Electricity and Circuits
Fill up the blanks:
(a) A device that is used to break an electric circuit is called _______.
(b) An electric cell has _______ terminals.
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 thermocol.
Explain why the bulb does not light up in the arrangement shown in Fig. 12.5.
The bulb does not light up in the arrangement because the circuit is not complete.
Complete the drawing shown in Fig. 12.6 to indicate where the free ends of the two wires should be joined to make the bulb glow.
What is the purpose of using an electric switch ? Name some electrical gadgets that have switches built into them.
Electric switches are used to stop or start the flow of current. Electric gadgets having switches built into them are heaters, geysers, televisions, mixi, electric bells, fan, cooler, air conditioners, microwave ovens etc.
Would the bulb glow after completing the circuit shown in Fig. 12.8 if instead of safety pin we use an eraser ?
Yes, the bulb will light up after completing the circuit. No, the bulb will not glow if we use eraser instead of safety pins.
Would the bulb glow in circuit shown in figure:
No, the bulb will not light up because woollen thread is an insulator and hence current will not flow through it.
Using your “conduction tester” on an object makes the bulb light up. Is the material of that object a conductor or an insulator? Explain.
The material of that object is a conductor as the bulb light up. It means that circuit is complete.
Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.
Yes, the electrician should use rubber gloves while carrying out electrical repairs because rubber is an insulator. So the electrician will not get electric shocks due to leakage of electricity.
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 ?
Wood or plastic are insulators and does not allow electricity to pass through it. Hence electricians must use screwdrivers, with wooden or plastic handles, when they carry out repairs to avoid electric shocks.
Will the torch bulb light up in following arrangement?
The inside of a torch looks like this.
When we close the switch, the circuit is completed and the bulb lights up. Draw a red line on the figure indicating the complete circuit ?
InText Questions and Answers
Take a torch that works on two electric cells. Open it and take out the electric cells. Insert them again in different arrangements and press the switch. Does the bulb light up each time ?
No, the bulb does not light up each time.
Collect several kinds of materials to test, such as coins, cork, rubber, glass, keys, pins, plastic scale, wooden block, pencil lead, aluminium foil, candle, sewing needle, thermocol, mica, pencil lead. Touch the free ends of the bare wires of conduction tester to each sample (Fig. 12.4) Make sure that the two wires do not touch each other.
Does the bulb always light up ? Make a table similar to Table, in your notebook and record your observations.