Question 1. Complete the following sentence.
(a) _______, _______ and _______ are the liquids that conduct electricity.
(b) _______ is the effect generated when an electric current is passed through a solution.
(c)_______ is known as the process for depositing a layer of any metal on another material by the means of Electricity.
(a)Acids, Bases and Salts.
Question 2. Explain; Why a magnetic needle shows deflection, when the free end of a tester are dipped into a solution?
Solution : The compass needle shows a deflection which concludes that current is flowing through the wire. The circuit becomes complete as the free ends of the tester are immersed inside the solution. So, the solution is conducting solution and that is the reason why a deflection is obtained in the compass needle.
Question 3. Name three liquids which may cause a deflection in the magnetic needle when tested in a manner shown below.
Solution : It may be the salt solution in water.
Question 4. The bulb does not glow in the setup shown in fig. 14.1. List the possible reasons. Explain your answer.
Solution : The possible reasons are:
(i) The solution may be conducting electricity but the current produced it too small, so that the filament of the bulb does not get heated and the bulb does not glow.
(ii) It is possible that the connections are loose.
(iii) The cells are used up.
Question 5. A tester is used to check the conduction of electricity through two liquids. Labelled A and B. it is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. you would conclude that
(i) Liquid A is a better conductor than liquid B
(ii) Liquid B is a better conductor than liquid A
(iii) Both liquids are equally conducting
(iv) Conducting properties of liquid cannot be compared in this manner.
Solution : (i) Liquid A is a better conductor than liquid B.
Question 6. Does pure water conduct electricity? If not, what can we do to make it conducting?
Solution : Pure water does not conduct electricity because there are no salts dissolved in it. Therefore, it is a poor conductor of electricity. To make it conducting, we can add impurities like common salt, lemon juice, vinegar, etc.
Question 7. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.
Solution : Water usually contains impurities which makes it a good conductor of electricity. If the electrical supply is not shut off, then electricity may pass through water and harm the firemen. This is the reason in case of a fire, before the firemen use the water hoses; they shut off the main electrical supply for the area.
Question 8. A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Solution : The amount of salts dissolved in the sea water is more than the drinking water. The drinking water is normally treated and purified which removes impurities present in it. Therefore, the compass needle deflects more in the case of sea water.
Question 9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Solution : No, it is not safe for the electrician to carry out electrical repairs outdoors during heavy downpour because the rain water contains dissolved salts. This makes rain water a good conductor of electricity; hence, it might cause electrical shock to electrician.
Question 10. Paheli had heard that rain water is as good as distilled water. So, she collected some rain water in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle showed deflection. What could be the reasons?
Solution : Rain water contains dissolved salts. This makes it a conducting solution. There are no dissolved salts present in the distilled water. Hence, rain water can allow electricity to pass through it while distilled water cannot.
Question 11. Prepare a list of objects around you that are electroplated.
Solution : Examples of electroplated objects are as follows:
(i) Chromium plating is done on different parts of cars, buses and motor cycles to give them shiny appearance.
(ii) A fine layer of gold is deposited on the silver ornaments and they are called gold-plated ornaments.
(ii) Iron used in constructing a building is coated with a layer of zinc. This protects iron from corrosion and rusting.
Question 12. The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Solution : Copper ion is positively charged. It is attracted towards the plate which is connected to the negative terminal of the battery. As copper ions are transferred to the thin copper plate, this thin pure copper plate must be connected to the negative terminal of the battery. Consequently, impure copper rod is connected to the positive term of the battery.