as they automatically turn off when current in a circuit exceeds the safe limit.
      7. Electromagnet:
      • Works on the principle of magnetic effect of electric current.
      • When a piece of iron is wrapped with a current carrying coil of insulated wire it acts as a electromagnet.
      • Electromagnets are used in electric bells, by doctors to remove magnetic material accidentally fallen in eye & to lift heavy loads.
      8. Electric Bell:
      • It works on the principle of magnetic effect of electric current.
      • It converts electrical energy to sound energy.
      • It consists of  coil of wire wound on an iron piece which acts like a electromagnet.
      • There is iron strip with a hammer at one end & other end near a contact screw.
      • When the iron strip touches the contact screw, the current flows through the coil which acts like a electromagnet pulls the iron strip.
      • Due to this pull the hammer at the end of the strip strikes the gong to produce the sound.
      • The pull also breaks the circuit & the current stops flowing through the circuit.