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__. (The solutions of acids, bases or salts are
conducting in nature. They allow the current to pass through.)
(b) The passage of an electric current through a solution
causes chemical__effects. (When an electric current
passes through a solution, the solution decomposes into its positive and
negative ions. This process of decomposition of the solution is a chemical
effect.)
(c) If you pass current through copper sulphate solution,
copper gets deposited on the plate connected to the negative
terminal of the battery. (When an electric current passes through a copper
sulphate solution, the solution decomposes into positively charged copper ions
and negatively charged sulphate ions. These positively charged copper ions get
attracted towards the plate which is connected to the negative terminal of a
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 in the
compass needle shows that current is flowing through the wounded wire and
hence, 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 3: Name
three liquids, which when tested in the manner shown in Fig. 14.9, may cause
the magnetic needle to deflect.
Answer: Liquids like lemon
juice, salt water and vegetable oil allow electricity to pass through them.
Hence, these liquids can be used as in the beaker to show the given effect.
Question 4: The
bulb does not glow in the setup shown in Fig.
Answer: The bulb may not glow
because of the following reasons:
(i) Liquid in the beaker is non-conducting. In such case,
the electric current would not be able to pass through the liquid. Hence, the
circuit is not complete.
(ii) Electric current in the circuit is very weak. This can
happen if the material used for making the circuit is not a good conductor of
electricity or the battery does not have sufficient energy to generate
electricity.
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.
Answer:
(i) Liquid A is a better conductor than liquid B. The amount
of current flowing through a conducting solution depends on the conductivity of
the solution. With more conductivity, more current passes through the solution
and vice-versa. Hence, the conductivity of liquid A is more than the
conductivity of liquid B.
Question 6: Does
pure water conduct electricity? If not, what can we do to make it conducting?
Answer: No. Pure water does not
conduct electricity. This is because pure water is devoid of any salts. Pure
water can conduct electricity when a pinch of common salt is added to it, as
salt solution is conducting in nature.
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 may conduct
electricity. If the electrical supply for the area is not shut off and water is
poured over electrical appliances, then electricity may pass through water and
harm the firemen. That is why, in case of a fire, the firemen shut off the main
electrical supply for the area before they use the water hoses.
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?
Answer: Sea water contains more
dissolved salts than the drinking water. Hence, it is more conducting than the
drinking water. Because of this reason, the compass needle deflects more in
seawater than in the drinking water.
Question 9: Is
it safe for the electrician to carry out electrical repairs outdoors during
heavy downpour? Explain.
Answer: No. It is not safe to
repair electrical appliances outdoors during heavy downpour. This is because
rain water contains dissolved salts. Therefore, rain water can conduct
electricity. The electrician may get electrical shocks while working outdoors
during rain.
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?
Answer: 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.
Answer: 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.
iii. 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?
Answer: 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
terminal of the battery.
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