CBSE – 7th Standard Science

Chapter 14 – Electric Current and its Effects

Chapter 14

       Electric Current and its Effects

  • Some common electric components can be represented by symbols. some electric components and their symbols

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  • Switch in ‘OFF’  position    ____  ·               ·____
  • Switch in ‘ON’ position _____.·——– ·  ____
  • Wire _______
  • Electric cell —- ô। —-

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  • The positive terminal of one cell is connected to the negative terminal of the next cell.

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  • Such a combination of two or more cells is called a battery.
  • The wire gets hot when an electric current passes through it. This is the heating effect of the electric current.

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  • An electric room heater or an electric heater used for cooking contain a coil of wire.

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  • This coil of wire is called an element when these appliances are switched on requirements, become red hot and give out heat.
  • The amount of heat produced in a wire depends on its material, length and thickness.
  •  Thus, for different the wires of different materials and different lengths and thicknesses are used
  • An electric bulb is used for light but it also gives heat. In the bulb there is a thin wire, called the filament, which glows when an electric current passes through it.
  • When the bulb gets fused, its filament is broken.
  • Heating of bulb results in the wastage of electricity.
  • This wastage can be reduced by using fluorescent tube lights in place of the bulbs.
  • Compact fluorescent lamps (CFLs) also reduce wastage and can be fixed in the ordinary bulb holders.
  • Fuses of different kinds are used for different purposes.
  • Fuses are generally used in electrical appliances. the nichrome wire, a thin strand of steel wool are used for making electric fuses

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  • The needle of a compass is a tiny magnet, which points in north-south direction. When a magnet is bring close to it, the needle gets deflected.
  • Hans Christian Oersted  was the first person who noticed the deflection of compass needle every time the current was passed through the wire when electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current.
  •  In fact, an electric current can be used to make magnets. The coil behaves like a magnet when electric current flows through it, the electric current is switched off, the coil generally loses its magnetism. Such coils are called electromagnets.

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  • It is convenient to represent electric components by symbols. Using these, an electric circuit can be represented by a circuit diagram.
  • When an electric current flows through a wire, the wire gets heated. It is the heating effect of current. This effect has many applications.
  • Wires made from some special materials melt quickly and break when large electric currents are passed through them.
  • These materials are used for making electric fuses which prevent fires and damage to electric appliances.
  • When an electric current flows through a wire, it behaves like a magnet.

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  • A current carrying coil of an insulated wire wrapped around a piece of iron is called an electromagnet.
  • Electromagnets are used in many devices.
  • (The steel wool is commonly used for cleaning utensils and is available in grocery shops.) If there are any fans in the room, switch them off.
  • Now pass the current through the circuit for sometime.
  •  Wires made from some special materials melt quickly and break when large electric currents are passed through them.
  • In all buildings fuses are inserted in all electrical circuits.
  • There is a maximum limit on the current which can safely flow through a circuit.
  •  If by accident the current exceeds this safe limit, the wires may become overheated and may cause fire.
  •  If a proper fuse is there in the circuit, it will blow off and break the circuit.
  • A fuse is thus a safety device which prevents damages to electrical circuits and possible fires.
  • One reason for excessive currents in electrical circuits is the direct touching of wires.
  • This may happen if the insulation on the wires has come off due to wear and tear. This may cause a short circuit.
  •  Another reason for excessive current can be the connection of many devices to a single socket.
  • This may cause overload in the circuit.
  • You might have read reports in newspapers about fires caused by short circuits and overloads.
  • An electric bulb is used for light but it also gives heat.
  • This is not desirable. This results in the wastage of electricity.
  • This wastage can be reduced by using fluorescent tube lights in place of the bulbs.
  • Compact fluorescent lamps (CFLs) also reduce wastage and can be fixed in the ordinary bulb holders.
  • Tube lights and CFLs However, before buying bulbs or tubes, or CFLs, look for the ISI mark of the Bureau of Indian Standards. In fact, before buying any electrical appliance, look for this mark.
  •  The ISI mark ensures that the appliance is safe and wastage of energy is minimum.

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CBSE 7th Standard Science

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CBSE 7th Standard Science Syllabus and Revision Notes

  • Chapter 1 – Nutrients in plants
  • Chapter 2 – Nutrition in Animals
  • Chapter 3 – Fibre to Fabric
  • Chapter 4 – Heat
  • Chapter 5 – Acids bases and salts
  • Chapter 6 – Physical and Chemical Changes
  • Chapter 7 – Weather, Climate and Adaptations of Animals to Climate
  • Chapter 8 – Winds, Storms and Cyclone
  • Chapter 9 – Soil
  • Chapter 10 – Respiration in Organisms
  • Chapter 11 – Transportation in Animals and Plants
  • Chapter 12 – Reproduction in Plants
  • Chapter 13 – Motion and Time
  • Chapter 14 – Electric Current and its Effects
  • Chapter 15 – Light
  • Chapter 16 – Water: A Precious Resource
  • Chapter 17 – Forests: Our Lifeline
  • Chapter 18 – Waste water Story