Electricity: Circuits And Their Components

Hello students, welcome to today's science lesson. I am so happy to be here with you to learn about one of the most important topics in science — electricity. Today we are going to study Chapter 3: Electricity: Circuits and their Components. This is a fascinating chapter that will help you understand how electricity works in your daily life, from the torchlight you use at home to the big dams that generate power for entire cities. So let's begin our journey into the world of electricity.

So students, let me start with a story. There was a student named Nihal who was very excited about his school trip to the Bhakra Nangal Dam. Have you heard of this dam? It is one of the largest dams in Asia, built on the Sutlej river in Punjab and Himachal Pradesh. The students were going to visit the hydroelectric power house where the force of falling water is used to generate electricity. They were also looking forward to a free 13 kilometre train ride from Nangal in Punjab to Bhakra in Himachal Pradesh, along the beautiful Sutlej river and through the Shivalik hills. That must be a wonderful experience, isn't it?

Before the trip, Nihal and his classmates were given a group assignment to prepare a presentation on the uses of electricity. They began by looking around their houses, then their school, followed by their neighbourhood, their city, and finally they searched the internet. To their astonishment, their list kept growing and growing. They decided to organise the uses under different headings.

Now students, I want you to think about this along with Nihal. Can you name some uses of electricity for cooking? We have electric kettle, mixer grinder, toaster, oven, microwave. Can you add more? What about a pressure cooker with an electric heater, or an electric stove, or a rice cooker? Yes, there are many more.

For lighting, we have homes, offices, streets, markets, factories. What else? Perhaps street lights, searchlights, decorative lights during festivals, flashlights in mobile phones, and so on.

For transportation, we have train, bus, car, scooter, lift, escalator. Think about electric trains like the metro, electric cars like Tesla, electric bikes, and even electric airplanes being developed nowadays.

For heating and cooling, we have fan, room heater, immersion rod, geyser, refrigerator, air conditioner. What else can you think of? Perhaps a cooler, a desert cooler, an electric iron, a water dispenser, a烤箱 (oven) for baking.

For entertainment, we have television, radio. What else? Video games, music systems, home theatre, streaming devices like Firestick, projectors.

For communication, we have mobile phone, internet. What else? Landline telephones, walkie-talkies, satellite phones, radio communication.

For others, we have water pump, crane, computer. What else? Washing machines, dishwashers, printers, scanners, electric doorbells, security cameras.

Now, can you help Nihal by adding some more uses to his lists? Also, suggest some other ways of grouping the uses of electricity. For example, we could group them by where electricity is used — at home, at school, in hospitals, in factories, in transportation. Or we could group them by the amount of power they need — low power devices like remote controls, medium power devices like fans, high power devices like air conditioners.

Now students, we use electricity all the time, so let us learn something more about electricity. You have learnt earlier that electricity is generated in multiple ways — by windmills using wind energy, by solar panels capturing the Sun's energy, by falling water as at Bhakra Nangal Dam, and by using natural gas or coal. This is discussed in the chapter 'Nature's Treasures' in your Grade 6 Science textbook Curiosity. The electric supply from these sources reaches our homes and factories via wires. For example, at home we plug in various devices to the electrical sockets in the wall.

However, to learn about electricity, we will focus on a portable source of electricity that most of us may have used. Let us start with its use in a common device like a torchlight. But before we begin, I must give you a very important caution.

Caution — The danger signs on electric poles and other appliances warn people that electricity can be dangerous if not carefully handled. Never ever perform experiments with power supply at your home or school. Even electricity from portable generators can be dangerous. Use only batteries or cells, like those in torchlights, wall clocks, radios, or remotes, for experiments with electricity. This is very important, students. Always remember this safety rule.

Now let's begin with Section 3.1: A Torchlight.

You might have used a torchlight, also called a torch or a flashlight. It is a very common device that we use when there is no light, like during power cuts or when we go to dark places.

Now let's do Activity 3.1: Let us explore.

Take a torchlight similar to the one shown in the figure in your textbook. Observe it carefully. Do you notice a lamp? And a switch? Yes, every torch has a lamp that produces light and a switch that turns it on and off.

Now, slide its switch and observe. Does the torch lamp glow? Yes, when you slide the switch to the on position, the lamp glows. Now slide the switch back to its original position and observe the torch lamp. The lamp stops glowing. So we can say that in one position of the switch, the torch lamp glows and in the other position the lamp does not glow.

Now, open the torchlight. What do you find inside? Inside the torchlight, you may find two or more electric cells. These cells provide the electricity to make the lamp glow.

Now here is a question for you: Why does the torch lamp glow in one position of its switch? We will answer this question soon, but first we need to understand the components of a torchlight.

Now let's move to Section 3.2: A Simple Electrical Circuit.

To understand how a torch works, let us first find out about its components.

### 3.2.1 Electric cell

Let's do Activity 3.2: Let us observe.

Take an electric cell, turn it around and look at it carefully. Do you notice a positive plus sign and a negative minus sign marked on the electric cell? Yes, you will see these symbols on every cell. Do you also notice that it has a small protruding metal cap on one side and a flat metal disc on the other side? The metal cap is the positive terminal of the electric cell and the metal disc is the negative terminal.

So students, remember that all electric cells have two terminals; one is called positive, written as plus ve, while the other is negative, written as minus ve. The electric cell is a portable source of electrical energy. It converts chemical energy into electrical energy. This is the power source that makes our torchlight work.

### 3.2.2 Battery

Now, in a torch, we generally use more than one cell. Have you ever wondered why? Are those placed in any particular order? Let's find out.

Let's do Activity 3.3: Let us experiment.

Take a torch which uses two cells. Open its cell compartment and take out the cells. Now put the cells back in a different order. Also, try reversing the direction of one cell. Then, slide the switch and check whether the lamp glows in each case. Check the order in which the cells were placed in the torch when the lamp glows.

What do you observe? The lamp glows when the cells are placed in a particular order. Notice how the terminals of the two cells are connected. The positive terminal of one cell is connected to the negative terminal of the next cell. Such a combination of two or more cells is called a battery.

So students, a battery is not just a single cell — it is a combination of two or more cells connected together. When we connect cells this way, with the positive terminal of one cell touching the negative terminal of the next, we call it connecting them in series.

Now, why do we use more than one cell in a torch? Connecting more than one cell provides energy to the circuit for a longer time and or more energy. With more cells, the torch stays bright for a longer period and the light may be brighter too.

Here is a fascinating fact for you: The term battery is also used for a single cell. We use the term battery even for the single cell that powers our mobile phones. Technically, a mobile phone battery is actually a battery of many cells connected together, but we commonly call it a battery even when it is a single unit.

### 3.2.3 Electric lamp

Now let's learn about the electric lamp. There are two main types of lamps used in torchlights: incandescent lamps and LED lamps.

#### Incandescent Lamp

Let's do Activity 3.4: Let us observe.

For this activity, you will require a torchlight with an incandescent lamp or light bulb. Many old torchlights still use such lamps. With your teacher's help, confirm that your torchlight uses an incandescent lamp.

Take the torch and examine its lamp. What do you see? Do you notice a thin wire fixed in the middle of the glass bulb? Yes, there is a very thin wire inside.

Now, switch on the torch. Which part of the lamp glows? The thin wire inside the glass bulb of the lamp glows. This glowing thin wire is called the filament of the lamp. The word filament comes from the Latin word 'filum' meaning thread. It is called filament because it is a very thin thread-like wire.

Now, take out the lamp with the help of your teacher and inspect it from all sides. How is the filament fixed? The filament is attached to two thicker wires that support it. One thick wire connects to the metal case at the lamp's base, while the other connects to the metal tip at the centre of the base. These form the two terminals of the lamp, and are fixed in a way that they do not touch each other. In such incandescent lamps, the filament gets hot and glows to produce light. This is why they are called incandescent lamps — the word incandescent means glowing with intense heat.

However, some of you might say, "However, my torch has a different kind of lamp. In fact, it cannot be taken out of the torch as it is fixed in it." That is absolutely fine. Many modern torches have fixed lamps.

#### LED Lamp

Many torches in use today have a Light Emitting Diode, LED, lamp, instead of an incandescent lamp.

Let's do Activity 3.5: Let us observe.

Take an LED of any colour and observe. Do you see any filament inside it? No, there is no filament inside an LED. That is one major difference between incandescent lamps and LEDs.

Notice the length of two wires attached to the LED. Do you find one of those longer than the other? Yes, one wire is longer than the other. Unlike incandescent lamps, LEDs do not have filaments. They also have two terminals, but one is positive attached to a longer wire and the other is negative the shorter wire. A torch may use one or more LEDs, sometimes of different shapes, in its lamp.

So students, remember this important difference: Incandescent lamps have filaments that glow when heated, while LEDs do not have filaments. LEDs are semiconductor devices that emit light when electric current passes through them.

Now, after having learnt about the electric cell, battery, and electric lamps, we are now ready to make the torch lamp glow using an electric cell or battery.

### 3.2.4 Making an electric lamp glow using an electric cell or battery

Let's do Activity 3.6: Let us construct.

Take an electric cell, an incandescent lamp used in a torch, a cell holder, a lamp holder, and four lengths of electric wire.

First, remove about 1 cm of the plastic covering from both ends of each wire to expose the metal. This is important because the metal part needs to touch the terminals to conduct electricity.

Now, attach two wires to the two ends of the cell holder. Insert the cell in the holder such that its negative terminal is towards the spring side of the holder. The spring helps to keep the cell in place and makes good contact. In case a cell holder is not available, fix the two wires to the cell using electrical tape.

Now, attach two wires to the screws of the lamp holder. Fix the lamp in the holder by turning it around in the holder. In case a lamp holder is not available, use electrical tape to attach two wires to the two ends of the lamp.

Now, we are ready to connect the cell to the lamp to make it glow.

We will conduct this activity in two parts — prediction and observation. Some of the ways in which the lamp and the cell can be connected are shown in Table 3.1 in your textbook.

Now, predict for each arrangement if the lamp will glow or not and write your prediction in Table 3.1. Then, connect the lamp and the cell, and observe if the lamp glows or not. Note down your observation in Table 3.1. Also, for the lamps which glow, colour their glass bulbs yellow.

Now, what do we observe? The lamp glows in some arrangements and does not glow in others. Specifically, the lamp glows in the arrangements where one terminal of the lamp is connected to one terminal of the electric cell and the other terminal of the lamp is connected to the other terminal of the cell. The lamp does not glow in the arrangements where the connections are not complete.

Now, carefully look at the arrangements in which the lamp glows. Compare these with those in which the lamp does not glow. Can you find the reason for the difference? The reason is that the lamp glows only when there is a complete path for the electric current to flow from one terminal of the cell to the other through the lamp.

### 3.2.5 An electrical circuit

Now let's understand what an electrical circuit is.

The lamp glows when one terminal of the lamp is connected to one terminal of the electric cell and the other terminal of the lamp to the other terminal of the cell. This setup forms an electrical circuit, which provides a complete path for electric current to flow through the lamp. The lamp glows only when current passes through the circuit.

So students, an electrical circuit is a complete path through which electric current can flow. It includes a source of electricity like a cell or battery, and devices like lamps that use the electricity, all connected by wires.

The direction of electric current in an electrical circuit is taken to be from the positive to the negative terminal of the electric cell. This is a convention that scientists have agreed upon. When the terminals of the lamp are connected with those of the electric cell by wires, the current passes through the filament of the incandescent lamp and makes it glow. With an incandescent lamp, it does not matter which of its terminals connects to the positive or negative terminal of the cell. The lamp will glow as long as the circuit is complete and current flows through the filament.

Here is a fascinating fact: Sometimes, an incandescent lamp does not glow even when connected to a cell. We say the lamp has fused, usually due to a broken filament. A broken filament stops the flow of current, preventing the lamp from glowing. This happens when the filament breaks due to age or sudden shock. That is why sometimes torchlights stop working even when the cells are new — the filament might have fused or broken.

Now let us try to make an LED glow. This is a bit different from making an incandescent lamp glow.

Let's do Activity 3.7: Let us experiment.

Take two electric cells, an LED of any colour, a cell holder that can fit two cells, and two lengths of electric wire. Remove about 1 cm of the plastic covering from both ends of each wire to expose the metal.

Connect the two wires to the cell holder. Insert two cells in the holder, taking care that for each cell, its negative terminal is towards the spring side of the holder, and the battery is ready to use.

Now, how will you decide which is the positive terminal of this battery? The terminal of the holder which is connected to the positive terminal of one cell is positive and the one connected to the negative terminal of the other cell is the negative terminal.

Now, connect the free end of the battery positive terminal wire to the longer wire of LED, and the free end of the second wire to the shorter wire of LED. Does the LED glow? Yes, it should glow.

Now repeat the above step but interchange the wires connected to the LED. Does the LED glow again? No, it does not glow.

You would have observed that the LED glows in the first case and does not glow in the other. It is because the current can pass through the LED in one direction only. The current passes through the LED only when the positive terminal, which is the longer wire of the LED, is connected to the positive terminal of the battery, and the negative terminal, which is the shorter wire of the LED, is connected to the negative terminal of the battery. When current passes through the LED, it glows. Always take care to connect an LED correctly in a circuit to make it glow.

So students, remember this important difference between incandescent lamps and LEDs. Incandescent lamps will glow regardless of which way you connect them to the cell, but LEDs will only glow when connected in the correct direction. This is because LEDs are diodes, and diodes allow current to flow in only one direction.

Now, let me add a deeper dive here. Sometimes you may come across a device in which the cells are placed side by side. Then, how are the terminals of the cells connected? If you carefully look inside the battery compartment, you will usually see a thick wire or metal strip connecting the positive terminal of one cell to the negative terminal of the next. To help with proper placement, plus and minus symbols are typically printed inside the battery compartment. This ensures that we place the cells in the correct direction.

### 3.2.6 Electric switch

Now, let's learn about the electric switch. How does a switch turn on or off the torchlight? Let's find out.

Let us first make a simple switch on our own.

Let's do Activity 3.8: Let us construct.

Collect two drawing pins, a safety pin or a paper clip, two wires, and a small piece of cardboard. Insert a drawing pin through the ring of the safety pin and fix it to the cardboard piece, ensuring that the safety pin can rotate freely. Fix the second drawing pin to the cardboard piece so the free end of the safety pin can touch it. Connect a wire to each drawing pin — our switch is ready!

Now let's test our switch.

Let's do Activity 3.9: Let us test.

Connect the electric cell, lamp, and switch as shown in the figure. Does the lamp glow? No, it does not glow because the switch is open and the circuit is broken.

Now, rotate the free end of the safety pin till it touches the other drawing pin. Does the lamp glow now? Yes, it does!

When the safety pin touches both drawing pins, it closes the gap and completes the path, and allows the current to flow. We call this the ON position where the circuit is closed and current flows from the cell's positive to negative terminal making the lamp glow. When the safety pin does not touch the second drawing pin, the gap in the circuit prevents current flow, and the lamp does not glow. In this OFF position, we say that the circuit is open.

So students, a switch is a simple device that either completes or breaks a circuit. When the switch is in the ON position, it closes the circuit and allows current to flow. When the switch is in the OFF position, it opens the circuit and stops the current flow. Note that a switch can be placed anywhere in a circuit. The switches used for lights and other devices at home work the same way, though they are designed differently.

Now, let's move to Section 3.3: Circuit Diagrams.

Can we represent the circuits in a simpler manner? Yes, we can! Instead of drawing complicated pictures of cells, lamps, and wires, we use standard symbols to represent electrical components. This makes it much easier to draw and understand electrical circuits.

The various components of an electrical circuit can be represented by symbols shown in Table 3.2 in your textbook.

Let me describe these symbols to you:

For an electric cell, the symbol is a long line and a short line parallel to each other. The long line represents the positive terminal, while the short line represents the negative terminal.

For a battery, which is a combination of cells, we draw multiple pairs of these lines.

For an electric lamp, the symbol looks like a cross inside a circle. This represents the filament inside the bulb.

For a Light Emitting Diode, the symbol is similar to a diode symbol with two arrows pointing outwards indicating that it emits light.

For a switch in the ON position, the symbol shows the switch closed, meaning the circuit is complete.

For a switch in the OFF position, the symbol shows the switch open, meaning the circuit is broken.

For wire, we use straight lines to show the connections.

In the symbol for an electric cell, the long line represents the positive terminal, while the short line represents the negative terminal.

In the symbol for an LED, the triangle points to the direction in which the current can flow. The two arrows indicate that an LED emits light.

By using symbols to represent electrical components, it is easier to draw and understand electrical circuits. A representation of an electrical circuit using symbols is called its circuit diagram.

Now let's do Activity 3.10: Let us draw.

Using symbols shown in Table 3.2, draw the circuit diagram of an electrical circuit given in the figures in your textbook. Are your circuit diagrams similar to the ones shown in the textbook? They should be!

Here is a deeper dive for you: International organisations, such as the International Electrotechnical Commission, IEC, American National Standards Institute, ANSI, and the Institute of Electrical and Electronics Engineers, IEEE, create standard symbols for electrical and electronic parts. Using the same symbols across the world helps people from different countries and industries understand each other easily. This is why it is important to learn these standard symbols.

Now, let's move to Section 3.4: Electrical Conductors and Insulators.

Why did we use metal wires for making electric circuits? Can we not use some other materials for wires? Also, why are electric wires covered with plastic or rubber?

Let's think about this. Suppose we make wires of materials other than metal and use them for making the electrical circuit. Do you think the electric current will pass through those materials in such a circuit? Let's find out.

Let's do Activity 3.11: Let us identify.

First, connect an electric cell and a lamp while leaving the two ends of wires free as shown in the figure. Touch the two free ends of the wires momentarily. Does the lamp glow? If yes, our tester is ready. We can use this tester to identify the materials through which electric current passes.

Now, collect objects of different materials, such as metal spoons, coins, cork, rubber, glass, keys, pins, plastic scale, wooden block, aluminium foil, candle, sewing needle, cardboard, paper, and pencil lead.

One by one, touch the free ends of the tester's wires to both ends of each object you have collected. Make sure the wires don't touch each other. Does the lamp glow every time? No, it does not.

Now, record your observations in Table 3.3 in your textbook.

Based on the observations you will find that the lamp glows for some materials only. This means that electric current can pass easily through some materials but not through others.

The materials through which electric current can flow easily are called good conductors, or conductors of electricity. The materials through which current cannot pass through are called insulators, or poor conductors of electricity.

From your conclusions, you would have realised that metals are conductors of electricity, and thus, are used for making wires. Metals like copper, aluminium, and iron conduct electricity very well.

Here is a deeper dive: Silver, copper, and gold are the best electrical conductors. However, for making electrical wires, mainly copper is used due to its comparatively lower cost and abundant supply. Different types of electrical wires are used for different uses.

From your observations, you would have also realised that plastic, rubber, and ceramics are electrical insulators. Have you now understood why wires are covered with those materials? Yes, the plastic or rubber covering on wires is an insulator that protects us from getting electric shocks. It prevents the current from flowing through our bodies if we touch the wire.

Conductors and insulators are both important. Electrical wires, switches, connectors of plugs, and sockets are made of conductors. Insulators like rubber, plastics, and ceramics are used to cover wires, plug tops, and switches to protect people from electric shocks.

Now, here is a very important caution: Our body is a conductor of electricity. Electric current passing through our body may cause severe injury or even death. Always handle electrical appliances with care. Never touch switches or plugs with wet hands, or use electrical devices in wet areas, or handle equipment with damaged insulation or broken plugs. This is extremely important, students. Always remember this safety rule.

Here is another deeper dive for you: Have you ever wondered how the electricity from a cell or battery is different from the electricity coming from a wall socket? Electricity from batteries usually powers small devices and is of a type called Direct Current, DC. In contrast, the electricity from power plants that come to the wall socket is known as Alternating Current, AC, and can run larger appliances. We will learn more about these in higher classes.

Now let's review what we have learned so far in "In a Nutshell".

An electric cell is a portable source of electrical energy. It has two terminals; one is called positive, plus ve, while the other is negative, minus ve.

In an incandescent electric lamp, there is a thin wire called the filament, which gets hot and glows to produce light when electric current passes through it.

An LED has two terminals, one is positive attached to a longer wire and the other is negative the shorter wire. Electric current can pass through LED in one direction only. An LED lights up only when its positive terminal, longer wire, connects to the positive terminal of the battery and its negative terminal, shorter wire, connects to the negative terminal of the battery.

A switch is a simple device that either completes or breaks a circuit.

The direction of electric current in a closed electrical circuit is taken to be from the positive to the negative terminal of the electric cell.

A representation of an electrical circuit using symbols is called its circuit diagram.

Materials through which electric current can flow easily are called good conductors or conductors of electricity.

Materials through which current cannot pass through are called insulators or poor conductors of electricity.

Now let's answer the questions in "Let Us Enhance Our Learning".

Question 1: Choose the incorrect statement.

i) A switch is the source of electric current in a circuit. ii) A switch helps to complete or break the circuit. iii) A switch helps us to use electricity as per our requirement. iv) When the switch is in 'OFF' position, there is an air gap between its terminals.

Now, which one is incorrect? Statement i is incorrect. A switch is not the source of electric current in a circuit. The source of electric current is the electric cell or battery. A switch only helps to complete or break the circuit. So the correct answer is i.

Question 2: Observe the figure. With which material connected between the ends A and B, the lamp will not glow?

This question refers to a figure showing a circuit with a gap between points A and B where we place different materials. Based on what we learned about conductors and insulators, the lamp will not glow when we connect an insulator between A and B, because insulators do not allow electric current to pass through. So if we connect materials like plastic, rubber, wood, glass, or paper between A and B, the lamp will not glow. Only conductors like metal keys, coins, or aluminium foil will allow the lamp to glow.

Question 3: In the figure, if the filament of one of the lamps is broken, will the other glow? Justify your answer.

This question refers to a figure showing two lamps connected in a circuit. If the filament of one of the lamps is broken, that means the circuit is broken at that point. Electric current cannot flow through a broken filament. So the other lamp will not glow because the circuit is incomplete. For current to flow and make any lamp glow, the circuit must be complete throughout. A broken filament creates a gap in the circuit just like an open switch.

Question 4: A student forgot to remove the insulator covering from the connecting wires while making a circuit. If the lamp and the cell are working properly, will the lamp glow?

No, the lamp will not glow. The insulator covering on the wires prevents the metal inside from touching the terminals. Since the plastic covering is an insulator, it does not allow electric current to pass through. So even though the lamp and cell are working properly, the current cannot flow because the wires are still covered with insulation. The student needs to remove the plastic covering from the ends of the wires to expose the metal so that it can conduct electricity.

Question 5: Draw a circuit diagram for a simple torch using symbols for electric components.

To draw a circuit diagram for a simple torch, we need to show an electric cell, a lamp, and a switch in the ON position, all connected by wires. The symbol for the electric cell is a long line and a short line parallel to each other, with the long line representing the positive terminal. The symbol for the lamp is a cross inside a circle. The symbol for a switch in the ON position shows the switch closed. We connect these components in a loop using straight lines for wires. The circuit diagram should show the cell connected to the lamp, and a switch in the circuit to turn the lamp on and off.

Question 6: This question has four parts about two switches and two lamps in a circuit. Let's answer each part.

i) If S2 is in 'ON' position, S1 is in 'OFF' position, which lamp(s) will glow?

Looking at the circuit, if S2 is ON and S1 is OFF, then the circuit through lamp 1 is broken because S1 is open. However, lamp 2 is connected through S2 which is closed, so lamp 2 will glow. Lamp 1 will not glow because its switch is open.

ii) If S2 is in 'OFF' position, S1 is in 'ON' position, which lamp(s) will glow?

If S2 is OFF and S1 is ON, then lamp 1 will glow because S1 is closed, completing its circuit. Lamp 2 will not glow because S2 is open, breaking its circuit.

iii) If S1 and S2 both are in 'ON' position, which lamp(s) will glow?

If both switches are ON, then both circuits are complete, so both lamp 1 and lamp 2 will glow.

iv) If both S1 and S2 are in 'OFF' position, which lamp(s) will glow?

If both switches are OFF, then both circuits are broken, so neither lamp will glow.

Question 7: Vidyut has made the circuit as shown in the figure. Even after closing the circuit, the lamp does not glow. What can be the possible reasons? List as many possible reasons as you can for this faulty operation. What will you do to find out why the lamp did not glow?

There can be several possible reasons why the lamp does not glow even when the circuit is closed:

The cell might be dead or have no charge. The filament of the lamp might be broken or fused. The wires might not be properly connected to the terminals. The wires might still have insulation covering at the ends, preventing contact. The switch might not be properly making contact. There might be a loose connection somewhere in the circuit. The lamp might be an LED connected in the wrong direction. One or more of the wire connections might be broken.

To find out why the lamp does not glow, we can check each component one by one. First, we can try a new cell to see if the cell is dead. Then, we can try a new lamp to see if the lamp is fused. We can check all the wire connections to ensure they are properly attached. We can check the switch to ensure it is making proper contact. If using an LED, we can check if it is connected in the correct direction.

Question 8: In the figure, in which case(s) the lamp/LED will not glow when the switch is closed?

Based on the figure, the LED will not glow when the switch is closed if it is connected in the reverse direction, meaning the positive terminal of the LED is connected to the negative terminal of the battery, and vice versa. LEDs allow current to flow in only one direction, so if connected incorrectly, they will not glow even when the circuit is complete.

Question 9: Suppose the '+' and '-' symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.

There are several methods to identify the terminals of a battery if the symbols are not visible:

We can use a voltmeter or multimeter to measure the voltage. The terminal with higher potential is positive. We can use a known LED or diode. Connect the LED with its longer leg to one terminal and shorter leg to the other. If the LED glows, the terminal connected to the longer leg is positive. We can use a compass. Bring a compass near the battery. The needle will deflect towards the north. The end towards which the north-seeking pole of the needle points is the positive terminal. We can use a piece of paper and salt water. Connect wires to both terminals and place them in salt water. Bubbles will form at the negative terminal. These are just some methods that can be used.

Question 10: You are given six cells marked A, B, C, D, E, and F. Some of these are working and some are not. Design an activity to identify which of them are working.

i) List the items that you require.

We will need: the six cells A, B, C, D, E, and F, a working lamp or LED, some connecting wires, a cell holder or holder for multiple cells, and a record table to note which cell works.

ii) Write the procedure that you will follow.

First, set up a test circuit with a cell holder, a lamp, and wires, leaving the cell compartment empty. This is our tester. Now, take cell A and place it in the holder with the correct polarity, making sure the positive terminal is connected properly. Close the switch or complete the circuit. Observe if the lamp glows. If it glows, cell A is working. If it does not glow, cell A may be dead or weak. Repeat this process for cells B, C, D, E, and F, one at a time. Record your observations in a table. You can also test multiple cells together in series to see if they work as a battery.

iii) With the items, carry out the activity to identify the cells that are working.

After carrying out the procedure, we will identify which cells make the lamp glow. Those cells are working. Cells that do not make the lamp glow are dead or not working.

Question 11: Using an LED that requires two cells in series to glow, Tanya made the circuit as shown in the figure. Will the lamp glow? If not, draw the wires for correct connections.

Looking at the figure, if Tanya has connected the LED in the wrong direction, the LED will not glow. The LED requires two cells in series, but it also needs to be connected with the correct polarity. The longer leg of the LED, which is the positive terminal, must be connected to the positive terminal of the battery, and the shorter leg, which is the negative terminal, must be connected to the negative terminal of the battery. If the LED is connected in reverse, it will not glow. To fix this, we need to reverse the connections to the LED so that the longer wire goes to the positive terminal and the shorter wire goes to the negative terminal.

Now let's look at the Exploratory Projects.

Project 1: Suppose that due to some problem, the power supply is disrupted in your area for two days. List out which actions from your daily life you would not be able to do.

Students, think about this. If there is no electricity for two days, we would not be able to: switch on lights and use electric fans, watch television or use the internet, charge mobile phones and laptops, use refrigerator to preserve food, cook food using electric appliances like induction cooker, microwave, or electric oven, use water pumps to draw water, use washing machines, use air conditioners or room heaters, use electric iron to press clothes, use electric doorbells, use elevators and escalators, charge electric vehicles, use ATM machines, and many more. This shows how much we depend on electricity in our daily lives.

Project 2: Using a solar panel as a source of electrical energy, make a circuit to run a toy fan as shown in the figure.

This is a practical activity where you connect a solar panel to a small toy fan motor. The solar panel converts sunlight into electricity, which then flows through the wires to the fan motor, making the fan spin. This demonstrates how solar energy can be used to generate electricity.

Project 3: Visit an electrical items shop. With the help of the shopkeeper, identify the various types of cells available. For each cell, also find out which device(s) it is used for. Prepare a report.

Students, you can visit a local electrical shop and ask about different types of cells. You will find cylindrical batteries of different sizes like AA, AAA, D, C cells used in torchlights, clocks, remote controls. Button cells used in watches, hearing aids, calculators. Rechargeable batteries like lithium-ion batteries used in mobile phones, laptops, and cameras. Lead-acid batteries used in vehicles and inverters. Make a report listing the types and their uses.

Project 4: Prepare a list of objects in your home under three categories: Objects which are electrical insulators only, objects which are electrical conductors only, and objects which are made of both, whose some parts are insulators and some electrical conductors.

For insulators only: plastic toys, wooden furniture, rubber slippers, glass windows, ceramic cups, cotton clothes.

For conductors only: metal spoons, copper wires, aluminium foil, iron nails, gold jewellery.

For both: a pencil — the wood is an insulator but the graphite lead is a conductor. A cup — the ceramic part is an insulator but if it has a metal handle, that part is a conductor. A wire — the metal inside is a conductor but the plastic covering is an insulator. A switch — the plastic body is an insulator but the metal contacts inside are conductors. A plug — the plastic body is an insulator but the metal pins are conductors.

Now let's read the Science and Society section.

Electric cells or batteries are compact portable sources of electrical energy that make the use of some electrical devices more convenient. These cells and batteries come in various shapes and sizes for different purposes, such as cylindrical batteries for torchlights, clocks, remotes, toys; button cells for watches, hearing aids; rechargeable batteries for mobile phones, laptops, and electric vehicles.

Now students, we have completed the entire chapter. Let me give you a complete summary of everything we have learned today.

In this chapter on Electricity: Circuits and their Components, we started with the story of Nihal and his classmates learning about the many uses of electricity in our daily lives, from cooking and lighting to transportation and communication.

We then learned about the electric cell, which is a portable source of electrical energy with two terminals — positive and negative. We learned that a battery is a combination of two or more cells connected together, usually in series, with the positive terminal of one cell connected to the negative terminal of the next.

We learned about two types of lamps: incandescent lamps, which have a thin filament that glows when heated by electric current, and LEDs, or Light Emitting Diodes, which have no filament and glow when current passes through them in one direction only. LEDs have a longer wire for the positive terminal and a shorter wire for the negative terminal.

We learned that an electrical circuit is a complete path for electric current to flow from the positive terminal to the negative terminal of the power source. The lamp glows only when the circuit is complete and current flows through it.

We learned about the electric switch, which is a device that either completes or breaks a circuit. When the switch is in the ON position, the circuit is closed and current flows. When it is in the OFF position, the circuit is open and current does not flow.

We learned about circuit diagrams, which are representations of electrical circuits using standard symbols. This makes it easier to draw and understand circuits.

We learned about electrical conductors and insulators. Conductors are materials through which electric current can flow easily, like metals. Insulators are materials through which current cannot pass, like plastic, rubber, and glass. We use conductors for making wires and insulators for covering wires to protect us from electric shocks.

We also learned important safety rules: never perform experiments with main electricity, always use batteries or cells for experiments, and never touch switches or plugs with wet hands.

We answered all the questions in the Let Us Enhance Our Learning section, including questions about switches, circuits, conductors and insulators, and troubleshooting electrical problems.

We also explored projects that help us apply what we learned to real-life situations.

This is the end of our lesson on Chapter 3: Electricity: Circuits and their Components. I hope you have understood all the concepts clearly. Remember, electricity is a very useful form of energy, but it can also be dangerous if not handled carefully. Always follow safety rules and handle electrical appliances with care.

Thank you students for listening attentively. Keep learning and keep exploring the wonderful world of science. Goodbye and see you in the next lesson.