(a) _______, _______ and _______ are the liquids that conduct electricity.
(b) _______ is the effect generated when an electric current is passed through a solution.
(c)_______ is known as the process for depositing a layer of any metal on another material by the means of Electricity.
(a) Acids, Bases and Salts.
2. Explain; Why a magnetic needle shows deflection, when the free end of a tester are dipped into a solution?
The compass needle shows a deflection which concludes that current is flowing through the wire. The circuit becomes complete as the free ends of the tester are immersed inside the solution. So, the solution is conducting solution and that is the reason why a deflection is obtained in the compass needle.
3. Name three liquids which may cause a deflection in the magnetic needle when tested in a manner shown below.
II. Lemon juice
III. Vegetable oil
These liquids can be taken in a beaker to show the passage of electricity as they will show a deflection in the magnetic needle.
4. The bulb does not glow in the setup shown below. List the reasons and explanations.
The possibility of the bulb not glowing maybe because of the following reasons:
a. The liquid is non-conducting. In this case, the circuit is incomplete and the current does not pass through the liquid.
b. Electric current is weak. If the circuit is made up of a material which is not a good conductor of electricity or there is insufficient energy in the battery to generate electricity.
5. In order for checking the conduction of electricity through two liquids, A and B a tester is being used. It is found that the tester bulb glows brightly for liquid A and Very dimly for liquid B. Which of the two liquids are better in conducting electricity?
Liquid A is a better conductor than liquid B.
The conductivity of the solution determines the amount of current flowing through the solution. Greater the conductivity, greater will be the quantity current passing through the solution and lesser the conductivity, the quantity of current passing through will be correspondingly less. So, the conductivity of liquid A is more than the conductivity of liquid B.
6. What can we do to make pure water to conduct Electricity?
Pure water does not conduct electricity as it does not contain any type of salts. Adding, a small amount of Common salt (Sodium Chloride ie,.NaCl) will turn the water to a conducting medium. It is because the salt solution is conducting in nature.
Why in case of a fire, the main electrical supply is turned off before the firefighter uses the water hoses.
The water sprayed from the hose might conduct electricity and if the current supply or the area is not shut off, the water that is being poured in may come in contact with the electrical appliances, there is a very high chance that electricity may pass through the water and hurt the firemen. To avoid such harm, the firemen shut off the main electrical supply for the area before pouring water.
Why the compass needle deflects more in seawater as compared with drinking water?
The amount of dissolved salts present in the seawater is more than that of the drinking water. So, the sea water will be a better conductor than the drinking water. That is the reason behind the increased deflection of the needle in the seawater when compared with the drinking water.
10. Is it safe for an electrician to carry out repairs outdoors during heavy downpour?
No. It is not safe to repair electrical appliances outdoors during a heavy downpour. Rainwater is composed of a certain percentage of dissolved salts making it conductive. This may cause electric shocks and harm the electrician while working outdoors during heavy downpours.
11. We know that rainwater is pure. But when we test it, the compass needle shows deflection. Why so?
Dissolved salts form a certain percentage in the composition of rainwater and this makes the water to conduct electricity. Distilled water is free from such salt content. So, rainwater permits current to flow through it whereas distilled water doesn’t.
12. Make a list of objects that are electroplated.
Chromium plating: This is done on exterior parts of automobiles in order to obtain a shiny appearance.
Gold Plating: Silver ornaments are coated with a thin layer of gold and the product are called Gold-plated Ornaments.
Zinc Plating: Iron used for Construction and other such purposes are coated with a Zinc layer in order to protect them from corrosion and rusting.
13. A thin plate of copper and a thick rod of impure copper are used as electrodes in the process of purification of copper and the diagram for the process is given below. Cathode from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?
Copper ion has a positive charge. The negative terminal attracts positive copper ions. As copper ions move towards the thin copper plate. This pure copper plate should be connected to the negative ends. Likewise, the positive terminal of the battery is connected with the impure copper rod.
Class 8 is one of the crucial stages of a student’s life, students of class 8 will be writing national level exams like science Olympiad and other scholarship tests. The NCERT solutions provided here for chapter chemical effects of electric current will help the students to learn the concepts in an easy way.
This chapter deals with the chemical effects of electric current, electroplating, good conductors, LED and conductors. The topics provided in this chapter are very important from the point of examination.
Along with NCERT solutions, students should practice lots of sample papers and previous year questions. Solving previous year questions and sample papers will help them to know about different types of questions asked in the examination.