NCERT solutions for Science Exemplar Class 8 chapter 14 - Chemical Effects of Electric Current [Latest edition]

An electric current can produce

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

Boojho's Experiment	Paheli's Experiment
(A)	(B)

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 uncle has set up an electroplating factory near his village. He should dispose off, the waste of the factory

When electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates

Which one of the following solutions will not conduct electricity?

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

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

The object to be electroplated is taken as ______ electrode.

One of the most common applications of chemical effect of electric current is ______.

Small amount of a mineral salt present naturally in water makes it a ______ of electricity. 

Electroplating of ______ is done on objects like water taps and cycle bell to give them a shiny appearance.

Why is a layer of zinc coated over iron?

Will the solution of sugar in distilled water conduct electricity?

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

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.

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

Paheli wants to deposit silver on an iron spoon. She took 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 figure.

A	B

Which of these two circuits A or B shows the correct observation? 

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 figure.

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

In the circuit given in the 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.

Observe the circuit given in the figure.

Boojho set up this circuit for purification of copper. What will be the nature of – (a) plate A (b) plate B (c) and the solution.

Explain the process of purification.

Observe the following circuit given in the 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.

Boojho made the circuit as shown in the 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.

Observing that the bulb does not glow in the circuit shown in Fig. (A) Boojho changed the circuit as shown in Fig. (B). He observed deflection in the magnetic compass.

A	B

1. What does the deflection in magnetic compass indicate?
2. Why did the bulb not glow in Fig. (A)?
3. What would be the effect of increase in the number of turns in the coil wound around the magnetic compass in Fig. (B)?
4. What will be observed if the number of cells are increased in the circuit shown in Fig. (B)?

You are provided with a magnetic compass, an empty matchbox, 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.