NCERT Exemplar Solution Class 8 Science Chapter 14
NCERT Exemplar Solution Class 8 Science Chapter 14 Chemical Effects of Electric Current all Questions Answer Solution. NCERT Exemplar Class 8 Science Chapter 14 Solution PDF.
NCERT Exemplar Solution Class 8 Science Chapter 14: Overview
NCERT Exemplar Solution Class 8 Science Chapter 14 |
|
Board |
NCERT |
Topic |
Exemplar Problem Solution |
Class |
8 |
Subject |
Science |
Chapter |
14 |
Chapter Name |
Chemical Effects of Electric Current |
NCERT Exemplar Solution Class 8 Science Chapter 14 Chemical Effects of Electric Current
Multiple Choice Questions
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:- d) Chemical, heating and magnetic effects.
When an electric current flows from the circuit it can produces chemical effect, magnetic effect and heating effect all.
2) Boojho and paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in fig. 14.1.
They found that the bulb in the set up A glows more brightly as compared to that of the set up B. You would conclude that
Boojho’s paheli’s
Experiment experiment
Fig. 14.1
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:- a) higher current is flowing through the circuit in setup A.
The bulb in circuit A was glowing more brightly than bulb B these occurs when the current is higher in that circuit.
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:- d) According to the disposal guidelines of the local authority.
Any type of metallic waste are harmful to the environment so these should be disposed as per the guidelines of local authority.
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 lighting effect of current.
Answer:- a) The chemical effect of current.
The change in colour of the solution is due to chemical reactions occurs in the solution these is the chemical effect of current.
5) Which one of the following solutions will not conduct electricity?
a) Lemon juice
b) Vinegar
c) Tap water
d) Vegetable oil
Answer:- d) Vegetable oil
Mostly the current conducting solutions are acids, bases or salts. Vegetable oil does not contain any salt . Therefore condition cannot be occur through it.
6) Which of the following metals is used in electroplating to make objects appear shining?
a) Iron
b) Copper
c) Chromium
d) Aluminium
Answer:- c) Chromium.
Chromium is shiny in appearance. Therefore it is used for electroplating objects to make shining. Other metals does not have shiny appearance.
7)
Fig. 14.2
Which of the following solutions will not make the bulb in fig. 14. 2 glow?
a) Sodium chlorides
b) Copper sulphate
c) Silver nitrate
d) Sugar solution in diluted water
Answer:- d) Sugar solution in diluted water.
Sugar solution and diluted water both cannot conduct the current. As they do not contain salt in it.
Very Short Answer Questions
8) Fill in the blanks
a) The object to be electroplated is taken as __________ electrode.
Answer:- The object to he electroplated is taken as cathode electrode.
b) One of the most common applications of chemical effect of electric current is ________.
Answer:- One of the most common applications of chemical effect of Electric Current is Electroplating.
c) Small amount of a mineral salt present naturally in water makes it a ___________ of electricity.
Answer:- Small amount of a mineral salt present naturally in water makes it a Conductor of electricity.
d) Electroplating of ____________ is done on objects like water taps and cycle bell to give them a shiny appearance.
Answer:- Electroplating of Chromium is done on objects like water taps and cycle bell to give them a shiny appearance.
9) Why is a layer of zinc coated over iron?
Answer:- Iron get rusted due to corrosion when it comes in contact with moist air . Zinc coating protects the iron from rusting and corrosion.
10) Will the solution of sugar in distilled water conduct electricity?
Answer:- No.The solution of sugar in distilled water cannot conduct electricity. Liquids which conduct electricity are mostly the solutions of acids, bases and salts. But sugar added in distilled water cannot conduct electricity, as distilled water is does not contain any salts in it and it is poor conductor of Electricity.
11) Name the effect of current responsible for the glow of the bulb in an electric circuit.
Answer:- The bulb glows due to the heating effect of Electric current. When the Electric current passes through it, the filament of the bulb get heated and reaches to the high temperature and it starts glowing.
Short Answer Questions
12) Boojho made the circuit given in fig. 14.3 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.
Fig. 14.3
Answer:- When first time boojho made circuit the amount of current will not be sufficient to glow the bulb. Therefore on addition of one more cell circuit gets the sufficient current and bulb glows.
13) Paheli set up an experiment using liquid A in the beaker as shown in fig. 14.4. 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.
Fig. 14.4
Answer:- The light was glow in the liquid A but did not glow in liquid B. These is because The current conducted through Liquid B may be weaker as compared to A. But when the bulb was changed with the LED, then that LED glows in liquid B. As liquid B was strong enough for glowing the LED. As LED needs less current to glow.
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:- For the deposition of the silver over the iron spoon paheli should take another electrode made up of silver. And negative terminal of the battery should be connected with iron spoon. So that the silver from silver nitrate will get deposited over the iron spoon and silver from silver electrode will dissolve in the silver nitrate.
15) Why is tin electroplated on iron to make cans used for storing food?
Answer:- Food can be get spoiled if comes in contact with the iron directly. Therefore tin coating is done over the iron, as tin is very less reactive as compared to iron. Thus tin cans are used for the storage of food.
16) Observe fig. 14.5
A B
Fig. 14.5
Which of these two circuits A or B shows the correct observation?
Answer:-
Here, figure A shows the correct circuit diagram / observation.
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 fig. 14.6.
answer :- No.
Bulb will not glow .
Answer :- yes. Bulb will glow.
Answer:- No. Bulb will not glow.
Answer:- yes. Bulb will glow.
Long Answer Questions
18) An electric current is passed through a conducting solution. List any three possible observations.
Answer:-
When an electric current is passed through the solution then an chemical reaction occurs in it.
On the electrodes, bubbles of gas may be appear.
On the electrodes, deposition of the metals can be seen .
There may be changes of colour in the solution.
19) In the circuit given as fig. 14.7 Boojho observed that copper is depositing 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.
PIC
Answer:- Electroplating is the process in which the deposition of the layer of the desired metal over Another metal/ material takes place with the help of electricity . In given condition, copper will be deposited over the carbon rod from the copper sulphate solution. And the copper of the copper plate will be dissolved in the solution of copper sulphate for electroplating. These means that copper is transferred from one electrode to the another electrode.
20) Observe the circuit given in fig. 14.8.
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.
A B
Fig. 14. 8
Answer:-
For performing these purification process, the nature of the plate A will pure copper, plate B – impure copper, and solution should be taken of copper sulphate.
Now as shown in figure, arrange the circuit and allow the current to pass for 15 min. When the Electric current passes from the solution, the dissociation of copper sulphate takes place into copper and sulphate. The free copper was deposited over the negative terminal of battery. And the equal amount of copper from the positive electrode gets dissolved in the solution. These process will transfer the copper from one electrode to another electrode.
21) Observe the following circuit given in fig. 14.9.
Fig. 14.9
Current does not in the circuit if there is a gap between the two wires. Does it indicate air is a poor conductor of electricity? Does air never conduct electricity? Explain.
Answer:- yes, Air is bad conductor of electricity. But under a certain conditions such as lighting in bad weather air may conduct electricity.
22) Boojho made the circuit shown in fig. 14.10. 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.
Fig. 14.10
Answer:-
Yes. It will make a difference . If the water taken by boojho is distilled water, and if lemon juice is not added in it, then No current will be passed through it. But if the water taken by boojho is not distilled and slightly salty then a small amount of current will be pass through the circuit and bubbles can be seen on an negative electrode.
23) Observing that the bulb does not glow in the circuit shown in fig. 14.11 A, Boojho changed the circuit as shown in fig. 14.11 B. He observed deflection in the magnetic compass.
Fig. 14.11 A fig. 14.11 B
i) What does the deflection in magnetic compass indicate?
Answer:- the deflection in magnetic compass indicate that there is current in the circuit.
ii) why did the bulb not glow in fig. 14.11 A?
Answer:- the bulb did not glow in fig. 14.11 A due to the insufficient current. The sufficient current was not available to make the bulb glow.
iii) what would be the effect of increase in the number of turns in the coil wound around the magnetic compass in fig. 14.11 B?
Answer:- the increasing in the number of the coil wound around the magnetic compass will also increase in the current and thus the deflection of the magnetic needle will also increase.
iv) what will be observed if the number of cells are increased in the circuit shown in fig. 14.11 B ?
Answer:- if the number of cells are increased in the circuit then the deflection in the compass will also increase .
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.
A B
Answer:-
When the current will flow through the circuit the needle in the magnetic compass will shows deflection due to the magnetic effect of Electric current.