G.Science

• Electric circuit components and their symbols

  • Electric cell
  • Electric bulb
  • Switch in 'ON' position
  • Switch in 'OFF' position
  • Battery
  • Wire
• Switch symbol

  'ON' position and 'OFF' position represented by symbols
• Electric cells are connected in series to make a battery
• Paheli and Boojho had set up an electric circuit game as suggested in Class VI
• Electric cell symbol

  Longer line represents positive terminal, thicker shorter line represents negative terminal
• Many devices like torches, transistors, toys, TV remote controls use batteries
• Heating effect of electric current: Wires get hot when current passes through them
• Electric current passes through a wire, causing the filament of a bulb to glow
• Incandescent electric bulbs give off heat in addition to light, resulting in electricity wastage
• LED bulbs are more electricity efficient compared to incandescent bulbs or fluorescent tubes
• Fuses are inserted in electrical circuits to prevent excessive currents
• Excessive currents in electrical circuits can be caused by short circuits or overloads
• Miniature circuit breakers (MCBs) are increasingly being used in place of fuses
• Wires are used for making electric fuses
• CAUTION: 'Never try to investigate an electric fuse connected to mains circuit on your own. You may, however, visit an electric repair shop and compare the burnt out fuses with the new ones'
• Materials that melt quickly and break when large electric currents are passed through them

  • Wires
• If a proper fuse is there in the circuit, it will blow off and break the circuit, preventing damages to electrical circuits and possible fires
• Types of fuses

  • Fuses used in buildings
  • Fuses used in electrical appliances
• Effect of current on a compass needle

  Connect wire to electric cell through a switch, observe compass needle direction, bring bar magnet near needle, move switch to 'ON' position
• Activity: Making an electromagnet

  Take insulated wire, wind it around an iron nail, connect wire ends to cell terminals through a switch, place pins on/near nail, switch on current, observe pins clinging to nail, switch off current
• CAUTION: 'Always use proper fuses specified for particular applications, carrying ISI mark. Never use just any wire or strip of metal in place of a fuse'
• An electric current can be used to make magnets
• When electric current passes through a wire

  It behaves like a magnet
• When current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position
• An electric bell has an electromagnet in it