NCERT Solutions Class 7 Science Curiosity Chapter 03 Electricity: Circuits and Their Components

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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.
Answer: (i) A switch is the source of electric current in a circuit.
The incorrect statement is the first one. A switch does not create or supply electricity to a circuit. Instead, an electric cell or a battery is the real source of current.
In simple words: The wrong statement is (i). A switch only controls the flow, while a battery actually provides the power.

Exam Tip: Always remember that a switch only turns a circuit on or off; it never creates electricity itself.

Question 2. Observe Fig. 3.16. With which material connected between the ends A and B, the lamp will not glow?
Answer: The bulb will not light up if you put an insulator between points A and B. Insulators are materials that block the path of electricity. Some common examples are plastic, wood, rubber, glass, cork, or paper.
In simple words: If you connect an insulator like plastic or wood, electricity cannot pass through and the bulb stays dark.

Exam Tip: In exams, remember to give easy examples of insulators like plastic and rubber to support your answer.

Question 3. In Fig. 3.17, if the filament of one of the lamps is broken, will the other glow? Justify your answer.

Answer: No, the other bulb will not light up. These two bulbs are linked in a single line, which is a series connection. If the tiny wire inside one bulb breaks, it cuts the only path available for the electricity. Since the loop is broken, the electric current stops moving entirely, and neither bulb will light up.
In simple words: Since the bulbs are connected in a single loop, a break in one bulb stops electricity from reaching the other bulb.

Exam Tip: In a series circuit, any break anywhere in the loop stops the current completely.

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?
Answer: No, the bulb will not light up. The plastic or rubber cover on the wire acts as an insulator. It blocks the metal wire inside from touching the metal parts of the cell or bulb. Without real metal-to-metal contact, the path remains open, and electricity cannot flow through the circuit.
In simple words: The plastic cover on the wire blocks the electricity. The metal wires must touch each other directly for current to flow.

Exam Tip: For a circuit to work, you must strip the insulating ends of the wires to make sure metal touches metal.

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

Answer: A simple torch circuit has key parts connected in a loop (series):
1. A battery symbol, which shows two or more cells joined together.
2. A switch symbol, which can be drawn as open (OFF) or closed (ON).
3. A bulb symbol, representing the light.
All these are joined together with straight lines that represent the connecting wires, forming a complete path.
In simple words: Draw a loop with a bulb at the top, a switch on one side, and a battery at the bottom. Use straight lines to show the wires.

Exam Tip: Remember to use straight lines and standard symbols when drawing circuit diagrams in science exams.

Question 6. In Fig. 3.18: (i) If S₂ is in ‘ON’ position, S₁ is in ‘OFF’ position, which lamp(s) will glow? (ii) If S₂ is in ‘OFF’ position, S₁ is in ‘ON’ position, which lamp(s) will glow? (iii) If S₁ and S₂ both are in ‘ON’ position, which lamp(s) will glow? (iv) If both S₁ and S₂ are in ‘OFF’ position, which lamp(s) will glow?

Answer: If we assume that S₁ acts as the main switch for the circuit:
(i) No lamp will light up. Since S₁ is switched OFF, the entire main path is broken and no electricity can flow.
(ii) Only lamp L₁ will light up. When S₁ is turned ON, the loop for L₁ is finished, but since S₂ is OFF, the path to L₂ remains broken.
(iii) Both lamps L₁ and L₂ will light up. Since both switches S₁ and S₂ are turned ON, the entire circuit is fully complete, allowing electricity to reach both bulbs.
(iv) No lamp will light up. With both switches turned OFF, there is no complete path for electricity to travel.
In simple words: For any light to turn on, the main switch S₁ must be ON. If S₁ is ON and S₂ is ON, both bulbs glow. If S₁ is ON but S₂ is OFF, only L₁ glows.

Exam Tip: In series-parallel circuits, trace the path of electricity from the battery to each bulb to see if the switches are closed.

Question 7. Vidyut has made the circuit as shown in Fig. 3.19. 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?
Answer: Possible Reasons:
1. The thin wire (filament) inside the bulb is broken or the bulb is fused.
2. The cell is weak, dead, or not working.
3. The connections at the joints are loose or not touching properly.
4. One of the wires has a hidden break inside its cover.
5. The switch is broken and does not complete the connection inside.
6. The cell is placed backwards (wrong polarity).
7. The plastic covering at the ends of the wires was not peeled off.

Troubleshooting Steps:
To find out the problem, check each part step-by-step:
- Check if the bulb glows with a fresh cell to see if it is working.
- Try a new cell in the circuit to see if the old one was dead.
- Make sure all wire ends are tightly connected and touching metal directly.
- Look closely at the wires to check for any cuts.
- Bypass the switch with a direct wire to see if the switch is faulty.
In simple words: The bulb might not glow because of a dead cell, a fused bulb, loose wires, or a broken switch. You should check each part one by one to find the problem.

Exam Tip: When listing reasons for a faulty circuit, group them into bulb issues, cell issues, and wire issues to make your answer easy to read.

Question 8. In Fig. 3.20, in which case(s) the lamp will not glow when the switch is closed?
Answer: The bulb will not light up if the loop is broken, the battery is facing the wrong way, or there is a short circuit. Let us look at each case in Fig 3.20:
- **(a)** This is a correct series circuit, so the lamp will glow.
- **(b), (c), and (d)** These diagrams have mistakes. The lamp will not glow in these cases because the connections are wrong, the wires bypass the bulb (short circuit), or the parts are not linked properly.
In simple words: Only circuit (a) is connected correctly to make the bulb glow. In (b), (c), and (d), wrong connections or short circuits will keep the bulb off.

Exam Tip: To find out if a bulb will glow, trace a continuous line from one terminal of the cell, through the switch and bulb, and back to the other terminal.

Question 9. Suppose the ‘+’ and ‘-‘ symbols cannot be read on a battery. Suggest a method to identify the two terminals of this battery.
Answer: You can use an LED (Light Emitting Diode) to find the terminals. An LED has two wires (leads): a longer one and a shorter one. The longer wire is positive, and the shorter one is negative. Since an LED only allows current to pass in one direction, it will light up only if its longer lead is joined to the positive side of the battery, and its shorter lead is joined to the negative side. By checking which way makes the LED glow, you can easily label the battery's positive and negative terminals.
In simple words: Connect an LED to the battery. When the LED lights up, the positive side of the battery is connected to the longer wire of the LED.

Exam Tip: Always mention that an LED has polarity (a longer positive lead and a shorter negative lead) to score full marks.

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. (ii) Write the procedure that you will follow. (iii) With the items, carry out the activity to identify the cells that are working.
Answer: (i) **Materials Needed:** A bulb or LED that is in working condition, some connecting wires with their ends stripped of plastic, and a cell holder (optional).
(ii) **Steps to Follow:**
1. Create a basic testing circuit with the bulb and wires, leaving a gap where you can connect one cell at a time.
2. Put cell A into this gap.
3. Check if the bulb lights up. Write down if cell A is working or not.
4. Take out cell A, and then repeat the same steps for cells B, C, D, E, and F one by one.
(iii) **Observation:** A cell is working if the bulb lights up, and it is dead if the bulb does not glow.
In simple words: Make a simple circuit with a bulb. Test each of the six cells in it one by one. The cell is good if the bulb lights up.

Exam Tip: In design-an-activity questions, divide your answer clearly into three parts: materials needed, steps, and observation.

Question 11. An LED requires two cells in series to glow. Tanya made the circuit as shown in Fig. 3.21. Will the lamp glow? If not, draw the wires for correct connections.

Answer: No, the bulb will not glow. This is because the cells are not connected the right way. In series, you must connect the positive terminal (metal cap) of the first cell to the negative terminal (flat bottom) of the second cell.

Correct Wiring: Connect the positive terminal of one cell to the negative terminal of the next. Then, connect the remaining positive terminal to the longer wire (positive lead) of the LED, and the remaining negative terminal to the shorter wire (negative lead) of the LED.
In simple words: The bulb won't light up if you put the batteries in backwards. Connect the positive cap of one battery to the flat bottom of the other.

Exam Tip: Remember that cells in a battery must face the same direction (positive to negative) to work.

Class 7 Science Curiosity Chapter 3 Very Short Answer Type Questions

Question. What is the function of a switch in an electric circuit?
Answer: A switch is used to either complete or break a circuit. It controls whether electric current can flow or not.
In simple words: A switch turns the electricity on or off in a circuit.

Exam Tip: Use terms like "completes" or "breaks" the circuit to get full marks.

Question. What does an electric cell provide to a circuit?
Answer: An electric cell gives the electrical energy needed for the circuit to work.
In simple words: A cell is the power source that makes the electricity flow.

Exam Tip: Always describe a cell as a source of energy or power.

Question. Name the two terminals of a cell.
Answer: The two terminals are the positive terminal and the negative terminal.
In simple words: Every cell has a plus (+) side and a minus (-) side.

Exam Tip: In diagrams, remember that the longer line is positive and the shorter, thicker line is negative.

Question. Why does an LED glow only in one direction?
Answer: An LED lights up in only one direction because current can only travel through it from its positive side to its negative side.
In simple words: Electricity can only flow through an LED one way, so it must be connected correctly to glow.

Exam Tip: Remember that "LED" stands for Light Emitting Diode, and diodes only allow current to flow in one direction.

Question. What is a filament in an incandescent lamp?
Answer: A filament is the very thin wire inside a bulb. It heats up and glows brightly when electricity flows through it.
In simple words: The filament is the small wire inside a bulb that lights up when it gets hot.

Exam Tip: If the filament breaks, the bulb becomes fused and will not work.

Class 7 Science Curiosity Chapter 3 Short Answer Type Questions

Question. Why is it important to connect electric cells in a particular order in a torch?
Answer: It is necessary to connect cells in a specific way so they form a proper series. Connecting the positive end of one cell to the negative end of the next lets the current flow and lights up the torch bulb.
In simple words: Batteries must face the same direction so their power combines to turn on the torch.

Exam Tip: Use the term "series connection" to describe how cells are arranged in a torch.

Question. What happens when the filament of an incandescent lamp breaks?
Answer: When the filament breaks, the bulb is considered fused. The path for electricity is cut, so current cannot flow and the bulb will not light up.
In simple words: A broken filament breaks the circuit inside the bulb, so the bulb stays dark.

Exam Tip: A broken filament acts exactly like an open switch in a circuit.

Question. What do we mean by an electrical circuit?
Answer: An electrical circuit is a continuous, unbroken path that lets electric current flow from the positive side of a cell, through a device like a bulb, and back to the negative side.
In simple words: A circuit is the complete loop that electricity travels around.

Exam Tip: For electricity to flow, the path must be completely closed from one end of the cell to the other.

Question. Why are wires covered with plastic or rubber?
Answer: Wires are covered with plastic or rubber because these materials are insulators. They block electricity from leaving the wire, which protects us from getting shocks.
In simple words: Plastic keeps the electricity safely inside the wire so we do not get a shock.

Exam Tip: Always explain that plastic and rubber are non-conductors (insulators) of electricity.

Question. How can you identify the terminals of a battery if the symbols are not visible?
Answer: You can find the terminals by looking at the cell holder. The positive side is where the metal cap of a cell sits, while the negative side is where the flat bottom of a cell rests.
In simple words: Check how the cells fit. The side touching the cell's metal bump is positive, and the flat side is negative.

Exam Tip: Remember that the metal cap of a standard cell is always positive, and the flat disc is negative.

Class 7 Science Curiosity Chapter 3 Descriptive Answer Type Questions

Question. Why do LEDs need to be connected correctly in a circuit?
Answer: LEDs can only let electricity pass through them in one specific direction. You must connect the longer positive lead to the positive end of the battery, and the shorter negative lead to the negative end. If you connect them backwards, the current is blocked and the LED will stay off.
In simple words: LEDs only work when connected the right way around because they only let current flow in one direction.

Exam Tip: Clearly state that an LED does not glow if the connections are reversed.

Question. Explain the difference between conductors and insulators with examples.
Answer: Conductors are materials that let electricity pass through them with ease, such as copper and aluminium. Insulators are materials that do not allow electricity to flow through them, such as glass and rubber. We make wires out of conductors, but cover them with insulators to keep us safe.
In simple words: Conductors let electricity pass through, while insulators stop it. Copper is a conductor, and plastic is an insulator.

Exam Tip: Use a table format or clear headings for "Conductors" and "Insulators" with examples for each to make your answer structured.

Question. Why is copper commonly used for making wires and not gold or silver?
Answer: Even though silver and gold let electricity flow slightly better, we use copper because it is much cheaper and very easy to find. This makes copper a practical choice for making wires.
In simple words: Copper is used because it works very well, costs much less, and is easy to find compared to gold or silver.

Exam Tip: Always mention two factors: cost (cheaper) and availability (abundant).

Question. What is a circuit diagram and why is it used?
Answer: A circuit diagram is a drawing that represents an electrical setup using standard science symbols. We use it because it makes drawing and explaining circuits much simpler and clearer for everyone.
In simple words: It is a simple drawing of a circuit using symbols instead of real pictures. It helps us understand how the parts connect.

Exam Tip: Remember that circuit diagrams use straight lines to show connecting wires.

Question. How does a homemade switch work in a circuit?
Answer: In a homemade switch, a metal safety pin is connected to drawing pins on a board. If the safety pin touches both drawing pins, the path is complete and electricity flows. When you move the safety pin away, the loop breaks and the current stops.
In simple words: Touching the safety pin to both pins turns the circuit on. Pulling it away turns it off.

Exam Tip: Explain both the "ON" (closed path) and "OFF" (open path) states of the homemade switch.

Class 7 Science Curiosity Chapter 3 Exploring Questions

Question. Why is it dangerous to use damaged wires or switches?
Answer: Using broken wires or switches is dangerous because the bare metal inside can get exposed. Since the human body conducts electricity, touching these parts can cause a severe shock, painful burns, or even death. Broken electrical parts should always be changed right away.
In simple words: If wire covers are broken, you can touch the bare metal and get a dangerous electric shock.

Exam Tip: Mention that the human body is a conductor to explain why touching bare wires is risky.

Question. How would you test whether a cell is working or not using a simple circuit?
Answer: To test a cell, connect it to a simple setup with a good bulb and wires. If the bulb lights up, the cell is active and working. If it stays dark, either the cell is dead or the wire contacts are not proper.
In simple words: Connect the cell to a working bulb. If it lights up, the battery is good.

Exam Tip: Always ensure that the testing bulb is known to be in working condition before testing the cell.

Question. If electricity is unavailable in your home for two days, list five daily tasks that would be affected.
Answer: If we lose power for two days, many common chores will stop:
1. Turning on lights at night.
2. Keeping food fresh in the fridge.
3. Charging phones and laptops.
4. Watching television or using WiFi.
5. Pumping water to the overhead tanks.
In simple words: Without electricity, we cannot use lights, refrigerators, phones, televisions, or water pumps.

Exam Tip: Make sure to list simple, daily activities that directly rely on electricity.

Question. Why do LEDs last longer and are more efficient than incandescent lamps?
Answer: LEDs last much longer because they do not use thin filaments that can break or burn out. Also, they are highly efficient because they convert almost all their electrical energy into light instead of wasting it as heat.
In simple words: LEDs do not get hot and do not have a delicate wire inside to break, so they last a long time.

Exam Tip: Focus on two reasons: the absence of a filament, and less heat production.

Question. Design an activity using a conduction tester to test if a material is a conductor or insulator.
Answer: Set up a simple loop with a cell and a bulb, leaving two wire ends disconnected. Touch both open wire ends to the object you want to test. If the bulb lights up, the item is a conductor. If the bulb remains off, the item is an insulator. You can test common objects such as metal keys, plastic rulers, wooden blocks, and metal spoons.
In simple words: Touch two free wire ends to an object. If the bulb lights up, it's a conductor; if not, it's an insulator.

Exam Tip: Clearly write the conclusion: bulb glows = conductor, bulb does not glow = insulator.

Let Us Discuss about Class 7 Science Curiosity Chapter 3

Question. How does Class 7 Science Curiosity Chapter 3 explains about the glow of a torchlight only when the switch is turned ON in?
Answer: The chapter explains that a torch only lights up when the switch is turned ON because this completes the electric loop. A complete circuit allows electricity to leave the positive terminal of the battery, flow through the bulb, and return to the negative terminal. The switch works like a small gate - when it is OFF, there is a physical gap, so current cannot flow and the bulb stays dark. When the switch is flipped to ON, it bridges that gap, completing the path and turning the light on. This basic idea of open and closed paths is key to how all electrical appliances work.
In simple words: Flipping the switch to ON closes the path for electricity. Current can then flow from the battery to the bulb and back, making it light up.

Exam Tip: Be sure to use the terms "closed circuit" for ON and "open circuit" for OFF when writing your answers.

Question. Why can’t we use materials like plastic or wood instead of metal wires in circuits according to Class 7 Science Curiosity Chapter 3?
Answer: We cannot use wood or plastic instead of metal wires because they are insulators. Insulators block electricity and do not allow current to pass. For a circuit to function, all the parts must be linked by conductors, which let electricity flow smoothly. Metals like aluminium and copper are perfect conductors and are used to make wires. Meanwhile, things like wood, plastic, rubber, and glass resist electricity, so we use them to cover wires to keep us safe. If we tried to make wires out of plastic or wood, the loop would remain broken and nothing would turn on.
In simple words: Plastic and wood are insulators and block electricity. We need metal wires, which are conductors, to let the current flow.

Exam Tip: Remember that conductors allow current to flow, while insulators resist and stop the flow of electricity.

Question. What happens if an LED is connected incorrectly in a circuit, as explained in Class 7 Science Curiosity Chapter 3?
Answer: If an LED is connected backwards, it will not glow. Unlike a simple bulb, an LED only lets electricity flow through it in a single direction. It has two leads: a longer wire (positive) and a shorter wire (negative). If you connect the battery's positive terminal to the LED's shorter wire, the current is blocked. The LED only lights up when its longer leg goes to the positive side of the battery, and its shorter leg goes to the negative side. This teaches us that some circuit components have direction rules (polarity) and must be wired correctly.
In simple words: An LED only lets electricity pass one way. If you connect it backwards, it blocks the current and will not light up.

Exam Tip: Mention "polarity" and explain that the longer lead must connect to the positive terminal of the cell.

Question. What is the most important topic related to Class 7 Science Curiosity Chapter 3?
Answer: The key topic in this chapter is learning how electric circuits work and how parts like batteries, wires, bulbs, switches, and LEDs work together. It is also highly important to know how to draw standard circuit diagrams, understand closed and open circuits, and learn about the differences between conductors and insulators. These basic lessons build the foundation for more advanced science classes later on.
In simple words: The most important thing to learn is how a circuit works and how switches, batteries, bulbs, conductors, and insulators function.

Exam Tip: Make sure you practice drawing standard symbols for cells, batteries, switches, and bulbs, as they are frequently tested.