Reviewing SCERT Kerala Syllabus 7th Standard Basic Science Notes Pdf and Class 7 Basic Science Chapter 3 Question Answer Notes Solutions Pdf The World of Electricity can uncover gaps in understanding.
The World of Electricity Class 7 Questions and Answers Notes
Class 7 Basic Science Chapter 3 The World of Electricity Question Answer Pdf
Basic Science Class 7 Chapter 3 Question Answer Kerala Syllabus
Let Us Assess
Question 1.
What is the energy change in a battery when it is connected to an emergency lamp?
a) Electrical energy changes into light energy
b) Light energy changes into chemical energy
c) Chemical energy changes first into electrical energy and then into light energy
d) Chemical energy changes into electrical energy
Answer:
c) Chemical energy changes first into electrical energy and then into light energy
Question 2.
Of the following, which is in an open circuit?
a) Rotation of fan
b) A damaged bell is switched on
c) Working of a mixie
d) Glowing of a bulb
Answer:
b) A damaged bell is switched on
Question 3.
From where do the artificial satellites get electricity for its working?
a) Solar panel
b) Diesel
c) Petrol
d) Coal
Answer:
a) Solar panel
Question 4.
Sometimes there is power shortage in Kerala during summer season.Why?
Answer:
During the summer, water levels in hydroelectric dams decrease, leading to reduced electricity generation.
Question 5.
A person is standing in water. An electric line breaks and falls into the water. Is the person likely to get an electric shock? Give reason.
Answer:
Yes, the person is likely to get an electric shock because water is a good conductor of electricity.
Question 6.
Observe the diagram of an open circuit. Convert it to a closed circuit using appropriate symbols and draw it
Answer:
Class 7 Basic Science Chapter 3 Extended Activities Answers
A) Construct electric circuits using different devices and battery.
Answer:
Hint:
Simple Circuit with a Bulb
- Connect the battery to the bulb using wires.
- Connect one end of a wire to the positive terminal of the battery.
- Connect the other end of the same wire to one terminal of the bulb.
- Connect another wire to the other terminal of the bulb.
- Connect the free end of this wire to the negative terminal of the battery.
- When the circuit is complete, the bulb should light up.
Adding a Switch to the Circuit
- Construct the simple circuit with a bulb as described above.
- Insert a switch into the circuit by connecting it between one of the wires.
- Open the switch to break the circuit and turn off the bulb.
- Close the switch to complete the circuit and turn on the bulb.
Using an LED
- Connect the positive terminal of the battery to the longer leg (anode) of the LED.
- Connect the shorter leg (cathode) of the LED to a wire.
- Connect the other end of this wire to the negative terminal of the battery.
- The LED should light up. If it doesn’t, try reversing the connections.
B) Construct a model of a hydroelectric power station and explain its working. .
Answer:
Hint:
Steps to Build the Model:
- Prepare the Shoebox: Cut a rectangular hole in the lid of the shoebox, large enough to fit the plastic tub/container.
- Create the Water Reservoir: Place the plastic tub/container inside the shoebox. This will represent the reservoir where water collects.
- Build the Dam: Cut a piece of cardboard or foam board to fit across the opening of the shoebox, leaving space for the water to flow underneath. This will represent the dam. Glue the dam in place.
- Add the Water Wheel: Attach the toy water wheel to one side of the dam, inside the shoebox. Make sure it can spin freely.
- Connect the Generator: Attach the toy generator to the axle of the water wheel. This is the part that will generate electricity.
- Decorate (Optional): You can paint the shoebox to look like a mountain or a landscape with rivers and lakes using blue paper or paint.
How it works:
- Water Collection: Water is collected in a reservoir, like a lake.
- Dam: A dam holds back the water, creating pressure.
- Water Wheel: Water flows through the dam. spinning a wheel.
- Generating Electricity: The spinning wheel turns a generator, making electricity.
- Powering Things: The electricity can be used to power lights, toys, or charge batteries
Class 7 Basic Science Chapter 3 Intext Question and Answers
Question 1.
Above is a scene from home. Haven’t we experienced similar situations at our home as well?
Answer:
Yes.
Question 2.
What do we usually do to get light when there is a power failure?
Answer:
- Candles are used.
- Flashlights or torches are used.
- Oil lamps are used.
- Battery-powered lanterns are used.
Question 3.
Do you have an emergency lamp at your home? cr>l6BT3g}6)s nI)§lG6rr50?
Answer:
Yes
Question 4.
What are the things needed to make an emergency lamp? Write them in the Science Diary based on the following indicators.
a. How will we get the electricity to make the emergency lamp work?
b. Don’t we need a bulb to get light?
c. How will we connect each part?
d. How will we make a stand?
Answer:
a. We need batteries to provide electricity.
b. Yes, we need a light bulb or an LED to produce light.
c. Use wires to connect the batteries to the light bulb.
d. Use a piece of wood or cardboard to make a simple stand to hold the bulb and batteries.
Availability of Electricity:
| Electricity: It is a form of energy that can be easily converted into many other forms. |
Question 5.
Where do we get electricity from? Pictures of some devices are given below. Observe them. Where does each of these devices get its electricity from? Write it down in the Science Diary.
Answer:
- Remote: Gets electricity from batteries, e Clock: Gets electricity from batteries.
- Mobile: Gets electricity from a rechargeable battery.
- LED Lamp: Gets electricity from a power batteries.
- Iron Box: Gets electricity from AC mains (Power supply)
Electric cells are devices that can convert chemical energy into electrical energy. Electrical energy is stored as chemical energy in them. This chemical energy is converted into electrical energy when we use them.
Question 6.
Have you heard of cell and battery? What is the difference between cells and batteries? Look at the pictures below. What is the difference between them?
Answer:
Figure 1 is a cell. Figure 2 is battery. A cell is a single unit that produce electricity chemically. A battery is an arrangement made by connecting more than one cell into a single unit.
Question 7.
Observe the pictures (A, B, C) in which the cells are connected in three different ways.
a) Do all of them represent the right way for making a battery?
b) Which among them is wrong?
c) Which one will give more electricity?
Answer:
a) No
b) B is wrong
c) C will give more electricity. When you add more cells to make a battery, the electricity gets stronger.
- A cell is a small device that produces electricity from chemicals inside it.
- A battery is made up of two or more cells connected together to produce electricity.
Question 8.
Observe the pictures given below.
a) From which source do these two devices get electricity?
b) What is the difference between the sources of electricity used in these devices?
Answer:
a) Clock: Gets electricity from cell.
Mobile: Gets electricity from a rechargeable battery.
b) The clock usually uses a small battery or a cell that cannot be used again when its charge is completely used up, while a mobile phone needs a bigger battery which is rechargeable.
Cells – Rechargeable and Non-rechargeable
Question 9.
What would you do if the cell in a clock is not working? What if your mobile phone runs out of charge?
Answer:
A cell in a clock cannot be used again when its charge is completely used up. But the battery in mobile phones can be recharged and used again.
Question 10.
You may be using rechargeable and non-rechargeable cells in different devices at home. Classify them and write in your Science Diary.
Answer:
Rechargeable Cells:
- Mobile Phones
- Laptops
- Digital Cameras
- Remote Controlled Toys
Non-Rechargeable Cells:
- TV Remote
- Wall Clocks
- Flashlights
- Watch
Question 11.
Observe this picture. What kind of bulbs are used in emergency lamps?
Answer:
Light Emitting Diode bulbs or Incandescent Bulbs.
Question 12.
What are the advantages of using LED?
Answer:
- Saves Energy.
- Lasts Longer.
- Brighter Light.
- Eco-friendly.
- Safe.
Filament Bulb: A traditional bulb that glows when electricity passes through the filament due to the heating up of the filament, but it wastes a lot of energy as heat.
CFL (Compact Fluorescent Lamp): CFL requires less energy compared to filament lamps. CFL was widely used till recently. But nowadays CFL is not commonly used.
Light Emitting Diode (LED): LED bulbs require less energy than CFL. New generation LED bulbs have also been invented recently.
Question 13.
What is an LED module?
Answer:
LED module is an arrangement of more than one LED bulb in a strip.
Question 14.
Don’t you have connecting wires, LED module, 9 V battery and a connector in your Science Kit? Try to light up the LED module using them. Do this experiment in groups and present in the class. Could all the groups light up the bulb? Draw the mode of connection in your Science Diary.
Answer:
Hint:
- Gather materials: LED module, connecting wires, 9V battery, and connector.
- Connect the positive (+) terminal of the LED module to the positive terminal of the battery using a ware.
- Connect the negative (-) terminal of the LED module to the negative terminal of the battery using another wire.
- Ensure the connections are secure.
- The LED should light up if the connections are correct and the battery has power.
- Groups can try the experiment and draw the connections in their Science Diary.
- Some groups-may face challenges if connections are not properly made or if the battery is drained.
Question 15.
Haven’t you lighted the LED bulb. Write down the electric source, electric device and connecting wire used.
Answer:
Electric source – 9V battery
Conducting wire- Copper wire
Electric device – LED, Module
Question 16.
Observe the following pictures. Parts of certain circuits are represented in the pictures given below. Will the bulbs in these circuits glow? Why? Analyse the pictures and record in the Science Diary.
Answer:
The bulbs in each circuit will not glow, because wires are open. So, no current will flow through the circuit.
Closed Circuit and Open Circuit
A circuit is considered closed when it is complete. Conversely, it is termed an open circuit when incomplete. Electric devices require a closed circuit to function.
Question 17.
Are the following circuits closed or open? Why? Analyse the figures and write down in the Science Diary.
Answer:
Circuit 1 is open and circuit 2 is closed. In circuit 1 the bulb doesn’t glow. This is because the electricity cannot flow through the broken circuit to reach the bulb, so it remains off. In Circuit 2, where the circuit is closed, the bulb glows. This is because the closed circuit provides a complete path for electricity to flow from the power source to the bulb, causing it to light up.
Question 18.
We use bulbs and fans while we are in a room. Then are the circuits of the bulb and fan closed or open? Don’t you switch off the bulb and fan when you leave the room? How can we make circuits open and closed as required?
Answer:
When we’re in the room and using bulbs and fans, their circuits are closed because electricity flows through them. However, when we leave the room and switch them off, we open the circuits, stopping the flow of electricity. We can make circuits open or closed by using switches. When we turn switches ON, circuit becomes closed and current will flow through it. When the switch is turned OFF the circuit will become open and current will not flow through it.
Question 19.
Observe the picture. What arrangement do you see in the picture to turn the bulb on and off whenever required?
Answer:
A switch is there to turn the bulb ON and OFF.
Switch: Switch is a device used to make a circuit closed or open when required. A circuit becomes closed when switch is turned on. It becomes open when switch is turned off.
Different types of Switches:
Question 20.
How does electricity reach the bulb from the battery?
Answer:
The battery has stored electrical energy. Wires create a path for electricity to flow. When the switch is turned on, it closes the circuit. Electricity passes through the wires to the bulb. The electrical energy makes the bulb glow.
Question 21.
Do all substances allow electricity to pass through?
Answer:
Some materials, like metals, allow electricity to pass through easily. Other materials, like rubber, wood, and plastic, do not allow electricity to pass through.
| Substances Conduct Electricity |
Substances that do not conduct electricity |
|
|
- Plastic
- Rubber
- Wood
- Glass
|
Question 22.
You might have noticed substances which conduct electricity7 and do not conduct electricity. Design an experiment to distinguish them and present it in the class.
Answer:
Hint:
To identify and distinguish between substances that conduct electricity (conductors) and those that do not (non-conductors).
Materials Needed:
A small light bulb (LED works well), a battery (9V or similar), electrical wires , various test substances (e.g., metal spoon, plastic ruler, rubber band, piece of wood, copper wire, aluminum foil, etc.), a switch (optional)
Connect the Circuit:
- Attach the positive terminal of the battery to one end of the light bulb using an electrical wire.
- Connect the other end of the light bulb to one of the clips.
- Attach another wire to the negative terminal of the battery and connect it to the other clip.
- If using a switch, you can place it between the battery and the light bulb for easier control.
Procedure:
- Connect each test substance one by one between the clips.
- Note whether the light bulb lights up for each substance.
Observations:
- Conductors: If the light bulb lights up, the substance is a conductor of electricity. This typically happens with metals like copper wire, aluminium foil, and a metal spoon.
- Non-Conductors: If the light bulb does not light up, the substance is a non-conductor (insulator). This is typical for materials like plastic rulers, rubber bands, and wood pieces.
Activity
Take the 9 V battery, connecting wire and the LED module.from your Science Kit. Arrange them as shown in the figure. Will the LED module glow in this circuit? Why? Connect the ends marked A and B using different materials.
Materials: Safety pin, a piece of wood, paper, steel scale, charcoal, pencil graphite, plastic bangle, metal bangle, wet paper, copper wire.
Observations:
Question 23.
Which of the materials you used made the LED glow? What could be the reason?
Answer:
Safety pin, Steel scale, Pencil graphite, Metal bangle, Wet paper, and Copper wire make the LED glow. Because they are good conductors of electricity.
Question 24.
Isn’t it due to the passage of electricity through those materials?
Answer:
Yes. It is due to the passage of electricity through those materials.
Question 25.
Which materials conduct electricity?
Answer:
Safety pin, Steel scale, Pencil graphite, Metal bangle, Wet paper, Copper wire.
Question 26.
Which materials do not conduct electricity?
Answer:
Paper, Wood, Charcoal, Plastic Bangle.
Question 27.
Place your fingers over the ends of A and B in the device made for the experiment. Does the LED glow? Repeat the experiment with wet fingers. What change did you notice? Give reason. (Do not operate a switch with a wet hand. Find out the reason behind it and write it down in the Science Diary.)
Answer:
Dry Fingers: There is no glow, because dry fingers are poor conductors of electricity, so they don’t complete the circuit needed to light the LED.
Wet Fingers: LED glows because water helps conduct electricity, completing the circuit.
Question 28.
When we turn on a switch do we touch the parts through which electricity passes?
Answer:
No. The parts we touch in electrical appliances are made of insulators.
Question 29.
What about the parts that conduct electricity?
Answer:
The parts that conduct electricity, such as the wires and metal contacts inside the switch, are hidden inside the switch housing, where you can’t touch them directly.
Conductors: Conductors are the substances that allow electricity to pass through them. Examples of conductors include iron, gold, copper, steel, graphite, and water.
Insulators: Insulators are the substances that do not allow electricity to pass through. Dry wood, paper, plastic, and cloth are examples of insulators.
Question 30.
There are many situations where conductors and insulators are used. Tabulate such situations you are familiar with.
Answer:
Activity
Let’s repeat the experiment that you have done to distinguish conductors and insulators. Connect the ends A and B using each of the following substances. Materials: iron nail, copper wire, silver ornament, gold ornament, aluminium wire, a piece of zinc, lead wire, magnesium ribbon, a piece of tin sheet.
Inference: All these substances conduct electricity. They are all metals.
Different types of metallic wires:
Question 31.
Which metal do we normally use to transmit electricity though electric lines?
Answer:
Copper and Aluminium. Copper is great for electric wires because it lets electricity flow easily and is strong and flexible. Aluminium is also good, though not as good as copper, but it is lighter and cheaper, making it good for long-distance power lines.
Question 32.
What is the reason for not using copper wire in electric lines? Inquire.
Answer:
- Cost: Copper is more expensive than other materials like aluminium.
- Weight: Copper is heavier than aluminium. Heavier wires need stronger support structures, like poles and towers, to hold them up.
- Availability: Aluminium is more abundant and easier to get in large quantities.
Question 33.
Haven’t you prepared separate circuits for operating LED module and mini motor? What will happen if you include all of them in the same circuit?
Answer:
Different devices like an LED module and a mini motor have different power requirements. Combining them in the same circuit can cause problems like overloading and device damage.
Question 34.
Do all the devices in your home start function when a single switch is turned on?
Answer:
In your home, each device (like lights, fans, TV) has its own switch. This allows you to turn on only the device you need without affecting others.
Question 35.
If so, how many circuits will be needed in the house?
Answer:
Separate circuits for different areas. Different devices need different circuits to function properly and safely.
Question 36.
What tools did you use to make the circuits? Haven’t you seen electricians use different tools for different purposes such as cutting wire, stripping off insulation and testing electric current.
Observe the pictures. Find out the uses of each of the below tools from an electrician.
Answer:
Cutting Pliers: Electricians use cutting pliers to cut wires.
Wire Stripper: Wire strippers are used to remove the plastic coating from wires without cutting the wire itself.
Screwdriver: Screwdrivers are used to tighten or loosen screws.
Tester: A tester checks if a wire or device has electricity flowing through it.
Question 37.
Observe the given circuits. Identify the parts marked A, B, C and D.
Answer:
Circuit 1:
A – Unit bulb
B – Cell
C – Open switch
D – Wire
Circuit 2:
A – Glowing bulb
B – Cell
C – Closed switch
D – Wire
Question 38.
What are the differences between the two circuits?
Answer:
Circuit 1 is open circuit. So, no current flows through it. Circuit 2 is closed circuit, so current flows through it.
Question 39.
Draw the circuits you have already made using the symbols.
Answer:
Question 40.
We can use 9 V battery and LED module for making an emergency lamp. How will you connect them to make a circuit? Try to draw it.
Answer:
Question 41.
We have used a 9 V battery to make an emergency lamp. Will we get an electric shock if we touch the wire connected to the battery?
Answer:
No. The voltage (9 V) is too low to push a dangerous amount of current through your body.
Lightning and Electricity
Have you observed the lightning during the rainy season? Clouds carry a significant
electrical charge. Lightning occurs when this charge transfers between clouds or to the
ground. Lightning strikes can lead to accidents due to their potent electric current.
Question 42.
If, somehow, the electricity used at home passes through our body, it can cause electric shock. What is the reason?
Answer:
Electricity passing through our body can cause electric shock because our body conducts electricity. The electricity we used at home is of 230 V. It is not safe to use high voltage electricity while conducting experiments.
Electric shock: We get an electric shock when electric current passes through our body. Our body is an electric conductor since water is present in the living cells. Electric shock occurs when a broken power line or an external electric source, like an uninsulated circuit comes into contact with the body. Sometimes this causes severe bums. Cardiac arrest is the major reason for death due to electric shock.
Question 43.
Observe the given situations. Find out the situations in which there is a chance for electric shock and put a tick mark (✔) in the appropriate boxes.
Answer:
Question 44.
What are the precautions to be taken while handling electrical appliances?
Answer:
- Never touch electrical appliances with wet hands.
- Always unplug appliances before cleaning or repairing them.
- Keep appliances away from water.
- Never overload electrical sockets.
- Don’t use damaged cords or plugs.
Question 45.
What happens if you try to touch or move someone who is experiencing an electric shock? Won’t we also get the shock?
Answer:
Yes. Hence one should never touch a person who has an electric shock.
Question 46.
What are the things to be done immediately to save a person who has suffered an electricshock?
Answer:
- The first thing to be done is to disconnect the electric contact. You can switch off or remove the fuse for this. If it is not possible, separate the person from the electric circuit using a dry wooden stick or some other good insulator.
- In the case of heart failure, perform chest compressions. Place one hand on top of the other and apply continuous pressure on the victim’s chest. This should be done until the heart starts beating again.
- If breathing stops, give artificial respiration. Keep the body warm by massaging.
- Take the person immediately to a hospital if the shock is severe.
Question 47.
Don’t we use a generator at school when some fairs or PTA meetings are held?
Answer:
Yes. For generating electricity.
Question 48.
Which fuel is used to operate a generator?
Answer:
The generator produces electricity making use of energy from fuels like petrol, kerosene, diesel – etc.
Question 49.
Can generators be used regularly to get electricity at home and school? Discuss on the basis of cost of diesel, pollution etc. What is the solution?
Answer:
Generators can be used regularly to get electricity at home and school, but there are important factors to consider:
Cost of Diesel: Generators run on diesel, which can be expensive. Using generators regularly may increase fuel costs significantly.
Pollution: Generators produce exhaust gases that contribute to air pollution. Regular use of generators can worsen air quality and harm the environment.
Noise: Generators can be noisy, which can be bothersome in both home and school settings.
The solution is to explore alternative energy sources like solar or wind power. Solar panels can be installed on rooftops to harness sunlight, providing clean and renewable energy. Wind turbines can also generate electricity from wind power.
Question 50.
You might have seen metallic wires stretched over tall poles. From where do these lines bring electricity?
Answer:
Electricity is brought through metallic wires stretched over tall poles from power stations.
Question 51.
How this electricity is generated?
Answer:
It is generated, often through spinning turbines using the force of falling water in hydroelectric dams or burning fuels like coal or gas.
Question 52.
How do generators in a hydroelectric power station work?
Answer:
Generators in hydroelectric power stations work using the energy obtained when water stored in reservoirs of dams falls from a height. In dams, water which is stored in reservoirs is carried through pipes and made to fall forcefully on to the turbines connected to the generators. The force of falling water rotates the turbines. The generators connected to the turbines start to work and produce electricity. This electricity is transmitted to various places through electric lines.
Question 53.
A major part of electricity produced in Kerala is from the hydroelectric power station in Idukki. Discuss the merits of hydroelectric power stations as compared to diesel generators based on cost of fuel, pollution etc.
Answer:
Hydroelectric power stations, like the one in Idukki, have several advantages over diesel generators. Firstly, they use water to produce electricity, which is free, while diesel generators need costly fuel. Secondly, hydroelectric stations produce clean energy without pollution, whereas diesel generators release harmful gases that can damage the environment and our health. Overall, hydroelectric power is cheaper and much better for the environment than using diesel generators.
Other Possibilities for Electric Power Generation
We already understood that electricity is produced in our country by using fuels like coal and diesel. We also use the power of wind and tidal waves as well as nuclear energy.
Observe the pictures given below.
- Solar cell is a device that converts solar energy into electrical energy.
- Solar panel is a combination of two or more solar cells.
- Solar energy is a solution for the future energy crisis. Cost effective technologies for harnessing solar energy are to be developed.
- Researches are going on for this purpose.
Question 54.
The production of electricity has to be increased when there is higher consumption. Doesn’t the generation of more electricity require more fuels?
Answer:
Yes.
Observe this poster.
Question 55.
What message does this poster convey?
Answer:
It reminds us to turn off lights and appliances when not in use, and to conserve energy to help protect the environment and save money on electricity bills.
Question 56.
Which are the circumstances in which electricity is wasted? Discuss.
Answer:
- Leaving lights or appliances turned on when not in use.
- Using inefficient or old appliances that consume more electricity than necessary.
- Poor insulation or drafty windows that cause heating or cooling systems to work harder.
- Overcharging electronic devices.
- Running electronics in standby mode instead of fully turning them off.
Question 57.
We have to adopt certain measures to prevent wastage of electricity and to ensure its judicious use. Prepare a poster highlighting these factors and display it in the class room.
Answer:
The World of Electricity Class 7 Notes Extra Questions and Answers
Question 1.
What is the difference between a cell and a battery?
Answer:
A cell is a single unit that produces electricity, while a battery is a collection of cells combined together to produce more power.
Question 2.
Can you recharge all types of cells?
Answer:
No, only certain types of cells, like rechargeable batteries, can be recharged multiple times by passing an electric current through them in the opposite direction of discharge.
Question 3.
What are the components of a basic electric circuit?
Answer:
A basic electric circuit consists of a source of electrical energy (such as a battery), conductors (wires), and a load (such as a light bulb).
Question 4.
What happens in an open circuit?
Answer:
In an open circuit, electric current cannot flow because the path is interrupted. As a result, the electrical components do not work.
Question 5.
Give examples of conductors and insulators.
Answer:
Examples of conductors: Copper wire, aluminium foil, iron.
Examples of insulators: Rubber, plastic, glass, wood.
Question 6.
What is electric shock?
Answer:
Electric shock occurs when a person’s body becomes part of an electric circuit, causing electricity to flow through them.
Question 7.
What should you do if someone receives an electric shock?
Answer:
Turn off the power source if possible, and if the person is unconscious, call for emergency medical assistance immediately.
Question 8.
Why is it important to never touch electrical appliances with wet hands?
Answer:
Water is a good conductor of electricity, so touching electrical appliances with wet hands can increase the risk of electric shock.
Question 9.
What is electric power generation?
Answer:
Electric power generation is the process of producing electricity from various energy sources like coal, natural gas, wind, solar, and water.
Question 10.
What is a generator?
Answer:
A generator is a device that converts mechanical energy into electrical energy.
Question 11.
How does a hydroelectric power station work?
Answer:
Water flows through turbines, causing them to spin. The turbines are connected to generators that convert the mechanical energy into electrical energy.
Question 12.
Name two simple ways to save electricity at home.
Answer:
Turn off lights when not in use and unplug electronic devices when they are not being used.
Question 13.
Observe the picture.
A) Which among the following can be used to light the bulb in the above arrangement? Why? [Copper wire, Glass, Aluminium wire, Refill, Iron wire, Rolled paper, Pencil graphite] »
B) The symbols used in circuit diagrams are given below. Name them.
C) Draw the symbols of switch ‘on’ and ‘off positions.
Answer:
A) Copper wire, Aluminium wire, Iron wire, Pencil graphite. All these are good conductor 01 electricity.
B) a- Cell,
(b is already given)
c-Wire
Question 14.
This is an electric circuit prepared by a student.
A) Which materials given below can be used to light the bulb in the circuit?
i) thick copper wire
ii) empty refill
iii) dried rib of a coconut leaf
iv) a special type of wire made up of lead and tin
v) paper
B) Which object from this can be used to arrange fuse in this circuit?
Answer:
A) Thick copper wire and a special type of wire made up of lead and tin.
B) A special type of wire made up of lead and tin: This wire, often used in fuses, can melt if too much current flows through, breaking the circuit and preventing damage to the rest of the components.
Question 15.
Notice the two circuits.
3-volt LED available from fancy shops are used in these circuits. As soon as the second circuit is turned on, the LED burns out.
A) What could be the reason for this?
B) What arrangement should be made in the circuit to prevent such damages while working?
C) What safety precautions should be taken while using electric devices?
Answer:
A) The LED bums out because battery connected with the wrong polarity. LED’s one end should be connected to the negative of battery and other should be connected with positive of battery.
B) Double-check the polarity of the LED and the battery to ensure they are connected correctly.
C)
• Never touch electrical devices with wet hands.
• Turn off devices before plugging or unplugging them.
• Use devices according to their instructions.
Question 16.
Observe the picture.
A) Which of the following materials can be used to complete the circuit and light the bulb? [pencil graphite, iron nail, glass rod, steel spoon, plastic scale, golden bangle]
B) Write the names of the devices marked 1,2 and 3 in the figure and draw the symbols.
Answer:
A)
• Pencil graphite
• Iron nail
• steel spoon
• golden bangle
B) 
Question 17.
A closed loop made up of wires and components like bulbs or motors. Electricity flows through this loop, powering devices and making them work. Without a complete circuit, electricity cannot flow, and devices won’t function.
A) ‘What ¡s an electric circuit?
B) Why do we need a switch in an electric circuit?
Answer:
A) Electric circuit is an arrangement that passes electricity from an electric source to a device. A circuit requires at least an electric source, connecting wire and an electric device.
B) We need a switch in an electric circuit to control when the electricity flows. It allows us to turn devices on and off easily, saving electricity when they are not needed.
Question 18.
Observe the Circuit.
Complete the circuit replacing the buzzer with a mini motor and make it work. Illustrate how this circuit is arranged.
Answer:
Question 19.
Some electric circuits are given below. None of the bulbs in these circuits is glowing. Identify its reason and note it down.
Answer:
None of the bulbs in these circuits is glowing. Because these circuits are open.
Question 20.
A) What is meant by a conductor? Write examples.
B) What is meant by a insulator? Write examples.
Answer:
A) Conductors are those materials which allow electricity to flow through them. Examples copper, aluminium, water, alloys of metals, graphite, electrolytes.
B) Insulators are those materials which do not allow electricity to pass through them. Examples wood, glass and plastic etc.
Question 9.
We use different types of switches in different situations. Which all you know?
Answer:
Question 21.
Which of the following is an insulator?
a) Cello tape
b) Aluminium foil
c) Wet paper
d) Steel spoon
Answer:
a) Cello tape
Question 11.
Which one of the following is not a source of electricity?
a) Solar panel
b) Electric motor
c) Storage battery
d) Generator
Answer:
Electric motor
Question 22.
Which of the following statements not applicable to LED?
a) Need less energy
b) High efficiency
c) Low cost
d) Need more electric power
Answer:
Need more electric power
Question 23.
“Due to 30% shortage of rainfall, Kerala will be in darkness. If monsoon is not received in full, we will be facing severe power crisis. This can be overcome to some extent by using electricity judiciously and avoiding its wastage.” Have you noticed the news report?
A) Write down two precautions to avoid the wastage of electricity.
B) What first aid will be given to a person affected with electric shock?
Answer:
A)
- Turn off lights and appliances when not in use: Make sure to switch off lights, fans, and other electrical devices when you leave a room.
- Use energy-efficient appliances: Choose appliances that use less electricity, like LED bulbs and energy-efficient refrigerators.
B)
- The first thing to be done is to disconnect the electric contact. You can switch off or remove the fuse for this. If it is not possible, separate the person from the electric circuit using a dry wooden stick or some other good insulator.
- In the case of heart failure, perform chest compressions. Place one hand on top of the other and apply continuous pressure on the victim’s chest. This should be done until the heart starts beating again.
- If breathing stops, give artificial respiration. Keep the body warm by massaging.
- Take the person immediately to a hospital if the shock is severe.
Question 24.
A) What may be the reason for the increase in the electricity bill of Babu?
B) Write three suggestions for reducing the use of electricity.
Answer:
A) Babu may be using more electrical appliances compared to Ammu, such as multiple fans, bulbs, and a pump set, which consume more electricity.
B)
- Turn off lights and fans when not needed: Make sure to switch off lights and fans when leaving a room or not using them.
- Use energy-efficient appliances: Replace old bulbs with LED bulbs, which use less electricity. Choose energy-efficient fans and appliances.
- Limit use of high-power appliances: Use appliances like the pump set only when necessary and avoid leaving them running unnecessarily.
Question 25.
Electricity is precious and should not be wasted. When we leave lights or fans on when not
needed, we waste electricity. Using energy-efficient appliances and turning things off when we’re not using them can help save electricity.
A) Why is it important not to waste electricity?
B) How can we save electricity at home?
Answer:
A) Electricity is important, and using it wisely helps save money and protect the environment.
B) We can save electricity by turning off lights and fans when we don’t need them and using energy- efficient appliances.
Question 26.
Electricity is generated in power plants. These plants use different sources like coal, natural gas, water, wind, or sunlight to produce electricity. The electricity is then sent through power lines to homes, schools, and buildings.
A) Where is electricity generated?
B) How does electricity reach our homes from power plants?
Answer:
A) Electricity is generated in power plants.
B) Electricity is sent through power lines from power plants to homes, schools, and buildings.
Question 27.
Hydroelectric power stations use the energy of moving water to generate electricity. They are usually built on rivers where water flows downhill. The force of the moving water spins turbines connected to generators. This process produces electricity that can power homes, schools, and industries.
A) Where are hydroelectric power stations typically built?
B) What are the advantages of hydroelectric power stations?
Answer:
A) Hydroelectric power stations are typically built on rivers where water flows downhill.
B) Advantages include clean energy generation and no fuel cost.
Question 28.
A) What is a generator?
B)Why are generators important?
Answer:
A) A generator is a machine that produces electricity by converting mechanical energy into electrical energy.
B) Generators helps in producing electricity in power stations which can be transmitted to distant areas and it helps to power up various electric devices.
Question 29.
Match the following
Answer:
| A |
B |
| Electric power production |
Hydroelectric power station |
| Electric Source |
Solar Panel |
| Electric Device |
LED Module |
| Electric Conductor |
Transmission lines |
Question 30.
Prepare posters indicating the importance of saving electricity.
Answer:
The World of Electricity Class 7 Notes
• Electricity: A form of energy that can be easily converted into many other forms.
• Sources of Electricity: Devices such as electric cells, generators, and solar cells that provide electricity are known as sources of electricity.
• Cell and Battery: A cell is a single unit that produces electricity chemically, while a battery is a collection of cells connected together to provide a greater electrical output.
■ Rechargeable Cells: Cells that can be recharged and used multiple times by restoring their charge with an external electrical source.
■ Non-rechargeable Cells: Cells that are used once and then discarded because they cannot be recharged.
• Lighting a Bulb with a Battery: Connecting a battery to a bulb with wires completes a circuit, allowing electricity to flow and light the bulb.
■ Filament Bulb: A bulb with a thin wire (filament) that glows and produces light when electricity passes through it.
■ CFL (Compact Fluorescent Lamp): An energy-efficient light bulb that uses less electricity and lasts longer than traditional incandescent bulbs.
■ Incandescent Bulb: A traditional light bulb that produces light by heating a filament wire to a high temperature.
• Electric Circuit: A complete path through which electric current flows.
• Closed Circuit and Open Circuit: A closed circuit is complete and allows electricity to flow (Circuit 2), while an open circuit is incomplete and stops the flow of electricity (Circuit 1). Electric devices need a closed circuit to work.
• Switch: A device that can open or close a circuit, controlling the flow of electricity.
• Flow of Electricity: Electricity flows from a power source through conductors, such as wires, to power devices and then back to the source.
• Conductors and Insulators: Conductors, like metals, allow electricity to flow easily, while insulators, like rubber and plastic, resist the flow of electricity.
• Symbols: It used in circuit diagrams to represent various electrical components, like batteries, bulbs, and switches.
• Electric Shock: A dangerous flow of electricity through a person’s body, which can occur if safety precautions are not followed.
• Electric Power Generation: The process of producing electricity using various methods, such as burning coal, harnessing wind, or capturing solar energy.
• Generator: A device that converts mechanical energy into electrical energy.
• Hydroelectric Power Station: A place that generates electricity by using flowing water to spin a turbine connected to a generator.
• Don’t Waste Electricity: Saving electricity by turning off lights and appliances when not in use helps conserve resources and reduce costs.
