CBSE Class 8 Science Chemical Effects of Electric Current Assignment

Question 1. Fill the blanks.

I Fill in the blanks:-

1. A Compound formed by ions is called ________ .

2. The electrode connected to the negative terminal is _________ .

3. Distilled water does not conduct _______.

4. Electroplating is an important use of _______ .

II Choose the correct option:-

1 A liquid metal that conducts electricity :-

(a) Sodium (b) Mercury (c) Lead (d) Gold

2. An atom or a radical that becomes charged is called :-

(a) Radical (b) ion (c) electrode (e) none

3. Metals are extracted from their ores by the process of :-

(a) electroplating (b) electrolysis (c) both (d) none

III Name the following:-

1. An atom that loses an electron

2. Cell used in electrolysis

3. A liquid or a moist paste that has ions in it

IV Define the following:-

1. Electrolysis.

2. Electroplating.

3. Electrolyte.

4. Electrode.

V Draw the following diagrams and label it.

1. Electroplating steel spoons with silver.

2. Flow of ions in an electrolyte.

3. Electrodes.

VI Give reasons for the following:-

1. An acid or ionic salt added to water during the electrolysis of water.

2. Water taps are coated with nickel or chromium.

VII Answer the following in not more than 20 words:-

1. Define anode and cathode.

2. Mercury is a liquid that conducts electricity. What constitutes a current through it ?

VII Answer the following in not more than 40 words :-

1. What happens when a voltage is applied across electrodes placed in an electrolyte ?

IX. Label the diagram and answer the following questions

1. Give a suitable heading to the diagram given below.

2. Name the electrode which collects hydrogen .

3. Name the electrolyte.

4. Write a chemical equation for the process given below.

1.Positive terminal of the cell is indicated by:
(A) The shorter line.
(B) The longer line.
(C) Either of the two lines.
(D) None of these.

2.Symbol of a cell in an electric circuit is represented by:
(A) A longer line and a shorter line.
(B) A longer and a shorter vertical parallel line.
(C) A horizontal longer line and a vertical shorter line.
(D) A vertical longer line and a horizontal shorter line.

3.Battery is having:
(A) Two or more cells connected to each other in any manner.
(B) Positive terminal of one cell is connected to the positive terminal of the next cell.
(C) Two or more cells connected in such a way that the positive terminal of one cell is connected to the negative terminal of the next.
(D) Only one cell.

4.Lines connecting the various components represent:
(A) Wires.
(B) Terminals of the battery.
(C) Battery.
(D) Key.

5.Switch can be connected:
(A) To the positive terminal of the battery only.
(B) Anywhere in the circuit.
(C) To the negative terminal of the battery only.
(D) If required only.

6.When the switch is in the OFF position, the circuit is incomplete. It is said to be:
(A) Open and the current does not flow in the circuit.
(B) Closed and the current flows in the circuit.
(C) Closed and the current does not flow through any part of the circuit.
(D) Closed and the current does not flow through the bulb only.

7.A coil of wire present in electric heater is called:
(A) An element.
(B) A compound.
(C) A mixture.
(D) A solution.

8.In all primary cells chemical energy is changed into…………… energy.
(A) Potential.
(B) Kinetic.
(C) Electrical.
(D) None.

9.Appliance, which do not use electric energy:
(A) Geyser.
(B) Pressure cooker.
(C) Mixie.
(D) Immersion rod.

10.The decomposition of an electrolyte when electricity is passed through it is called:
(A) Electroplating.
(B) Electrolysis.
(C) Conduction.
(D) None.

11.The electrical process of coating an inexpensive conductor with a metal is called:
(A) Electroplating.
(B) Electrolysis.
(C) Conduction.
(D) None.

12.……………..is used in the extraction of metals from their ores.
(A) Electroplating.
(B) Electrolysis.
(C) Conduction.
(D) None.

13.. ………… is used for refining certain metals such as copper and zinc.
(A) Electroplating.
(B) Electrolysis.
(C) Conduction.
(D) None.

14.What is electrolysis?

15.Name the vessel consisting of electrodes and electrolyte in which electrolysis takes place.

16.What is current?

17.Name two sources of electric current.

18.What is meant by an electric circuit?

19.What is a battery?

20.Which type of energy is converted into electrical energy in an electric cell?

21.Which effect of electric current is utilized in electroplating?

22.Why is an acid or an ionic salt added to water in the electrolysis of water?

23.Give one term for each:
(i) The electrode through which current enters the electrolyte.
(ii) The electrode connected to the negative terminal of the battery.
(iii) Purifying metals by using electrolysis.

24.When the switch is in the ON position, the circuit from:
(A) The positive terminal of the battery to the negative terminal is complete.
(B) The circuit is said to be closed.
(C) Current flows throughout the circuit instantaneously.
(D) All of these.

25.The thin wire that glows when current passes through a bulb is called:
(A) Tungsten.
(B) Filament.
(C) Fuse.
(D) Terminal.

26.The bulb gets fused when:
(A) The bulb becomes milky.
(B) The filament is broken.
(C) The glass has broken.
(D) The bulb has become too old.

27.It is unsafe:
(A) To touch a lighted electric bulb.
(B) To carry experiments with electric supply from the mains.
(C) To use electric cells for experiments.
(D) Both (a) and (b).

28.A wire gets _______ when an electric current passes through it.
(A) Weak.
(B) Dull.
(C) Hot.
(D) Cold.

29.The amount of heat produced in a wire depends on its:
(A) Length only.
(B) Thickness only.
(C) Both length and thickness.
(D) Material, length and thickness.

30.The filament of an electric bulb glows on passage of current because:
(A) It has got heated to a high temperature.
(B) It is very thin.
(C) A chemical reaction takes place in the bulb.
(D) All of these.

31.The ISI mark on an electric appliance ensures that:
(A) The appliance is safe.
(B) Wastage of energy is minimum

32.Excessive currents in electrical circuits are the consequence of:
(A) Direct touching of wires.
(B) Connecting many devices to a single socket.
(C) Faulty wiring.
(D) All of these.

33.The needle of a compass:
(A) Is a tiny magnet that rests in North - South direction.
(B) Gets deflected when a magnet is brought close to it.
(C) Gets deflected when current flows in a nearby wire.
(D) All of these.

34.Magnetic effect of the electric current:
(A) Means that a wire behaves like a bar magnet on passage of electricity.
(B) Is utilized to make magnets.
(C) Was first observed by Hans Christian Oersted.
(D) All are correct.

35.Which one is good conductor of electricity:
(A) Wood.
(B) Glass.
(C) Silver.
(D) Plastic.

36.Which one is bad conductor of electricity:
(A) Wood.
(B) Copper.
(C) Silver.
(D) Gold.

37.The process of depositing a layer of any desired metal on another material by means of electricity is called:
(A) Electroscoping.
(B) Electroplating.
(C) Both.
(D) None.

38.Which one is not a source of electric current:
(A) Voltaic cell.
(B) Daniel cell.
(C) Battery.
(D) None.

39.An electrode connected to the negative terminal of a battery is called:
(A) Anode.
(B) Cathode.
(C) Pole.
(D) None.

40.An electrode connected to the positive terminal of a battery is called:
(A) Anode.
(B) Cathode.
(C) Pole.
(D) None.

41.A compound formed by ions is called an …………. Compound.
(A) Metallic.
(B) Ionic.
(C) Covalent.
(D) None.

42.A metal is released in the electrolysis of a salt. At which electrode will it be deposited?
(A) Anode.
(B) Cathode.
(C) Both.
(D) None.

43.What is the full form of 'LED'

44.Does pure water conducts electricity? It not what can we do to make it conducting

45.Name the products formed when electricity passes through distilled water

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46.What do you understand by the term magnetic effects of an electric current?

47.What do you understand by the term chemical effects of an electric current?

48.What is a conductor? Give two examples.

49.What is an insulator? Give two examples.

50.What do you mean by the term electroplating?

51.Write some applications of the chemical effect of current.

52.What makes LED more useful for testing the flow of current.

53.Why it is dangerous to touch on electrical appliance with a wet hand?

54.A child staying in coastal region tests the drinking water and also the seawater with his tester. He finds that compass needle defects more in the case of sea water. Can you explain the reason?

55.State two applications of electrolysis.

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56.What is an electrode? What are cathode and anode?

57.What are dangers of electricity?

58.Write some points that should be remember while electroplating.

59.Write some uses of electroplating.

60.List three conditions that help to ensure a smooth and firm deposit during electroplating.

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61.What is electroplating? How are steel spoons plated with silver? Explain with the help of diagram.

62.An experiment was set as shown below:

(i) Label the parts indicated by arrows in diagrams.
(ii) Will the bulb glow if the sodium chloride is in:
(a) Solid state?
(b) Molten state?
(c) Aqueous state?
Explain your answer. .

63.Describe an activity to show that current flowing through solutions produce a magnetic effect

Question 1. Fill the blanks.

 

1. Veena has read that some substances are good conductors of electricity where as some are bad conductors. Among the following which substance is good conductor of electricity?

Q1. Do liquids also conduct electricity? Name two liquids which conduct electricity & two liquids which do not conduct electricity.

Q2. Name a device which glows even when a weak electric current passes through it.

Q3. Write full form of LED.

Q4. Which effect of electric current is utilized for detecting the flow of current through a solution:

a) When a torch bulb is used?

b) When a compass is used?

Q5. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Q6. When electric current is passed through acidified water, then hydrogen & oxygen are formed. What type of effect of current is illustrated by this statement?

Q7. State some of the characteristics of chemical changes brought about by the chemical effect of electric current.

Q8. Name the metal which is usually electroplated on car parts such as bumpers & bicycle handlebars made of steel.

Q9. An iron key is to be electroplated with copper. Draw a labeled sketch of the experimental set up used for this purpose.

Q10. Name two metals which are usually electroplated on cheaper metals for making jewellery (or ornaments).

Q11. You are required to do electroplating of copper on an iron object. Name the positive electrode (anode) & the electrolyte you will use for this purpose.

Q12. Write a short note on electroplating.

Q13. Why does compass needle show more deflection when you test sea water, compared to ordinary water?

Q14. Name a liquid which when poured in the beaker may cause magnetic needle to deflect. Name the possibilities if a bulb in tester does not glow (it is for sure that liquid is conducting).

Q15. What happens to the needle of a magnetic compass kept nearby when electric current is switched on in a wire? Why does this happen?

Q16. Iron is used in bridges & automobile to provide strength. Which metal is electroplated on iron to protect it from corrosion?

Q17. We should never handle electrical appliances with wet hands or while standing on a wet floor. Why?

Q18. When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into the following solution, then in which solution or solutions the compass needle shows deflection. Solutions are: Lemon juice, Vinegar, Tap water, Vegetable oil, milk, Honey.

Q19. Why does an electric bulb glow when a current passes through it?

Fill in the blanks:

1. Distilled water is _____________ of electricity.

2. The dissociation of chemicals into ions due to the passing of electricity through it is the _____________ of electricity.

3. The distilled water becomes _____________ of electricity on dissolving salt in it.

4. _____________ are wires/rods/plates through which electricity enters of leaves an electrolyte.

5. The longer lead of LED is always connected to the positive terminal of the battery.

6. Name two liquids that conduct electricity _____________.

7. The passage of electric current through liquids causes _____________.

8. Coating of _____________ is deposited on iron to protect it from corrosion.

9. What is LED

10. Define Electroplating

11. Name some materials around you which conduct electricity.

12. Name some materials around you which do not conduct electricity.