Science Ncert_exemplar 2019 Solutions for Class 8 Science Chapter 14 Chemical Effects Of Electric Current are provided here with simple step-by-step explanations. These solutions for Chemical Effects Of Electric Current are extremely popular among Class 8 students for Science Chemical Effects Of Electric Current Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science Ncert_exemplar 2019 Book of Class 8 Science Chapter 14 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science Ncert_exemplar 2019 Solutions. All Science Ncert_exemplar 2019 Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

Page No 77:

Question 1:

An electric current can produce
(a) heating effect only.
(b) chemical effect only.
(c) magnetic effect only.
(d) chemical, heating, and magnetic effects.

Answer:

An electric current can produce:

  • chemical effect (electroplating)
  • heating effect (electric heater)
  • magnetic effects (door bell)
Hence, the correct answer is option (d).

Page No 77:

Question 2:

Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in the given figure.
figure 
They found that the bulb in the setup A glows more brightly as compared to that of the setup B. You would conclude that
(a) higher current is flowing through the circuit in setup A.
(b) higher current is flowing through the circuit in setup B.
(c) equal current is flowing through both the circuits.
(d) the current flowing through the circuits in the two setups cannot be compared in this manner.

Answer:

Higher current is flowing through the circuit in setup A. As the bulb in the circuit A glows more than that of B, it means the solution in circuit A, conducts more electricity as compared to the solution in circuit B.
Hence, the correct answer is option (a).



Page No 78:

Question 3:

Boojho’s uncle has set up an electroplating factory near his village. He should dispose off the waste of the factory
(a) in the nearby river.
(b) in the nearby pond.
(c) in the nearby cornfield.
(d) according to the disposal guidelines of the local authority.

Answer:

Electroplating factory waste contains harmful chemicals. So, one should dispose off the waste of the factory according to the disposal guidelines of the local authority.
Hence, the correct answer is option (d).

Page No 78:

Question 4:

When electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates
(a) the chemical effect of current.
(b) the heating effect of current.
(c) the magnetic effect of current.
(d) the lightning effect of current.

Answer:

Changing of colour of the solution on passing electricity indicates the chemical change occur in the solution due to chemical effect of current.
Hence, the correct answer is option (a).

Page No 78:

Question 5:

Which one of the following solutions will not conduct electricity?
(a) lemon juice          (c) tap water
(b) vinegar                (d) vegetable oil

Answer:

Vegetable oil does not conduct electricity.
Hence, the correct answer is option (d).

Page No 78:

Question 6:

Which of the following metals is used in electroplating to make objects appear shining?
(a) iron             (c) chromium
(b) copper        (d) aluminium

Answer:

Chromium is a shining metal, so, the chromium is used in electroplating over other metals to make them shine.
Hence, the correct answer is option (c). 

Page No 78:

Question 7:

figure
Which of the following solutions will not make the bulb in the given figure glow?
(a) sodium chlorides
(b) copper sulphate
(c) silver nitrate
(d) sugar solution in diluted water

Answer:

Sugar solution in distilled water does not show any chemical change, so it will not conduct electricity. Hence, it will not cause the bulb glow. While the other solutions (sodium chlorides, copper sulphate and silver nitrate) will conduct electricity and make the bulb glow.
Hence, the correct answer is option (d).



Page No 79:

Question 8:

Fill in the blanks
(a) The object to be electroplated is taken as ____________ electrode.
(b) One of the most common applications of chemical effect of electric current is ______________.
(c) Small amount of a mineral salt present naturally in water makes it a______________ of electricity.
(d) Electroplating of ______________ is done on objects like water taps and cycle bell to give them a shiny appearance.

Answer:

(a) cathode
(b) electroplating
(c) conductor
(d) chromium










 

Page No 79:

Question 9:

Why is a layer of zinc coated over iron?

Answer:

Electroplating of zinc over iron is done to protect it from rusting. Zinc coated over iron detach it from air and moisture of the surrounding and hence protect iron from rusting.

Page No 79:

Question 10:

Will the solution of sugar in distilled water conduct electricity?

Answer:

No, the solution of sugar in distilled water will not conduct electricity. Sugar solution does not break in ions on passing electricity through it and hence, it does not conduct electricity.

Page No 79:

Question 11:

Name the effect of current responsible for the glow of the bulb in an electric circuit.

Answer:

The glowing of bulb in an electric circuit is due to heating effect of electric current. The filament of the bulb gets heated and glows on passing electricity through it.

Page No 79:

Question 12:

Boojho made the circuit given in the figure and observed that the bulb did not glow. On Paheli’s suggestion he added one more cell in the circuit. The bulb now glows. Explain.
figure

Answer:

One cell was not able to provide sufficient voltage to cause the current to glow the bulb initially. When one more cell is added to the circuit, the voltage across the circuit increases, and it starts providing sufficient current to glow the bulb. 



Page No 80:

Question 13:

Paheli set up an experiment using liquid A in the beaker as shown in the given figure. She observed that the bulb glows. Then she replaced the liquid A by another liquid B. This time the bulb did not glow. Boojho suggested replacing the bulb by an LED. They observed that the LED glows. Explain.

Answer:

The experiment suggests that the liquid B conducts less current as compared to liquid A and LED ( light emitting diode) requires less current to glow. So, the LED glows, even in the circuit with liquid B.

Page No 80:

Question 14:

Paheli wants to deposit silver on an iron spoon. She took silver nitrate (AgNO3) solution in a beaker and setup a simple circuit for electroplating. Which terminal of the battery should the spoon be connected to? What material should the other electrode be made of?

Answer:

The spoon should be connected to the negative terminal of the battery. The other electrode connected to the positive terminal, should be made of silver. Silver nitrate is used as a solution. When electric current is passed, silver nitrate breaks into silver and nitrate ions, and the silver ions ( positive ion) get attracted to the negative plate and get deposited on the spoon.



Page No 81:

Question 15:

Why is tin electroplated on iron to make cans used for storing food?

Answer:

Iron is a reactive metal and gets rusted, when comes in contact of air and moisture. Tin is relatively less reactive than iron. Tin coating prevents food from coming in contact with iron and thus prevents it from getting spoiled.

Page No 81:

Question 16:

Observe the given figure.
figure
Which of these two circuits A or B shows the correct observation?

Answer:

Circuit A will shows the correct observation.

Page No 81:

Question 17:

Observe the following circuits carefully. In which circuit will the bulb glow. Write ‘Yes’ or ‘No’ in the blank space provided along each of the circuit given in the given figure.
figure

Answer:

Coal and eraser do not conduct electricity while iron nail and steel spoon conduct electricity. So, the bulb in the circuit with iron nail and steel spoon will glow. 
Hence, the correct answer is below:




 



Page No 82:

Question 18:

An electric current is passed through a conducting solution. List any three possible observations.

Answer:

When an electric current passes through a conducting solution, the following changes may observe:

  • Change in the colour of the solution.
  • The solution may get heated.
  • Deposits of metal may be seen on electrodes.

Page No 82:

Question 19:

In the circuit in the given figure, Boojho observed that copper is deposited on the electrode connected to the negative terminal of the battery. Paheli tried to repeat the same experiment. But she could find only one copper plate. Therefore she took a carbon rod as negative electrode. Will copper be still deposited on the carbon rod? Explain your answer.
figure

Answer:

Yes, copper from the copper sulphate solution will be deposited on the carbon rod. Carbon rod act as a negative plate and positive copper ions released in the solution will still get attracted to the carbon rod and will be deposited on it.



Page No 83:

Question 20:

Observe the circuit given in figure.
figure
Boojho set up this circuit for purification of copper. What will be the nature of – (i) plate A (ii) plate B (iii) the solution.
Explain the process of purification.
 

Answer:

For the purification of copper, the following arrangement should be done:
(i) Plate A: pure copper 
(ii) Plate B: impure copper
(iii) the solution: copper sulphate solution
Copper from impure copper plate is transferred to the pure copper plate by the process of electroplating.
 



Page No 84:

Question 21:

Observe the following circuit given in Figure.
figure
Current does not flow in the circuit if there is a gap between the two wires. Does it indicate that air is a poor conductor of electricity? Does air never conduct electricity? Explain.

Answer:

Yes, if current is not flowing through the air gap between the wires, it means that air is a poor conductor of electricity. But moist air can conduct electricity. So, under certain conditions, such as during lightning, air may conduct electricity.

Page No 84:

Question 22:

Boojho made the circuit shown in the given figure. He wanted to observe what happens when an electric current is passed through water. But he forgot to add a few drops of lemon juice to water. Will it make any difference to his observations? Explain.
figure

Answer:

Distilled or pure water does not conduct electricity in normal condition due to scarcity of formation of ions. So, If the water is distilled water and lemon juice is not added, no current will pass through the circuit. But if the water taken is salty, then a feeble current will pass through the circuit and bubbles will be seen on the negative electrode. 
On adding few drops of lemon juice in water, the conductivity of the water increases due to formation of ions.



Page No 85:

Question 23:

Observing that the bulb does not glow in the circuit shown in the given figure A, Boojho changed the circuit as shown in the given figure B. He observed deflection in the magnetic compass.
(i) What does the deflection in magnetic compass indicate?
(ii) Why did the bulb not glow in the given figure A?
(iii) What would be the effect of increase in the number of turns in the coil wound around the magnetic compass in the given figure?
(iv) What will be observed if the number of cells are increased in the circuit shown in the given figure B?

Answer:

(i) Deflection in magnetic compass needle indicates that, there is current passing through the circuit. Due to magnetic effect of current, it applies force on the magnetic needle of compass and hence deflection occurs.
(ii) The bulb in the figure A does not glow as the current in the circuit is insufficient to make it glow.
(iii) If number of turns in the coil increases, more magnetic force will start acting on the compass needle and hence, more deflection in compass needle will occur.
(iv) Adding more cells, results in more current through the circuit and hence more deflection in compass needle.
 

Page No 85:

Question 24:

You are provided with a magnetic compass, an empty match box, a battery of two cells and connecting wires. Using these objects how will you make a tester for testing an electric circuit? Draw the necessary circuit diagram and explain.

Answer:

We should  first put the compass in the match box. Then wound the wire on the box making spiral coils on it. Attach two ends of the wire  with the two terminals of the cell. Whenever the current passes through the coil, magnetic field generates and hence the magnetic force acts on the magnetic needle of the compass. As a result, it deflects.
The circuit diagram is as below:



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