Ncert solutions science class 8 Solutions for Chapter 14 chemical effects and electric current

Q1) 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 _____________ .

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 _________.

An electric current can produce

(a) heating effect only.

(b) chemical effect only.

(c) magnetic effect only.

(d) chemical, heating, and magnetic effects.

When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in Fig.

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.

Q2) When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

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.

Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

Q3) Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

When an electric current is passed through a conducting solution, there is a change of color 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.

Q4) The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.

The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.

Which one of then following solutions will not conduct electricity?

(a) lemon juice

(b) vinegar

(c) tap water

(d) vegetable oil

Q5) 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.

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.

Q6) Does pure water conduct electricity? If not, what can we do to make it conducting?

Does pure water conduct electricity? If not, what can we do to make it conducting?

Which of the following metals is used in electroplating to make objects appear shining?

(a) iron

(b) copper

(c) chromium

(d) aluminium

Which of the following solutions will not make the bulb glow?

(a) sodium chlorides

(b) copper sulphate

(c) silver nitrate

(d) sugar solution in distilled water

Q7) 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.

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.

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.

Q8) 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?

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?

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

Q9) Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Why is a layer of zinc-coated over iron?

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?

Q10) 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?

Will the solution of sugar in distilled water conduct electricity?

Q11) Prepare a list of objects around you that are electroplated.

Prepare a list of objects around you that are electroplated.

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

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 transfered to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

Q12) 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 transfered to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

Boojho made the circuit given in Fig. 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.

Paheli set up an experiment using liquid A in the beaker as shown in Fig. 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.

Paheli wants to deposit silver on an iron spoon. She took a silver nitrate (AgNO3) solution in a beaker and set up 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?

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

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.

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

In the circuit given as Fig, 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 a negative electrode. Will copper be still deposited on the carbon rod? Explain your answer.

Observe the circuit given in Fig.

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

Observe the following circuit given in Fig.

The 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.

Boojho made the circuit shown in Fig. 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.

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.

(i)What does the deflection in magnetic compass indicate?

(ii) Why did the bulb not glow in Fig.14.11 A?

(iii) What would be the effect of an increase in the number of turns in the coil wound around the magnetic compass in Fig. 14.11B?

(iv) What will be observed if the number of cells are increased in the circuit shown in Fig. 14.11B?

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.