Electricity in Our Lives

• P – Point → In the above paragraph, I point out to the theory of: The historical evolution and scientific development of electricity through chronological discoveries.

• E – Evidence → The evidence that supports the theory is: William Gilbert first coined the term 'electricus'. Later, Benjamin Franklin explained how electric charges work. Alessandro Volta and Luigi Galvani discovered electric currents. Finally, Thomas Edison and Nikola Tesla created modern power systems to bring electricity into our homes.

• E – Explanation → Now I explain my point: Each scientist built upon previous findings. They transformed static electricity concepts into functional currents. This progressive understanding enabled the creation of safe commercial power grids.

• L – Link → I link my knowledge of electricity to: The practical use of electricity in our daily lives and the modern urgency to conserve energy for a sustainable future.

1. Static charge had accumulated on Sara's body due to friction. When she touched the metal doorknob, which is a conductor, the accumulated charge suddenly discharged through the metal, producing a small electric shock. This demonstrates electrostatic discharge.

2. An electroscope is used to detect electric charge. When a charged balloon is brought near the metal disc of a neutral gold-leaf electroscope, charges in the electroscope redistribute by induction. The two leaves acquire like charges and diverge. Thus, the divergence of the leaves shows that the balloon is charged.

3. Lightning occurs when opposite static charges build up in clouds and on the Earth. When these charges suddenly move through the air, a bright flash of lightning is produced.

1. Thunder
   Reason — Lightning, electroscope and comb are all associated with electric charges, whereas thunder is only a sound produced by the rapid expansion of heated air.
2. Electric power
   Reason — Fuse, MCB and insulator are all related to electrical safety, whereas electric power is a physical quantity (the electrical energy consumed per unit time).
3. Lightning rod
   Reason — Charging by friction, conduction and induction are all methods of charging an object, whereas a lightning rod is a device used to protect tall buildings from lightning.
4. Plastic
   Reason — Copper, aluminium and iron are conductors of electricity, whereas plastic is an insulator.
5. Electric motor
   Reason — Static electricity, electric charges and conservation of charges are all concepts of electrostatics, whereas an electric motor is a device.

1. Two kinds — static electricity and current electricity.
2. Electrostatic force.
3. Valence electrons are the electrons present in the outermost orbit of an atom.
4. The charge on the body is negative when the number of protons is less than the number of electrons.
5. Power plants, cells and batteries.

1. Current electricity is the flow of electric charge through a conductor.
2. Electrons revolve around the nucleus along circular paths in orbits.
3. Conductors are the materials that allow electrons to flow through them.
4. A/An electroscope is a device that is used for detection of small amount of charge on a body.
5. Lightning is a high energy electric discharge that takes place in the atmosphere.

1. False
   Corrected Statement — The neutral wire completes the circuit by returning the electricity to the source (transformer) after it has passed through the appliance.
2. False
   Corrected Statement — Batteries which are designed to be recharged and used a number of times are secondary batteries.
3. False
   Corrected Statement — A short circuit occurs when the live wire touches the neutral wire, providing an alternate path for the current to flow through.
4. True
5. True

1. Fuse wire has a higher resistance and in case of overloading its temperature rises much faster than the connecting copper wire.
2. The earth wire has no current flowing through it. One end of the earth wire is connected to the appliance and the other end is grounded.
3. Induction is a method of charging an uncharged conductor just by bringing a charged body in close vicinity but not making any physical contact with the uncharged body.
4. Insulators are the materials that do not allow electrons to flow through them.
5. Static electricity is caused by the build-up of charges on the surface of an object.

Carpets are usually made of nylon or wool, which give away their electrons and become positively charged. As we walk, our feet rub against the carpet, so a large amount of charge builds up and these electrons stay on the surface of our body. When we touch a conductor like a metal doorknob, the electrons flow from our body to the doorknob, and we experience a light electric jerk.

When a balloon is rubbed against hair, free electrons are transferred between the two. The rubber balloon has a greater affinity for free electrons than hair, so it pulls electrons from the hair and becomes negatively charged, leaving the hair positively charged. Since the two acquire equal and opposite (unlike) charges, and unlike charges attract each other, the balloon and the hair attract each other.

In charging by conduction, the charged object is brought in direct contact with the neutral object, and some charge is transferred between them. For example, when a negatively charged rod touches a neutral sphere, electrons flow from the rod to the sphere and the sphere also becomes negatively charged. Thus, the neutral object acquires the same nature of charge as the object used for charging.

In houses, the wiring is done in such a way that all the devices are connected in parallel. In a parallel connection, each appliance has its own independent path for current. So, switching off the lights and fans of one room does not turn off or disturb the other appliances in the house.

The earth wire is a safety wire. If the insulation of an appliance gets damaged and the bare live wire touches its metal casing, the earth wire carries the leakage current safely into the earth. As a result, a person touching the appliance does not receive a severe electric shock. That is why such appliances are provided with an earth wire.

Current electricity is the flow of electric charge through a conductor in a closed circuit.

The characteristics of a fuse are:

• It is made of a thin wire of an alloy with a low melting point.
• It has high resistance compared to ordinary wires.
• It melts and breaks the circuit when excess current flows.
• It protects electrical appliances and wiring from overloading and short-circuiting.

Lightning is a high energy electric discharge that takes place in the atmosphere. It is caused by the accumulation of static charges in the clouds. When a large amount of charge accumulates, the insulating property of the air breaks down, and an electric discharge takes place between two oppositely charged clouds or between a charged cloud and the ground.

Lightning conductors are fixed on the roofs of tall buildings to protect them from lightning. They provide a safe, low-resistance path for the electric charge to flow into the Earth, preventing damage to the building and reducing the risk of fire.

We can conserve electricity by:

• Using energy efficient appliances like LED bulbs and compact fluorescent lamps (CFLs).
• Turning off appliances, lights and fans when they are not in use.
• Closing doors when the air conditioner is on.
• Switching off devices at the plug point and not just by the remote.

Aim: To study the nature of charges.

Materials required: Two ebonite rods, fur, two glass rods, silk cloth and thread.

Procedure and observation:

• Rub a glass rod with silk cloth and suspend it freely with a thread. Rub another glass rod with silk and bring it near. The two glass rods repel each other.
• Rub two ebonite rods with fur and bring them near each other. The two ebonite rods also repel each other.
• Now bring the silk-rubbed glass rod near the suspended fur-rubbed ebonite rod. The two rods attract each other.

Conclusion: There are two types of charges — positive and negative. Like charges repel each other, while unlike charges attract each other.

This statement is the law of conservation of charge. Before rubbing, a glass rod and a silk cloth are both neutral and neither attract nor repel each other. When the glass rod is rubbed with the silk cloth, some electrons (negative charge) are transferred from the glass rod to the silk. The glass rod loses electrons and becomes positively charged, while the silk gains the same number of electrons and develops an equal negative charge.

Similarly, when an ebonite rod is rubbed with fur, the ebonite rod gains electrons and becomes negatively charged, while the fur loses an equal number of electrons and becomes positively charged. Thus, the two bodies always acquire equal and opposite charges by rubbing. The charge is not created or destroyed; it is only transferred from one body to another. This is called the law of conservation of charge.

An electroscope is a device that is used for the detection of a small amount of charge on a body. It also gives information about the nature of the charge, that is, whether it is positive or negative.

The two most widely used electroscopes are:

• Pith-ball electroscope: It consists of a pith-ball suspended with a silk thread from an insulating stand. The body to be tested is brought close to the pith-ball without touching it. If the ball shows any movement, the body is charged; if the ball remains stationary, the body is uncharged.

• Gold-leaf electroscope: It consists of a glass bell jar fitted with an insulated plug, through which a brass rod passes. The upper end of the rod carries a brass disc, and the lower end inside the jar carries two thin metallic leaves. When a charged body touches the brass disc, the charge passes to the leaves, which acquire the same charge and diverge due to repulsion.

The safety measures to be followed during lightning are:

Out of the house:

• If you are in an open ground with no shelter, squat down with your feet together.
• Do not go on the terrace or roof of any tall building.
• Stay away from water bodies such as rivers, ponds, lakes and swimming pools.
• Do not carry an umbrella in an open ground and do not stand under a tree.
• Take shelter inside a building or a parked vehicle with all its doors and windows closed, without touching the metallic frame of the vehicle.

Inside the house:

• Stay away from doors and windows and keep them shut.
• Do not take a shower or make contact with running water or a metallic tap.
• Do not operate electrical appliances like televisions and computers.
• Do not use a corded telephone.

1. During a thunderstorm, the lightning conductor protects the house by safely discharging the electric charges from the cloud into the ground. This prevents the building from being damaged by lightning.

2. When Naman rubbed the balloon on his hair, the balloon became charged by friction. When he brought the charged balloon close to Preet's arm, it exerted an electrostatic force on the hair, so the hair was attracted towards the balloon and stood up.

3. During a thunderstorm, lightning can cause a sudden surge of high voltage in the wiring, which can damage the appliances. Unplugging the appliances protects them from this damage and also helps save electricity.

4. A fuse is the weakest part of the circuit. In case of overloading or a short circuit, excess current flows through it, so the fuse wire gets heated and melts. This breaks the circuit and stops the current, preventing fire and damage to the appliances.

5. Conductor — the lightning conductor (made of metal). Insulator — the rubber balloon.

1. Static electricity is the electricity caused by the build-up of charges on the surface of an object. The word 'static' is used because the charges are at rest.

2. Static electricity is the build-up of charges that are at rest on the surface of an object, whereas current electricity is the flow of electric charge through a conductor.

3. According to the passage, static electricity was first described in ancient times by the Greek philosopher Thales (around 600 BC), who observed the attractive power of amber when rubbed with fur.

4. In 1836, Faraday demonstrated that the measurement of a charge depends on the observer's electrical state, and he developed the Faraday cage to measure static electricity quantitatively for the first time.

When the plastic pen is rubbed against the dry sweater, electrons are transferred between the two and the pen becomes charged by friction. The charged pen now sets up an electrostatic force around it. When it is brought near the tiny paper bits, this electrostatic force attracts them, so the small paper bits jump towards the pen.

During a thunderstorm, lightning may strike the power lines and send a sudden surge of very high voltage and current into the household wiring. If appliances like a TV or refrigerator are switched on, this surge can flow through them and damage them, or even cause an electric shock or fire. To avoid this risk, electricians advise not to use such appliances during a thunderstorm.

Power of the iron = 1000 W = 1 kW

Total time of usage = 2 h × 10 = 20 h

Energy consumed = Power × Time = 1 kW × 20 h = 20 kWh = 20 units

Total cost = Total units × Cost of each unit = 20 × ₹6 = ₹120

∴ The total electricity bill is ₹120.

Power of the geyser, P = 3000 W

Voltage, V = 220 V

Current drawn by the geyser, $I = \frac{P}{V} = \frac{3000}{220} = 13.64$ A (approximately)

The geyser draws a current of about 13.64 A, which is much more than the fuse rating of 5 A. So the current exceeded the safety limit and the fuse melted.

∴ No, the fuse was not appropriate. A fuse of a higher rating (more than 13.64 A, for example 15 A) should have been used for the geyser.

Materials required: A balloon (or a plastic comb), small bits of paper and a woollen cloth (or dry hair).

Steps:

• Inflate a balloon and tie its end (or take a dry plastic comb).
• Rub the balloon with the woollen cloth (or rub the comb through dry hair) for about 20–30 seconds.
• Bring the rubbed balloon or comb close to the small bits of paper kept on a table.

Expected observation: The small paper bits get attracted to the balloon (or comb) and may stick to it. This happens because the balloon or comb acquires a static charge by friction and exerts an electrostatic force on the paper bits. This shows the presence of static electricity.

Three safety rules for the home during a thunderstorm:

• Stay indoors and keep all doors and windows shut.
• Do not operate or use electrical appliances like the TV and computer, and avoid using a corded telephone.
• Do not touch running water, metal taps or any conductive (metal) objects.

Poster:

1. Static electricity is generated when two objects are rubbed together.

2. Electric charges arise due to an imbalance of protons and electrons in a body. There are two kinds of charges — positive charge (when the number of protons is more than the number of electrons) and negative charge (when the number of electrons is more than the number of protons).

3. During rubbing, the electric charge is not created; it is only transferred. Electrons are transferred from one body to the other, so the two bodies acquire equal and opposite charges.

4. The law of conservation of charge states that charge can neither be created nor destroyed; it can only be transferred from one body to another.

5. During storms, the air around becomes charged and the strands of hair acquire the same (like) charge. Since like charges repel each other, the hair strands push away from one another and stand up.

1. Conductors are materials that allow electrons (electric charge) to flow through them, as they have a large number of free electrons, for example, metals. Insulators are materials that do not allow electrons to flow through them, as they have very few free electrons, for example, plastic and wood.

2. Conductors allow electric charge to flow freely. All metals, such as copper, aluminium and iron, are good conductors.

3. The purpose of an electroscope is to detect a small amount of charge on a body and to find the nature of the charge, that is, whether it is positive or negative.

4. To 'charge' an object means to create an imbalance of charges on it (an excess or deficiency of electrons). An object can be charged by friction, conduction or induction.

5. A charged rod has an electrostatic force around it. It repels objects carrying like charges and attracts objects carrying unlike charges (or light uncharged objects), because like charges repel and unlike charges attract each other.

1. Electrical power is the electrical energy consumed per unit time by an electrical appliance. It is related to energy by the formula Power = $\text P = \frac{\text{Electrical energy}}{\text{Time}}$, that is, $\text P = \frac{\text E}{\text t}$. Its SI unit is the watt (W).

2. Overloading is the situation when many appliances are connected to a single socket, so that the circuit draws a large amount of current from the mains. This causes excessive heating of the connecting wires and the circuit, and can lead to a short circuit.

3. A fuse is the weakest part of the circuit. When excess current flows through it due to overloading or a short circuit, the fuse wire gets hot and melts. This breaks the circuit and stops the flow of current, protecting us from fire and damage.

4. In earthing, the metallic body of the appliance is connected to a thick copper wire whose other end is buried deep in the earth. If the live wire touches the metal casing, the leakage current flows safely into the earth, so the person touching the appliance does not get a severe electric shock.

5. When the circuit is overloaded, the excess current causes the fuse to melt (or the circuit breaker to trip), which breaks the circuit. As the circuit is broken, no current flows, so the appliances stop working.

1. Conservation of electricity means using electricity carefully and avoiding its wastage, so that we do not run short of it.

2. We can reduce electrical energy use by using energy efficient bulbs like LEDs and CFLs, turning off lights, fans and appliances when not in use, closing doors when the air conditioner is on, switching off computer monitors when leaving the room, and switching off devices at the plug point.

3. It is important to follow electrical safety rules because electricity can be dangerous if not used safely. Following these rules helps prevent electric shocks, electrocution, short circuits, overloading and fires.

4. Every home should have safety components such as fuses, miniature circuit breakers (MCBs) and earthing (earth wire) in its electrical setup.

5. Conserving electricity reduces the demand on power plants, which saves fuel and natural resources and reduces pollution, benefiting the environment. Using less electricity also reduces overloading and the chance of electrical accidents, improving our safety.

1. The origin of electric charges is due to transfer of electrons between bodies.
2. A device used to detect the presence of charge on a body is called an electroscope.
3. The SI unit of electrical energy is the joule, while in households it is measured in kilowatt-hour (kWh).
4. One kilowatt-hour (kWh) is equal to 3.6 × 10⁶ joules.
5. Earthing is the process of connecting electrical appliances to the ground to prevent electric shocks.

1. False
   Corrected Statement — Static electricity is produced due to the build-up of charges on the surface of an object.
2. True
3. True
4. True
5. False
   Corrected Statement — Earthing prevents a person from getting a severe electric shock during leakage of current in an appliance.

Two uses of an electroscope are:

• It is used to detect whether a body is charged or uncharged.
• It is used to find the nature of the charge (positive or negative) on a body.

Some safety measures to be taken during lightning are:

• Stay indoors and keep all doors and windows shut.
• Do not operate electrical appliances and do not use a corded telephone.
• Avoid water bodies, running water and metallic taps.
• Do not stand under a tree or remain in an open ground; instead take shelter inside a building or a closed vehicle.

One kilowatt-hour (kWh) is the electrical energy consumed when an appliance of power one kilowatt is used for one hour. It is the commercial unit of electricity and is also known as one unit.

It is related to joules as: 1 kWh = 3.6 × 10⁶ J.

A neutral body can be charged by the following three methods:

• Charging by friction: When two neutral bodies are rubbed together, free electrons are transferred from one body to the other, so they acquire equal and opposite charges. For example, when a balloon is rubbed against hair, the balloon becomes negatively charged and the hair becomes positively charged.

• Charging by conduction: When a charged body is brought in contact with a neutral conductor, some charge is transferred to it, and the neutral body acquires the same nature of charge. For example, when a negatively charged rod is touched to a neutral metal sphere, the sphere also becomes negatively charged.

• Charging by induction: When a charged body is brought close to (but does not touch) a neutral conductor, the charges in the conductor separate. For example, if a negatively charged rod is brought near a neutral conducting sphere, electrons in the sphere are repelled to the far side, leaving the near side positively charged. While the rod is still held near the sphere, the sphere is earthed so that excess electrons flow to the ground. The earth connection is removed first and then the charged rod is taken away. The sphere is left with a positive charge, opposite in nature to the charge on the rod.

Construction: The gold-leaf electroscope was developed by Abraham Bennet. It consists of a glass bell jar fitted with an insulated plug made of cork at its mouth. A thin brass rod passes through the cork into the jar. The upper end of the rod, which lies outside the jar, carries a small brass disc, while the lower end inside the jar carries two thin metallic leaves hanging parallel to each other. The whole arrangement rests on an insulated base.

Working: When a charged body is brought in contact with the brass disc, charge passes through the brass rod to the two metallic leaves. Since both leaves acquire the same kind of charge, they repel each other and diverge. Thus, the electroscope detects the presence of charge, and the amount of divergence gives a rough qualitative idea of the amount of charge. To identify the nature of an unknown charge, the electroscope is first given a known charge. If the leaves diverge further when the test body is brought into contact with the disc, the test body has the same kind of charge; if the leaves come closer or collapse, the test body has the opposite kind of charge.

Household wiring is protected using the following safety components:

• Fuse: A fuse is the weakest part of the circuit and is placed in the live wire in series. In case of overloading, a short circuit or voltage fluctuation, excess current flows and the fuse wire melts, breaking the circuit and stopping the current.
• MCB (Miniature Circuit Breaker): An MCB is a switch that automatically turns off when the current in the circuit exceeds the safety limit. It is more reliable than a fuse, as it can simply be switched on again to restore the circuit and does not need to be replaced.
• Earthing: In earthing, the metal casing of an appliance is connected to a thick copper wire buried deep in the earth. If the live wire touches the metal casing, the leakage current flows safely into the earth, protecting the person from a severe electric shock.

Together, fuses, MCBs and earthing protect the wiring, the appliances and the people from electrical hazards.

Power of the geyser = 2 kW

Time of usage = 3 h

Energy consumed = Power × Time = 2 kW × 3 h = 6 kWh = 6 units

Cost = Total units × Cost of each unit

= 6 × ₹6

= ₹36

∴ The energy consumed is 6 kWh and its cost is ₹36.

Importance of conserving electricity: The generation and transmission of electricity is an expensive affair, and it also uses up natural resources. If we keep wasting electricity, a time might come when we would not get enough of it. Therefore, it is very important that everyone learns to conserve electricity, as it saves money and resources, protects the environment and reduces the risk of electrical accidents.

Five practical ways to save electricity:

• Use energy efficient bulbs like LED bulbs and CFLs and energy efficient appliances.
• Turn off the lights, fans and appliances when they are not in use.
• Close the doors when going out of the room while the air conditioner is on.
• Make sure that computer monitors are turned off when leaving the computer room.
• Switch off devices at the plug point and not just by the remote.