Exercises
Question 1
Fill in the blanks.
(a) Most liquids that conduct electricity are solutions of ..............., ............... and ...............
(b) The passage of an electric current through a solution causes ............... effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ............... terminal of the battery.
(d) The process of depositing a layer of any desired metal on another material by means of electricity is called ...............
Answer
(a) Most liquids that conduct electricity are solutions of acids, bases and salts.
(b) The passage of an electric current through a solution causes chemical effects
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.
(d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
Question 2
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Answer
The deflection of the magnetic needle can be explained by the flow of current through the wounded wire of the tester. When the free ends of a tester are dipped into a solution, the circuit becomes complete and current starts flowing through the solution proving that the solution is a good conductor of electricity. The current then flows through the wire creating a magnetic field that deflects the magnetic needle.
Question 3
Name three liquids, which when tested in the manner shown in Fig.11.9, may cause the magnetic needle to deflect.
Answer
- Saltwater
- Lemon juice
- Vinegar
Question 4
The bulb does not glow in the setup shown in Fig.11.10. List the possible reasons. Explain your answer.
Answer
Potential reasons for the bulb not glowing include:
- The bulb might be defective or fused or the battery might be dead.
- If the bulb and battery are replaced and the bulb still fails to light up, it suggests there could be issues with the connectivity, such as loose or faulty connections.
- If after checking and fixing the connections, the bulb still doesn't glow, it means that the solution in the setup doesn't let electricity pass through.
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
- liquid A is a better conductor than liquid B.
- liquid B is a better conductor than liquid A.
- both liquids are equally conducting.
- conducting properties of liquid cannot be compared in this manner.
Answer
Liquid A is a better conductor than liquid B.
Reason — The brightness of the bulb is determined by the current through the circuit, which in turn depends on the conductivity of the solution. The greater the conductivity, the greater will be the quantity of current passing through the solution and as a result the bulb will glow brightly. Hence, liquid A is a better conductor than liquid B as the bulb glows more brightly in liquid A.
Question 6
Does pure water conduct electricity? If not, what can we do to make it conduct?
Answer
Distilled or pure water is free from salts and is a bad conductor of electricity.
When common salt (Sodium Chloride, i.e., NaCl) is dissolved in water, it becomes a good conductor.
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.
Answer
Water from hoses contain salts which makes the water conducting and when that conducting water is sprayed in order to stop the fire, it might result in spread of electric current if water is spilled over electrical switches. Hence, firemen shut off the main electrical supply for the area under fire.
Question 8
A child staying in a coastal region tests the drinking water and also seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Answer
The amount of salts dissolved in seawater is more than that in drinking water. So, seawater will be a better conductor than drinking water. Hence, sea water shows increased deflection of the needle as compared to the drinking water.
Question 9
Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpours? Explain.
Answer
It is unsafe for an electrician to conduct electrical repairs outdoors during heavy downpours. Rainwater, containing dissolved salts, serves as a good conductor of electricity. If it comes into contact with electrical components or wiring, it can establish a path for the electric current, posing a risk of electric shock to the electrician.
Question 10
Paheli 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?
Answer
The deflection of the compass needle in Paheli's rainwater sample could be due to the presence of dissolved ions or impurities in the rainwater. While rainwater is generally considered relatively pure, it can still pick up impurities from the atmosphere, such as dust, gases, or salts. These salts can make the rainwater conductive to some extent causing it to conduct electricity slightly and affect the behavior of the compass needle.
Question 11
Prepare a list of objects around you that are electroplated.
Answer
Some of the common objects around us that are electroplated are:
- Car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims are electroplated with chromium as it has a shiny appearance.
- Ornaments are electroplated with gold or silver.
- Tin cans, used for storing food, are made by electroplating tin onto iron.
- Bridges and automobiles are made of iron, which can rust easily. Hence, they are electroplated with zinc to protect it from corrosion and rust.
Question 12
The process that you saw in Activity 11.7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the 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?
Answer
The thick rod of impure copper should be attached to the positive terminal of the battery in the purification process of copper. This is because, during the passage of electric current through copper sulphate solution, it breaks down into copper and sulphate ions. The positively charged copper ions are attracted to the negative terminal of the battery, where they get deposited on the thin plate of pure copper. Simultaneously, the impure copper rod, linked to the positive terminal, contributes copper ions to compensate for the loss in the solution. This ensures the overall purification of copper during the process.