Goa Board Class 6 Solutions for Science – Electricity and Circuits (English Medium)
Page No. 123:
Question 1:
Fill in the blanks:
(a) A device that is used to break an electric circuit is called ______ __.
(b) An electric cell has ______ __ terminals.
Solution:
(a) A device that is used to break an electric circuit is called __switch__.
Concept insight: A switch is an electric device that is used to break a circuit. When the switch is in ‘OFF’ position, then the circuit is not complete. Such a circuit is called an open circuit. An electric current cannot flow through this circuit.
(b) An electric cell has __two__ terminals.
Concept insight: An electric cell has two terminals, a negative terminal and a positive terminal (as shown in the given figure).
Question 2:
Mark ‘True’ or ‘False’ for the 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.
Solution:
(a) True
Concept insight: Metals are good conductors of electricity. Hence, an electric current can flow through metals.
(b) False
Concept insight: Jute string is a bad conductor of electricity so it cannot be used to make a circuit.
(c) False
Concept insight: Thermocol is a bad conductor of electricity. Hence, electric current cannot pass through it.
Question 3:
Explain why the bulb would not glow in the arrangement shown in figure.
Solution:
From the given figure, it can be observed that one terminal of the bulb is connected to a tester holder (it is made up of plastic). A current will not flow through the circuit. Hence the bulb would not glow.
Concept insight: Electric current cannot pass through objects such as plastic scale, tester holders, etc., because these objects are bad conductors of electricity.
Page No. 124:
Question 4:
Complete the drawing shown in fig. to indicate where the free ends of the two wires should be joined to make the bulb glow.
Solution:
The given circuit is not complete. To complete the circuit and make the bulb glow, the positive terminal of the cell should be connected to the free end of one of the wires from the switch (clip), and the base terminal of the bulb should be connected to the free end of the other wire from the switch. The closed circuit is shown in the following figure:
Concept insight: If a circuit is not complete, current will not flow through the circuit.
Question 5:
What is the purpose of using an electric switch? Name some electrical gadgets that have switches built into them.
Solution:
A switch is an electric device that is used to complete or to break an electric circuit. If the switch is ‘ON’, then a current can flow through the circuit. However, if the switch is ‘OFF’, then the current cannot flow through the circuit.
Electrical appliances such as table fans, electric lamps, washing machines, juicers and mixers, TV, radio, etc. have switches built into them.
Concept insight:Switch is device which regulates the functioning of a circuit by opening or closing a circuit.
Question 6:
Would the bulb glow after completing the circuit shown in the figure below if instead of safety pin we use an eraser?
Solution:
Erasers are bad conductors of electricity. They do not allow electric current to pass through them. The circuit becomes an open circuit. Hence, the bulb will not glow if the safety pin is replaced by an eraser.
Concept insight: Bad conductors of electricity do not conduct electricity. For example: plastics, eraser etc.
Question 7:
Would the bulb glow in the circuit shown in Fig?
Solution:
The bulb will not glow. This is because the two terminals of the cell are connected to the single terminal of the bulb. This is equivalent to the bulb not being connected in the circuit at all. The two terminals of the cell should be connected to the two terminals of the bulb.
Concept insight: Two terminals of the bulb should be connected to the two terminals of the cell, otherwise it will not glow.
Question 8:
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.
Solution:
When the two free ends of a conductor tester are touched with an object, then the bulb of the tester would glow if the object conducts electricity. However, the bulb would not glow if the object does not conduct electricity. Since the bulb glows when the tester is touched with the given object, the object must conduct electricity. Hence, the given object is a conductor.
Concept insight: A good conductor allows electricity to pass through it.
Question 9:
Why should an electrician use rubber gloves while repairing an electric switch at your home? Explain.
Solution:
An electric switch is an electrical appliance which conducts electricity through its internal parts. When its internal parts are touched with naked hands, then it may cause an electric shock. Therefore, it should be touched with rubber gloves in hands because rubber cannot conduct electricity. Hence, electricians should wear rubber gloves while repairing a switch or any other electrical appliance.
Concept insight: Rubber is a bad conductor of electricity so it protects the electrician from electric shock while repairing electrical switches.
Question 10:
The handles of the tools like screwdriver and pliers used by electricians for repair work usually have plastic or rubber covers on them. Can you explain why?
Solution:
Rubber and plastic are bad conductors of electricity. They do not allow electric current to flow through them. Hence, handles of tools such as screwdrivers, pliers, etc. which are used by electricians for repair work usually have plastic or rubber cover on them. This protects them from electric shocks.
Concept insight: Plastic and rubber are bad conductors of electricity.