# Chapter 12 Electricity and Circuits

• Electricity is the source of light.
• An electric cell is made up of two terminal: one is positive (+) and the other one is negative (-).
• The cell which converts chemical energy to electric energy is known as electric cell.
• An electric bulb glows due to the flow of electric current which produces electricity.
• An electric bulb is made up of two parts: a thin wire made up of filaments and a pair of thick wires called terminal.
• An electric bulb glows when it is connected to the electric cell.
• When the path of electricity is complete, known as electric circuit.
• The objects through which the electricity can pass easily called conductors.
• The objects through which electricity cannot pass called insulators.
• A device which is used to complete or break the electricity called switch.

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### Exercise 1 ( Page No. : 124 )

•  Q1 Fill in the blanks : (a) A device that is used to break an electric circuit is called _______________. (b) An electric cell has _______________ terminals. Ans: (i) Switch                                                                                                                                                                                                                                      Switch is the device which is used to break or continue the electric current.   (ii) Two                                                                                                                                                                                                                                                   An electric cell has two terminals: Positive or Negative. Q2 Mark 'True' or 'False' for following statements: (a) Electric current can flow through metals. (b) Instead of metal wires, a jute string can be used to make a circuit. (c) Electric current can pass through a sheet of thermo Col. Ans: (a) True Because metals are good conductor of electricity. (b) False It is false because jute is an insulator of electricity, so we cannot use this. (c) False This statement is false because thermocol is the insulator of electricity. Q3 Explain why the bulb would not glow in the arrangement shown in Fig. 12.13. Ans: The bulb would not glow in this arrangement because, the terminals of the bulb are connected to the insulator part (plastic) to the screw driver. Here the circuit is not complete. For the bulb to glow, there must be a conductor that will be connected to the electric cell. Q4 Complete the drawing shown in Fig 12.14 to indicate where the free ends of the two wires should be joined to make the bulb glow. Ans: Here, the free ends of the wires should be connected to the bulb to complete the circuit. Q5 What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them. Ans: Electric switch is a device which is used to break or to continue the electricity in electricity circuit. It is easy to handle electricity used easily with the help of an electric switch. Some electrical gadgets that have switch built into them are freeze, microwave, toasters etc. Q6 Would the bulb glow after completing the circuit shown in Fig. 12.14 if instead of safety pin we use an eraser? Ans: The objects through which electricity can pass easily are called conductors and other one from which electricity cannot pass through them are called insulators. For a bulb to glow, there should be presence of conductors. Here bulb is not glowing if we use an eraser at the place of pin because eraser is an insulator of electricity. So, here circuit is not complete, so the bulb will not glow. Q7 Would the bulb glow in the circuit shown in Fig. 12.15? Ans: The bulb would not glow in the circuit because here the electric circuit is not complete. For the bulb to glow, circuit must be complete so that electric current pass through it. A glowing bulb shows that there current is flowing from the positive terminal of the battery to the negative terminal. Diagram: Q8 Using the "conduction tester" on an object it was found that the bulb begins to glow. Is that object a conductor or an insulator? Explain. Ans: Using, the “conductor tester” on an object. It was found that the bulb begins to glow, then it must be conductor. Conductors are those from which electricity can pass through easily. To complete an electric circuit, a battery should be connected to the conductor material. So, here the bulb begins to glow. Q9 Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain. Ans: An electrician use rubber gloves while repairing an electric switch at home because rubber is the insulator of electricity. It protects the electrician from the electric shock. So the electrician use rubber gloves. Q10 The handles of the tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them. Can you explain why? Ans: The handles of the tools like screw driver and pliers used by electrician for the repairing usually contains plastic or rubber covers on them because plastic or rubber both are the insulators of the electricity. Covering of the plastic or rubber on the tools helps the electrician to repair easily because using covered tools protect them from an electric shock.