Chapter 20: ELECTRICITY AND CIRCUITS

Conductors and Insulators

Conductors –Allow electricity to pass through them. Due to free electrons present on their surface. [Metals, Human body]

Insulators – Don’t allow electricity to pass through them. [Air]

Pure water doesn’t conduct electricity. Most of the acids, bases and salts are conductors. When electrodes are dipped in water and an electric current is passed through it, Oxygen bubbles formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles formed on the other electrode.

Effects of Electric current

Heating effect of electric current is used in geysers, heaters, irons etc. The heating produced in a wire depends on its material, thickness, length. Bulbs have filament of tungsten that emits light when heated at high temperatures, it is also filled with inert gas like nitrogen or argon.

Magnetic effect of current was discovered by Hans Oersted. This principle is used in electromagnets, electric bells.

Uses of Electric current

Electroplating is a common application of chemical effects of electric current.

e.g.: Chromium doesn’t rust or scratch so a metal is coated with chromium for utensils, tin is coated on iron in tin cans so food doesn’t come in contact with iron. Iron objects are coated with zinc to prevent corrosion "Galvanization" .

Corrosion is an oxidation reaction.

Oily foods get oxidized if kept in the open and their taste changes [rancidity], due to this they are kept in air tight containers. Hence, Chips bags are flushed with nitrogen to prevent oxidation.

AC current can be transmitted farther than DC without much loss of electrical energy.

Household devices are connected in parallel.

Fuel Cells

Fuel cells use reaction of oxygen and hydrogen, porous carbon electrodes and aqueous solution of NaOH. Platinum or palladium electrodes are used as catalysts.
 

Q.With reference to ‘fuel cells’ in which hydrogen-rich fuel and oxygen are used to generate electricity, consider the following statements :
1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products.
2. Fuel cells can be used for powering buildings and not for small devices like laptop computers.
3. Fuel cells produce electricity in the form of Alternating Current (AC).
Which of the statements given above is / are correct? (UPSC CSAT 2015)

• 1 only




• 2 and 3 only




• 1 and 3 only




• 1, 2 and 3

Ans . A

1. The purpose of a fuel cell is to produce an electrical current that can be directed outside the cell to do work, such as powering an electric motor or illuminating a light bulb or a city.

2. One great appeal of fuel cells is that they generate electricity with very little pollution–much of the hydrogen and oxygen used in generating electricity ultimately combines to form a harmless byproduct, namely water alongwith releasing heat.

3. A single fuel cell generates a tiny amount of direct current (DC) electricity. In practice, many fuel cells are usually assembled into a stack. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter.

Official YouTube Channel of UPSCFEVER - #1

Quiz

Score more than 80% marks and move ahead else stay back and read again!