NCERT Solutions for Class 8 Science Chapter 14 Chemical Effects of Electric Current

Ans : (a) Most liquids that conduct electricity are solutions of acids, bases and salts. 
(The solutions of acids, bases or salts are conducting in nature. They allow the current to pass through.) 
(b) The passage of an electric current through a solution causes chemical effects. 
(When an electric current passes through a solution, the solution decomposes into its positive and negative ions. This process of decomposition of the solution is a chemical effect.) 
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery. 
(When an electric current passes through a copper sulphate solution, the solution decomposes into positively charged copper ions and negatively charged sulphate ions. These positively charged copper ions get attracted towards the plate which is connected to the negative terminal of a battery.) 
(d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. 

Ans : The deflection in the compass needle shows that current is flowing through the wounded wire and hence, through the circuit. The circuit is complete since free ends of the tester are dipped in a solution. The solution is certainly a conducting solution. This is the reason why the compass needle shows a deflection. 

Ans : Liquids like lemon juice, salt water and vegetable oil allow electricity to pass through them. Hence, these liquids can be used as in the beaker to show the given effect. 

Ans : The bulb may not glow because of the following reasons: 
(i) Liquid in the beaker is non-conducting. In such case, the electric current would not be able to pass through the liquid. Hence, the circuit is not complete. 
(ii) Electric current in the circuit is very weak. This can happen if the material used for making the circuit is not a good conductor of electricity or the battery does not have sufficient energy to generate electricity. 

Ans : (i) Liquid A is a better conductor than liquid B. 
The amount of current flowing through a conducting solution depends on the conductivity of the solution. With more conductivity, more current passes through the solution and vice-versa. Hence, the conductivity of liquid A is more than the conductivity of liquid B.