Contents
Physics Topics cover a broad range of concepts that are essential to understanding the natural world.
What are Conductors and Insulators ? And How Can you Check if a Substance is Conductor or an Insulator?
Some materials allow electric current to pass through them whereas other materials do not allow an electric current to pass through them. On the basis of this property, we can divide all the materials around us into two groups: conductors and insulators. We will now study the conductors and insulators in detail, one by one. Let us start with the conductors.
Conductors
Those materials which allow electric current to pass through them are called conductors (of electricity). The flow of electric current is called electricity. So, we can also say that: Those materials which allow electricity to pass through them are called conductors (of electricity). All the metals are conductors of electricity. Silver metal is the best conductor of electricity. Copper and aluminium metals are also good conductors.
Electric wires are made of copper and aluminium because they are conductors of electricity. Other metals like iron, steel, mercury and gold, etc., are also conductors. The metal alloys (like steel, brass and bronze, etc.) are also conductors of electricity. All the objects made of metals (or metal alloys) are also conductors.
For example, the objects such as coins, keys, pins, aluminium foil, sewing needle, and iron nail, etc., are all conductors of electricity (because they are made of metals or their alloys). A non-metal called carbon (in the form of graphite) is also a conductor of electricity. The thin, black core of our pencil is called pencil lead. Pencil lead is made of graphite. So, pencil lead is a conductor of electricity.
The human body does not conduct electricity as good as metals. The human body conducts electricity to a small extent. So, the human body is a poor conductor of electricity. A person gets electric shock on touching an uncovered electric wire carrying current because some electric current passes through his body. Water also conducts electricity to a small extent.
So, water is also a poor conductor of electricity. If a person operates an electric switch with wet hands, he can get an electric shock because water present on the wet hand can conduct some electricity from the switch into his body. We should, therefore, operate the switches of electrical appliances with dry hands.
Insulators
Those materials which do not allow electric current to pass through them are called insulators. In other words, those materials which do not allow electricity to pass through them are called insulators. Insulators are actually the non-conductors of electricity. Rubber, plastics (like polythene, PVC and bakelite), ceramics, porcelain (china, etc.), asbestos, wood, glass, mica, cotton, jute, thermocol, wax, paper, air and most of the gases are insulators.
They do not allow electric current to pass through them. All the objects made of insulator materials are also insulators. For example, rubber is an insulator, therefore, an eraser and balloon (made of rubber) are also insulators. Wood is an insulator, so a wooden block, cork and matchstick (made from wood) are also insulators. Plastic is an insulator, therefore, a plastic scale, polythene bags and nylon socks (made of plastics) are also insulators.
Similarly, a candle (made of wax) and a glass bangle (made of glass) are also insulators. The outer covering of electric wires is made of plastic because plastic is an insulator. Plastic covering does not allow electric current to pass through it. Air is an insulator. In other words, air is a non-conductor of electricity.
When an electric switch is in the “off” position, then air is present between the ends of the wires connected to the switch. Since air is a non-conductor of electricity (or insulator), electricity is not conducted across the gap between the ends of the wires in the switch and hence the bulb does not light up.
We will now describe an activity to find out whether a given material conducts electricity or not. This will tell us whether a given material is a conductor or a non-conductor (insulator). Please note that the dry cell (used in torches) will be the source of electric current (or electricity) for the activity which we are going to describe now.
Activity To Test Whether A Material Is A Conductor Or An Insulator
We take a cell, a torch bulb fitted in a holder and some connecting wires (copper wires) with crocodile clips, and connect them as shown in Figure. A gap is left between the ends of crocodile clips A and B, so no electricity flows in this open circuit and hence the bulb does not light up in this case.
The arrangement shown in Figure is known as ‘conduction tester’. It is used to find out whether an object (or material) conducts electricity or not. The object (or material) to be tested is connected in the gap between crocodile clips A and B (see Figure). If the object makes the bulb light up (or glow), it will be a conductor of electricity but if the object does not make the bulb light up, it will be a non-conductor of electricity or insulator. This will become more clear from the following activities.
(i) Let us insert a paper clip made of steel in the gap between the free ends of the crocodile clips A and B to complete the circuit [as shown in Figure (a)]. We will see that the bulb lights up at once. This means that the paper clip made of steel allows the electricity (or electric current) to pass through it so that the current starts flowing in the circuit (including the bulb). Since electric current passes through the bulb, it lights up (or glows). This observation (glowing of bulb) shows that steel is a conductor of electricity.
If we remove the steel paper clip and connect a pencil (sharpened at both ends) in the gap between the crocodile clips A and B, we will find that the bulb lights up again. This shows that graphite (the black substance present inside the pencil) is also a conductor of electricity.
Please note that the connecting wires used in this experiment are made of copper. Since these copper wires allow the electric current to pass through them, therefore, copper is also a conductor of electricity.
(ii) We now insert a rubber eraser in the gap between the free ends of crocodile clips A and B [as shown in Figure (b)]. We will see that the bulb does not light up at all. This means that the rubber eraser does not allow electricity (or electric current) to pass through it so that no current flows in the circuit (including the bulb). Since electric current does not pass through the bulb, it does not light up. This observation (not glowing of bulb) shows that rubber is a non-conductor of electricity. In other words, rubber is an insulator.
If we remove the rubber eraser and insert a plastic scale, a matchstick (made of wood), a piece of paper or a piece of cloth in the gap between the two ends of crocodile clips A and B , turn by turn, we will find that even then the bulb does not light up.
This shows that plastic, wood, paper and cloth do not allow electric current to pass through them. So, plastic, wood, paper and cloth are all non-conductors of electricity. In other words, plastic, wood, paper and cloth are all insulators. In Figure, there is only air in the gap between the two ends of crocodile clips A and B.
Since the bulb does not light up when there is only air in the gap between the two ends of wires in a circuit, it means that air is a non-conductor of electricity. In other words, air is an insulator.
Importance of Conductors and Insulators
Conductors and insulators are equally important for us because they are both useful in their own ways. Conductors are used to carry electricity (or electric current). For example, electricity is carried in our homes by copper wires (or aluminium wires) because copper (and aluminum) are conductors of electricity.
The electricity used in our homes can be dangerous. A person will get an electric shock if he touches a bare wire carrying electricity (or electric current). It can even kill a person. Insulators are used for safety. Insulators protect us from getting electric shocks. Insulators allow us to handle current-carrying wires, switches, plugs, sockets, and other electrical appliances safely (see Figure).
For example, the electric wires are covered with insulators like plastic or rubber. Being an insulator, plastic (or rubber) covering does not conduct electricity flowing through the wire into our body when we touch it. So, if we happen to touch a current-carrying wire covered properly with plastic (or rubber) insulation, we will not get an electric shock.
Thus, the plastic (or rubber) covering on the wires protects us from the electricity that is flowing through the wires. In other words, the plastic insulation makes the electric wires safe to touch. Just like electric wires, electric switches, and electric plugs, etc., are also covered with insulator material like plastic to protect us from the electricity passing through them (see Figure).
The knowledge about the conducting or insulating properties of various materials is made use of in choosing materials for making electrical components and appliances like electric wires, electric switches, electric plugs, electric sockets, electric iron, toaster and ovens, etc.
(i) Those parts of an electrical component or appliance through which electric current has to pass, are made of conductors like metals or metal alloys.
(ii) Those parts of an electrical component or appliance which are touched by us while handling, are made of insulators like plastic, rubber or wood, etc. (so that current may not pass through them). The electric wires are made of metals like copper and aluminium because they are conductors but the outer covering of electric wires is made of plastic (or rubber) because it is an insulator (see Figure).
Similarly, the pins of an electric plug are made of metal which is a conductor but the outer case is made of plastic which is an insulator (see Figure). The inner parts of electric switches and electric sockets are made of metal (conductor) but their outer case is made of plastic (insulator). The heating element of an electric iron is made of a metal alloy (which is a conductor) but this heating element is enclosed in a sheet of mica which is an insulator.
The handle and top part of an electric iron (which we touch) are made of plastic which is also an insulator. Rubber, plastics and ceramics are often used to protect us from the dangers of electricity because they are good insulators. For example, electricians wear rubber hand gloves while handling naked electric wires because rubber is a good insulator and protects them from electric shocks (see Figure).
The handles of tools like screwdrivers and pliers used by electricians for repair work usually have plastic or rubber covers on them. This is because plastic and rubber are insulators which protect the electrician from electric shocks when he is handling current-carrying electrical appliances.
It is advisable to wear rubber-soled shoes or rubber chappals while operating electrical appliances. This is because rubber is an insulator which will protect us from electric shocks in case there is a leakage of electric current from the appliance.