The presence of electric current can be detected by the various effects which it produces. The obvious effects of the current are:
(i) Heating effect
(ii) Magnetic effect
(iii) Chemical effect
Heating Effect
Current flows through a metallic wire due to motion of free electrons. During the course of their motion, they collide frequently with the atoms of the metal. At each collision, they lose some of their kinetic energy and give it to atoms with which they collide. Thus as the current flows through the wire, it increases the kinetic energy of the vibrations of the metal atoms. i.e., it generates heat in the wire. It is found that the heat H produced by a current / in the wire of resistance R during a time interval tis given by
H=I2Rt
The heating effect of current is utilized in electric heaters, kettles, toasters and electric irons etc.
Magnetic Effect
The passage of current is always accompanied by a magnetic field in the surrounding space. The strength of the field depends upon the value of current and the distance from the current element. The pattern of the field produced by a current carrying straight wire, a coil and a solenoid is shown in Figure. Magnetic effect is utilized in the detection and measurement of current. All the machines involving electric motors also use the magnetic effect of current.
Chemical Effect
Certain liquids such as dilute sulphuric acid or copper sulphate solution conduct electricity due to some chemical reactions that take place within them. The study of this process is known as electrolysis. The chemical changes produced during the electrolysis of a liquid are due to chemical effects of the current. It depends upon the nature of the liquid and the quantity of electricity passed through the liquid.
The liquid which conducts current is known as electrolyte. The material in the form of wire or rod or plate which leads the current into or out of the electrolyte is known as electrode. The electrode connected with the positive terminal of the current source is called anode and that connected with negative terminal is known as cathode. The vessel containing the two electrodes and the liquid is known as voltameter. As an example we will consider the electrolysis of copper sulphate solution. The voltameter contains dilute solution of copper sulphate. The anode and cathode are both copper plates.
When copper sulphate is dissolved in water, it dissociates into Cu++ and SO4--, ions. On passing current through the voltameter. Cu moves towards the cathode and the following reaction takes place.
Cu+++2e-- -------> Cu
The copper atoms9 thus formed are deposited at cathode plate. While copper is being deposited at the cathode, the SO, ions move towards the anode. Copper atoms from the anode go into the solution as copper ions which combine with sulphate ions to form copper sulphate.
Cu+SO -----> CuSO
As the electrolysis proceeds, copper is continuously deposited on the cathode-while an equal amount of copper from the anode is dissolved into the solution and the density of copper sulphate solution remains unaltered.
This example also illustrates the basic principle of electroplating a process of coating a thin layer of some expensive metal (gold, silver etc.) on an article of some cheap metal.
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