Question 1When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason.
The deflection in the compass needle shows that current in flowing through the circuit. The circuit is complete since free ends of the tester are dipped in a solution. The solution is certainly a conducting solution.This is the reason why the compass needle shows a deflection.
Question 4A 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
If the bulb does not glow at all with liquid A and glows very dimly with liquid B. It means that liquid B is a better conductor of electricity. So answer will be (i).
Question 6In 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.
The water used in water hoses is not pure water and it conducts electricity. Fire shut off the main electrical supply for area because if the supply of electricity continues these may be high risk of electrocution is whole the area due to water.
Question 7A 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?
Seawater contains higher amounts of salts in compare to drinking water hence sea water is a better conductor of heat. This is the reason that the compass needle deflects more in case of sea water.
Question 9Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater 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?
Though rainwater is as pure as distilled water yet it may be contaminated by the impurities suspended in the atmosphere. These impurities make the rainwater conducting. This could be the reason for the deflection of compass.
Question 11In the process of 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 battery and why?
To perform such activity copper sulphate crystals and two copperplates each of the size around 10 cm long and 4 cm wide are required. Now take 250 mL of distilled water in a clean and dry beaker. Dissolve two teaspoonfuls of copper sulphate crystals in it to obtain copper sulphate solution. (You may add a drop of dilute sulphuric acid to copper sulphate solution to make it more conducting). Clean each copper plate with sand paper. Now rinse it with water and dry it. With the help of wires, connect one copper plate to each terminal of a two cell battery (Take care that the two plates do not touch each other). Immerse the two plates in copper sulphate solution allow the current to pass through for 5-7 minute.
When electric current is passed through the copper sulphate solution, copper sulphate disassociates into copper and sulphate. The free copper gets drawn to the plate connected to the negative terminal of the battery and thus gets deposited on that plate. Gradually a layer of copper builds up on the plate.