Electricity: Conductors, Insulators, Electric Charge - PDF

Okay, here's the conversion of the document into a markdown format. I'll do my best to capture the information accurately. # Electricity ## Introduction Objects around us are made up of matter, and matter is made up of *atoms*, which contain *electrons, protons, and neutrons*, called **subatomic...

Okay, here's the conversion of the document into a markdown format. I'll do my best to capture the information accurately. # Electricity ## Introduction Objects around us are made up of matter, and matter is made up of *atoms*, which contain *electrons, protons, and neutrons*, called **subatomic particles**. Out of these three subatomic particles, *electrons* and *protons* have special properties due to which they interact with each other; this property is called **electric charge**. The word '*Electricity*' means the transfer of energy from one point to another with the help of moving charges. ## Types of Electric Charges In nature, there are two types of electrical charges: positive and negative. A proton carries a *positive* charge; an electron carries a *negative* charge, and the neutron has no charge; i.e., it is neutral. Protons and neutrons reside in the nucleus of an atom, while the electrons revolve around the nucleus in paths called orbits. In an atom, the number of protons is equal to the number of electrons. Since the total positive charge and negative charge are equal, an atom is called *electrically neutral*. The $SI$ unit of electric charge is the *coulomb (C)*. The coulomb has been named in the honour of French physicist *Charles Augustin de Coulomb (1736-1806)*. The amount of charge on an electron or proton is denoted by '*e*' and is called the **elementary charge**, where $e=1.6 \times 10^{-19}$ coulombs. Hence, both electron and proton have the same magnitude of charge upon them; that is, the elementary charge '*e*' with the electron has a negative charge and the proton has a positive charge. The charge on a single electron and proton is so small that to build up a charge of $1 C$, we would require $6.25 × 10^{18}$ electrons or protons in excess on any substance. Thus, $1C = 6.25 × 10^{18}$ electrons An atom can be charged or made to become non-neutral by the following methods given below: **(a)** If an atom gains electrons (i.e., it now has more electrons than protons), it becomes negatively charged *(anion)*. **(b)** If an atom loses electrons (i.e., it now has more protons than electrons), it becomes positively charged *(cation)*. **NOTE:** Charged particles (atoms carrying electric charge) are called *ions*. ## Properties of Electric Charge **(i)** Like charges repel each other, and unlike charges attract each other. **(ii)** The sum of all the charges on a body along with their polarity sign is called the *net charge* on it. **(iii)** Charge on a body is always quantized; i.e., charge on a body will always be in integer multiple elementary charge (e). Thus, $Charge \quad on \quad a \quad body (Q) = \pm n \times e $ **Figure:** *Interaction of Charges* show like charges repelling and opposite charges attracting. Where, $n$ is the number of elementary charge particles (electron or proton), $e$ is the magnitude of the elementary charge $(1.6 \times 10^{-19} C)$ and $Q$ is the net charge on the body. **(iv)** Electric charge is a scalar quantity. **(v)** Electric charge on a system is always conserved; i.e., charge can neither be created nor destroyed. **(vi)** A neutral body can become positively charged by losing electrons, and another neutral body can be negatively charged by gaining excess electrons. The process of losing or gaining electrons is called *charging a body*. ## Charging a Body by Friction Whenever two bodies (at least one non-conductor) are rubbed against each other, heat is produced due to friction present between them. Due to this heat produced, electrons in both the bodies are excited and come out of their parent atom. The body having more electron affinity attracts some of the electrons from other bodies. Both the bodies develop equal and opposite charges by this method. The body, which gains excess electrons, becomes negatively charged and the body, which loses electrons, now becomes deficient in electrons, hence becomes positively charged. For example, when we comb dry hair, the comb gets negatively charged and can pick small pieces of neutral paper brought near it. Similarly, when a balloon is rubbed with dry hairs, it becomes negatively charged and attracts positively charged or neutral bodies. **NOTE:** A charged body will always attract a neutral body. "A comb attracting small pieces of paper" ## Conductors and Insulators Substances which allow charges to flow through them are called **conductors**. Conductors have free electrons due to which they conduct electricity. All metals are generally good conductors of electricity, with Gold the best conductor of electricity, followed by Silver, Copper, aluminum, etc. In non-metals, Graphite, all kinds of electrolytic solutions (Aqueous solutions of $NaCl, HCl, H_2SO_4$ etc.), and tap water are good conductors. The substances which do not allow the electric charges to flow through them are called **insulators**. They do not have free electrons. Some examples of insulators are rubber, glass, wood, plastics, porcelain, pure distilled water, sugar, etc. Vacuum is the best insulator. Water with salt conducts electricity such as tap water due to presence of free ions in them and distilled water will not conduct electricity due to absence of free ions. Ions are the electrically charged atoms or group of atoms. A positively charged ion is called *cation* and a negatively charged ion is called *anion*. There are substances whose conductivity lies in between the conductors and insulators that are called **semiconductors**. For example, silicon, germanium are semiconductors. A semiconductor may become a conductor by increasing its temperature. Such substances are used to create electronic circuits like computer chips. ## Try it Yourself 1. What is the SI unit of electric charge? 2. The charge on an object is given by $q = ne$, where $n$ is the number of electrons and $e$ is the elementary charge. If an object has charge $-2 \times 10^{-19} C$, what should be the number of excess electrons on it? 3. If an atom has a charge of $-5C$, then how many excess electrons must it have? 4. What is electricity? 5. What do you mean by net charge on a body? 6. A body has 25 protons and 15 electrons, what is the net charge on this body? 7. What is a conductor of electricity? What is the best conductor of electricity? 8. What is the ratio of magnitude of charge on the silk cloth and glass rod after they are rubbed together? ## Electric Current The flow of electric charges through a conductor or electrolyte is called *electric current*. An electric current is defined as the charge flowing through a point per unit time. When $Q$ coulombs of charge flow through a point in $t$ seconds, the current $I$ at that point is: $I = \frac{Q}{t}$ The unit of electric current is coulomb/second, and it is also called *ampere*, denoted with symbol A. This is the SI unit of electric current. The ampere has been named in the honour of the French physicist and mathematician *Andre Marie Ampere (1775-1836)*. ## Electric Cell An electric cell is a device used to provide electricity on a very small scale, for example, to a remote control, lighting a small bulb, watches, etc. An electric cell converts chemical energy into electrical energy (electricity). Generally, an electric cell has two terminals, positive and negative. When these terminals are connected with a wire, either directly or indirectly through some other electrical device (like a bulb), current flows through the wire from the positive to negative terminal of the cell. When more than one cell are connected together, it makes a battery. * Schematic diagram of circuit with battery and bulb. ## Direction of Electric Current In earlier days of discovery of electric charge, electrons were not discovered. It was considered that flow of current is due to the flow of positive charges, and the direction of flow of the positive charge was taken as the direction of electric current. Thus, it was believed that the current flows from the positive terminal to the negative terminal of a cell, and this direction is called the *conventional direction of electric current*. But after the discovery of electrons by J.J. Thomson, it was found that only electrons can flow through the conducting wires as protons are bound to the nucleus of their atom and hence cannot move. However, in electrolytes, both positive and negative charges move in opposite directions in the form of ions. ## Flow of Electric Current in a Wire An electric current is the flow of electrons in a metal wire (or a conductor) when a cell or battery is applied across its ends. A conductor has free electrons in it. Inside the wire, electrons, in the absence of any electric source like a cell, move randomly between the atoms of the metal wire. ## Electric Circuit A continuous conducting path through which electric current can flow is called an electric circuit. A circuit may consist of various electric devices like a bulb, switch, resistors, etc., connected with each other through conducting wires and to the terminals of a source like a cell or a battery. Circuits can be of two Types: **(i) Closed circuit:** A closed continuous conducting path through which electric current can flow is called a closed electric circuit. **(ii) Open circuit:** A conducting path that is not continuous and through which electric current cannot flow is called an open electric circuit. The image depicts open and closed circuits with diagrams. Both circuits include a Bulb, Cell, Connecting Wire and Switch. The open circuit shows the switch open, meaning the electric current cannot flow. The closed circuits shows the switch closed, meaning the electric current can flow. ## Electrical Conductivity Electrical conductivity is a measure of the ability of a substance to carry electric current. Substances that are good conductors of electricity have high electrical conductivity as compared to substances that are poor electrical conductors (also called insulators). Some liquids, but not all, are also good conductors of electricity. **(i) Conductivity of Water:** Pure water or distilled water is a poor conductor of electricity due to the absence of free ions in it. But if water contains salts, it conducts electricity due to the presence of free ions in the water. Water we use in our houses is not pure water. Generally, water (tap water, pond water, well water, etc.) contains a lot of impurities, most of which are usually dissolved salts. Presence of even a small amount of impurity makes water a good conductor of electricity. Touching an electrical appliance with wet hands could, therefore, be dangerous. **(ii) Conductivity of Other Liquids (Lemon Juice):** A lemon is a citrus fruit, an excellent source of Vitamin C and makes a cool and refreshing summer drink. But did you know we can generate electricity using a lemon? Lemon juice contains an acid called citric acid. To test the electrical conductivity of lemon juice, we arrange four to five lemons using strips of copper and zinc, a few alligator clips and connecting wires. The electricity produced is although not very much but is enough to light a small LED (Light emitting diode). ## Activity **Aim:** We can make a simple tester to check whether a substance is a conductor or insulator of electricity using a bulb and cell. **Materials required:** small electric bulb, a cell and some wires. **Methodology:** Take some wire and connect them with the cell and bulb. By touching the remaining two ends of the wires to a substance, we can check whether the given substance is a conductor or insulator. If the bulb glows, that means the substance is conducting electricity; otherwise, not. The image shows an "Electric conductivity tester circuit". We can also use an LED (light-emitting diode) in place of a bulb with a resistance. In that case, just replace the bulb with an LED with a resistor. **LED (Light Emitting Diode):** It is similar to a bulb, but it runs on very low electricity and requires a very small amount of current to glow as compared to a bulb. The coloured lights that we see in decorations, LED Bulbs, and even in the screens of some mobile phones are all LEDs. It has two leads: one is longer & the other is shorter. The longer lead is connected to the positive terminal and the shorter lead is connected to the negative terminal of the cell / battery. ## Activity We can make a similar tester as we discussed in the previous activity to check whether a substance is a conductor or insulator of electricity using some wires and a magnetic compass. **Materials required:** magnetic compass, a cell and some wires. **Methodology:** Take some wire and wrap it around the magnetic compass and connect the cell/battery at one end. With the remaining ends of the wire, we can now test for conductivity of any substance. We just need to touch the remaining ends of wires with the substance to be tested. If the substance under test is a conductor, the electric current will flow through the substance and through the wire, the magnetic compass will deflect. Thus, we get to know that it is a conductor. Otherwise, if the substance is an insulator, then no current will flow and there will be no deflection in the compass needle. The image shows an "Electric conductivity tester using magnetic compass". ## Chemical Effects of Electric Current We know in solids electric current flows due to the movement of electrons while in liquids, electric current flows because of movement of negative and positive ions. For example, table salt (sodium chloride) is made of sodium ions (+ve ions) and chloride ions (-ve ions) that are fixed in place and cannot move through the solid phase. But when salt is dissolved in water, the sodium and chloride ions break apart and spread out evenly in the water, forming a solution. Now the positive and negative ions are free to move. Thus, liquids containing ions can conduct electricity. ## Electrolysis The process due to which a solution of a chemical compound *conducts electricity* and *undergoes a chemical change* is called **electrolysis**. Some general terms associated with electrolysis: **(i) Electrolyte:** A solution of a chemical compound which conducts electric current and undergoes a chemical change is called an electrolyte. For example, aqueous solutions of all acids such as $HCl$, $HNO_3$, $H_2SO_4$ etc. Aqueous solutions of all alkalis such as $NaOH$, $KOH$ etc. Aqueous solutions of salts such as common salt, copper sulphate, sodium nitrate, zinc chloride etc. **(ii) Non-electrolyte:** A solution of a chemical compound which does not conduct electric current and hence does not undergo any chemical change is called non-electrolytes. For example: Petrol, kerosene oil, diesel oil, vegetable oil, alcohol, distilled water etc. **(iii) Electrodes:** Conductors through which the current enters or leaves an electrolytic solution are called electrodes. It can be wires, plates, rods, etc. **(iv) Cathode:** The electrode connected to the negative terminal of a cell/battery is called the cathode. **(v) Anode:** The electrode connected to the positive terminal of a cell/battery is called the anode. **(vi) Ions:** The electrically charged atoms or groups of atoms formed when a chemical compound dissolves in water. **(vii) Cations:** The positively charged ions formed when a chemical compound dissolves in water. During electrolysis, the cations are discharged at the cathode by taking electric charges from it. **(viii) Anions:** The negatively charged ions formed when a chemical compound dissolves in water are called anions. During electrolysis, the anions are discharged at the anode by losing electric charges to it. **(ix) Voltmeter:** An apparatus in which electrolysis is carried out, which consists of a vessel, two electrodes, and electrolyte is called a voltmeter. When electric current through a conducting solution causes chemical reactions to occur. A small amount of $H_2SO_4$ acid is added to increase the conductivity by increasing the number of free ions in the solution. As a result, bubbles of a gas will be formed on the electrodes. Deposits of metal may be seen on electrodes. Changes of color of solution may occur. The reaction will depend upon what solution and electrodes are used. This is the chemical effect of electric current when it is passed through impure water. The chemical reaction involved in the electrolysis of water is given by: ${2H_2O} \overset{Electrolysis}{\longrightarrow} 2H_2 + O_2$ (Image: Electrolysis of water with H2SO4) illustrates components of electrodes. ## Electroplating Electroplating is the most common application of electrolysis. It is used for coating thin layers of metals like *copper, nickel, silver, gold, zinc*, etc. on the surface of other metals or alloys. The process of depositing a thin and uniform layer of a metal on any conducting surface is called "electroplating". **(i)** In this process, the conducting material to be electroplated is made 'cathode', and the metal whose coating is required on the cathode material is used as anode. **(ii)** A soluble salt which contains ions of the anode material are is taken as an electrolyte when the current is passed through the circuit; the following reactions take place. The image shows an electroplating apperatus. ## In relation to the Anode and Cathode **(iii)** At the anode, oxidation of metal atoms to be coated on the cathode material takes place. ${M \longrightarrow M^{p+} + pe^-}$ Where p is the no. of electrons lost or gained. **(iv)** At the cathode, the reduction of these ions takes place and their atoms get deposited on the cathode. ${MP+ + pe^- \longrightarrow M}$ **Figure**: *Electroplating of copper on iron nail* Uses of Electrolysis: **(i)** Electroplating: It is one of the most common uses of electrolysis. The wheel covers of cars, the handles of bicycles and motorcycles are coated with nickel and chromium, so as to give a bright shining appearance. Similarly, silver and gold can be electroplated on copper and brass objects. Cheap imitation jewelry is made by electroplating silver or gold on brass or aluminum jewelry. Protective coating of zinc on copper, Iron or steel is used to prevent them from rusting with the help of electroplating; this process is called **galvanization**. **(ii)** Electrolysis is also used to obtain pure metals from impure metals. **(iii)** Electrolysis is also used to extract metals from their ores. ## Safety Measures While Using Electricity A strong electric shock can give the body a big shock which can damage cells of the body. If the current happens to pass through the heart, it causes the heart muscles to contract which may cause heart attack and death may occur. So it is very important to be cautious while handling electrical appliances. Electricity could turn dangerous due to loose connections in switches, improper wiring, overloading (passing of excess current above the rated capacity of an electrical appliance) and improper earthing. Below are some safety precautions we should follow while using electrical appliances: **(i)** Good quality wires with proper insulation should be used for wiring in homes. **(ii)** Defective, damaged plugs, sockets, wires, and switches should be replaced immediately. **(iii)** Switches and plugs should not be touched with wet hands. **(iv)** The main switch should be immediately switched off in case of fire, overloading, or short circuit. **(v)** All appliances should be properly provided with Earth connection. **(vi)** Rubber-soled shoes should be worn while repairing electrical appliances; this protects us from electric shocks. **(vii)** The inside of a socket should not be touched as it is made up of conductive material, which can give a shock. Let me know if you need any adjustments or further assistance!