Topic outline

    • Electric Current and its Effects

      Q18. We could not see element in electrical appliances. Give reason.

      Ans. We could not see element in electrical appliances because electrical appliances, such as immersion heaters, hotplates, irons, geysers, electric kettles, hair dryers, have elements inside them.


      Q19. Why a fused bulb does not glow?

      Ans. A break in the filament of an electric bulb means a break in the path of the current between the terminals of the electric cell. Therefore, a fused bulb will not glow as current does not passes through its filament.


      Q20. Sometimes the cells are placed side by side. Then how are the terminals of the cells connected?

      Ans. There is usually a thick wire or a metal strip connecting the positive terminal of one cell to the negative terminal of the next cell.

      Q21. Why should we look for ISI mark on electrical appliances?

      Ans. Before buying any electrical appliance we should look for ISI mark because this mark ensures that the appliance is safe and wastage of energy is the minimum.


      Q22. On what factors does the heat produced in a wire depend?

      Ans. The amount of heat produced in a wire depends on its material, length and thickness. Thus, for different requirements, the wires of different materials and different lengths and thicknesses are used.


      Q23. What is battery? How can it be made using cells?

      Ans. A combination of two or more cells is called a battery. Battery can be made by connecting two or more cells together. The positive terminal of one cell is connected to the negative terminal of the next cell.


      Q24. What are electromagnets?

      Ans. A core of magnetic material (such as iron) surrounded by a coil of wire behaves like a magnet when electric current flows through it. When the electric current is switched off, the coil generally loses its magnetism. Such coils are called electromagnets.

      Q25. How does a heating element work in an electric heater?

      Ans. An electric room heater or an electric heater used for cooking. All these contain a coil of wire. This coil of wire is called an element. When these appliances are switched on after connecting to the electric supply, their elements become red hot and give out heat.


      Q26. Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

      Ans. No, an electromagnet cannot be used for separating plastic bags from a garbage heap because plastic bag is a non-magnetic material and will not be attracted by an electromagnet.


      Q27. What is MCB and what is it used for?

      Ans. These days Miniature circuit breakers (MCBs) are increasingly being used in place of fuses. These are switches which automatically turn off when current in a circuit exceeds the safe limit. We can turn them on and the circuit is once again complete.


      Q28. An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

      Ans. No, electrician should not replace a fuse by a piece of wire because for fuse, wires made from some special materials are used so that it melt quickly and break when large electric currents passes through them.

      Q29. What are the reasons for excessive currents in the electrical circuits?

      Ans. 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.


      Q30. The following Fig. shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.

      Image from NCERT



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