Overview
This chapter shows that an electric current does more than light a bulb: it can make a magnet and it can produce heat, and it explains where the current in a cell comes from. You begin with a simple test in which a compass placed under a wire turns whenever the current is switched on, the same observation that led Oersted in 1820 to link electricity and magnetism. Winding the wire into a coil and adding an iron core gives an electromagnet, a magnet you can switch on and off, whose poles can be found with a compass and reversed by reversing the current, and whose strength grows with more current and more turns. Lifting electromagnets on cranes, electric bells, motors, fans and loudspeakers all use this magnetic effect. Next you see that a current warms a wire because of its resistance, why nichrome is chosen for heating elements, which household appliances depend on this heating effect, and how overheating is prevented. Finally you open up the cell itself: the Voltaic cell and a home-made lemon battery, the dry cell with its zinc case and carbon rod, rechargeable lithium-ion batteries, and why used batteries must be recycled as e-waste.
हिंदी में पढ़ें
विद्युत धारा चुंबकीय सुई को घुमा सकती है, ऐसा चुंबक बना सकती है जिसे चालू-बंद किया जा सके, और तार को इतना गरम कर सकती है कि वह चमकने लगे। यह अध्याय धारा के चुंबकीय और तापीय प्रभावों तथा धारा देने वाले सेलों और बैटरियों की भीतरी बनावट को समझाता है।
Learning Objectives
- Show with a compass that a current-carrying wire produces a magnetic field
- Make an electromagnet and explain the role of the iron core
- Find the poles of an electromagnet and state how to reverse them
- List the ways to change the strength of an electromagnet
- Explain how lifting electromagnets work and name other devices that use the magnetic effect
- Explain the heating effect of current and the factors on which the heat depends
- Name appliances that use the heating effect and describe how overheating is prevented
- Describe a Voltaic cell and build a lemon cell
- Describe the structure of a dry cell, compare it with rechargeable batteries and dispose of batteries safely
Topics in this chapter
8 topics · tap a topic title to jump straight to it.
The magnetic effect of electric current
1Think first
2The idea, in plain words
Suppose you build a circuit but you have no bulb to show whether a current is flowing. Is there another way to tell? There is, and all you need is a magnetic compass.
Stretch a long connecting wire between two nails fixed on a piece of cardboard, so that the wire sits a little above the board. Join one end of the wire to a cell and the other end to a home-made switch, and complete the circuit with a second wire. Now slide a compass under the stretched wire and let the needle settle. Watch the needle while you switch the circuit on and off a few times.
- With the switch ON, current flows and the compass needle turns away from its usual direction. We say the needle is deflected.
- With the switch OFF, the current stops and the needle swings back to its original direction.
Remember that a compass needle is itself a tiny magnet. It turns only when something magnetic acts on it. So the experiment tells us that a wire carrying a current behaves, for that time, like a magnet. When the current stops, this effect disappears.
The space around a magnet, or around a current-carrying wire, in which its magnetic effect can be felt is called a magnetic field. A compass is a simple detector of a magnetic field. The result of our experiment can now be stated in one line: an electric current flowing through a conductor produces a magnetic field around it. This is called the magnetic effect of electric current.
A bit of history. In 1820, the Danish professor Hans Christian Oersted (1777–1851) noticed during a demonstration that a nearby compass needle moved whenever he closed or opened a circuit. He did not announce it at once. He tested it carefully, and only when he was sure did he publish. Other scientists then repeated his experiment, got the same result and went on to study the link further. This is how science works: an observation, careful checking, and others confirming it.
Until then, electricity and magnetism were thought to be separate. Oersted showed that they are connected. Today this link is used in electromagnets, electric bells, motors, fans and loudspeakers.
3Worked example
- A compass under a wire turns when the switch is ON and returns when it is OFF.
- Oersted (Denmark, 1820) discovered that an electric current produces a magnetic field.
- A compass can show that current is flowing even when there is no bulb in the circuit.
4Your turn
Why does a compass needle placed under a wire turn when a current flows in the wire?
5Remember this
Electromagnets: making a magnet with a current
1Think first
2The idea, in plain words
If a single straight wire can act like a weak magnet, can we make a stronger magnet by using more wire? Let us try.
Take about 50 cm of flexible insulated wire and wind it tightly around an iron nail to form a coil. Fix it with tape. Join the two ends of the wire to a cell for just a few seconds and bring the nail close to some iron paper clips. The clips cling to the nail. Disconnect the cell and the clips drop off. (Do not keep the cell connected for long, or it will weaken quickly.)
Now let us study this step by step. Roll chart paper into a thin tube about as wide as a pencil and wind about 50 turns of insulated wire on it. Place a compass near each end of this coil.
- Coil alone, current ON: both compass needles are deflected. The coil is acting like a magnet.
- Current OFF: the needles return. The coil is no longer a magnet.
- Iron nail pushed inside the tube, current ON: the needles are deflected much more, and the ends of the nail now pick up paper clips.
A coil of wire that behaves like a magnet when a current flows through it is called an electromagnet. The iron piece placed inside the coil is called its core. The iron core makes the electromagnet much stronger, which is why most electromagnets used in real life have one.
The biggest advantage of an electromagnet over an ordinary (permanent) magnet is control. It is a temporary magnet: it works only while the current flows, and we can switch it on and off whenever we like. A bar magnet cannot be switched off.
The wire must be insulated. If bare wire were wound tightly, neighbouring turns would touch, and the current would take a short cut instead of going round and round the coil.
3Worked example
- A coil of insulated wire around an iron nail, joined to a cell, picks up paper clips.
- When the cell is disconnected, the clips fall off.
- Putting an iron nail inside a coil makes the compass deflect much more.
4Your turn
What is an electromagnet?
5Remember this
Poles and strength of an electromagnet
1Think first
2The idea, in plain words
A bar magnet has a north pole and a south pole. Does an electromagnet have poles too? A compass can tell us.
Label the two ends of the coil A and B. Place a compass near end A and switch the current on. Suppose the north pole of the compass needle turns towards end A. Since unlike poles attract, end A must be a south pole. Now move the compass to end B. This time the south pole of the needle points to B, so end B is a north pole. Just like a bar magnet, an electromagnet has two poles, one at each end, and they are opposite.
Reversing the poles. Now turn the cell around so that the current flows the other way through the coil. The compass shows that end A has become north and end B has become south. The poles of an electromagnet can be reversed simply by reversing the direction of the current. This is something we cannot do with a bar magnet.
Changing the strength. Repeat the experiment in two ways and count how many paper clips the electromagnet can hold:
- Use a battery of 2 cells, then 4 cells, with the same coil. A battery of more cells drives a larger current, so the magnetic field is stronger, the needle turns more and more clips are lifted.
- Keep 2 cells but use coils with different numbers of turns. A coil with more turns makes a stronger magnet.
| Change made | Effect on the electromagnet |
| More current (more cells) | Stronger |
| More turns in the coil | Stronger |
| Iron core inserted | Much stronger |
| Current reversed | Poles swap ends |
| Current switched off | Magnetism disappears |
Our Earth is a magnet too. A freely hanging magnet settles in the north–south direction because the Earth behaves like a giant magnet. Deep inside the Earth, the movement of liquid iron in the core produces electric currents, and these currents create the Earth’s magnetic field. Many migrating birds, fish and other animals use this field to find their way, and the field also shields life from harmful particles coming from space.
3Worked example
- If the north pole of a compass is attracted to end A, end A is a south pole.
- Reversing the cell makes the poles of the electromagnet change places.
- A coil with 100 turns makes a stronger magnet than one with 25 turns, when connected to the same cell.
4Your turn
Which change will NOT make an electromagnet stronger?
5Remember this
Lifting electromagnets and other uses
1Think first
2The idea, in plain words
At a school science exhibition, a student showed a model crane. Instead of a hook, its arm held an iron nail wrapped in wire and connected to a battery. When she closed the circuit, the nail picked up iron clips. When she opened it, the clips fell. There was no magnet in the model, only a circuit. This is a model of a lifting electromagnet.
Real lifting electromagnets are very strong electromagnets hung from cranes. The crane operator controls the magnet with a switch:
- Current ON: the electromagnet picks up iron and steel objects such as scrap metal, steel sheets or girders.
- Current OFF: the magnetic field disappears and the load is released exactly where it is wanted.
They are widely used in factories and scrap yards to move, lift and sort heavy metal items quickly. They also help to separate iron and steel from other scrap, because only magnetic materials are picked up. A permanent magnet could lift the scrap, but it could never let go of it easily. The on–off control is what makes the electromagnet so useful.
Other devices that use the magnetic effect. The magnetic effect of current is at work inside many things you use every day:
- Electric bell: an electromagnet pulls a small iron strip again and again so that a hammer strikes the gong.
- Electric motors and fans: the magnetic effect of current makes a part of the motor turn.
- Loudspeakers: a changing current in a coil makes a cone move back and forth to produce sound.
Looking ahead. We have seen that electricity can produce magnetism. In higher classes you will find that the opposite is also possible: a moving magnet can produce an electric current. This two-way link is the basis of both electric motors and the generators in power stations.
A practical thought. If a lifting electromagnet is left on for a long time, two things happen. The battery is used up, so the current falls and the magnet becomes weak. The coil also becomes warm, because some electrical energy is changed into heat. You will learn about this heating effect next.
3Worked example
- A crane in a scrap yard lifts iron scrap with an electromagnet and drops it by switching off the current.
- An electric bell uses an electromagnet.
- Motors, fans and loudspeakers use the magnetic effect of electric current.
4Your turn
What is the main advantage of a lifting electromagnet over a permanent magnet in a scrap yard?
5Remember this
The heating effect of electric current
1Think first
2The idea, in plain words
While making an electromagnet, you may have noticed that the wire became warm. Why should a wire get warm just because a current flows through it?
Let us test this with a special wire called nichrome. Fix two nails about 5 cm apart on a piece of cardboard and tie a 10 cm piece of thin nichrome wire (about 0.3 mm thick) between them. Connect it to a cell and a switch, keeping the switch OFF. Touch the wire: it feels the same as the room. Now switch ON for about 30 seconds, switch OFF, and touch the wire only for a moment. It feels warm. (Do this under a teacher’s supervision, and never hold a wire that is carrying current.)
Why does this happen? A conductor does not let current pass completely freely. It offers some opposition, called resistance. Different conductors have different resistance. Nichrome has a much higher resistance than a copper wire of the same length and thickness. Because of resistance, part of the electrical energy is changed into heat energy, and the conductor warms up. The production of heat in a conductor when a current flows through it is called the heating effect of electric current.
What does the amount of heat depend on? Repeat the activity with a battery of 2 cells instead of one, for the same 30 seconds. The wire becomes hotter, because 2 cells drive a larger current. The heat produced in a wire depends on:
- the amount of current flowing through it,
- the material of the wire (nichrome heats up much more than copper),
- the thickness and the length of the wire, and
- the time for which the current flows.
This explains why nichrome is chosen for heating devices: for a given current it produces more heat than copper does. Copper, with its low resistance, is chosen for connecting wires because we want them to stay cool.
You have already seen this effect in an old-style torch bulb (an incandescent lamp). Its thin filament glows because the current heats it until it is white hot, and the bulb itself feels warm after a while.
3Worked example
- A nichrome wire connected to a cell for 30 seconds feels warm.
- With 2 cells the same wire gets hotter than with 1 cell.
- The filament of an incandescent bulb glows because the current heats it strongly.
4Your turn
Nichrome wire is used in electric heaters mainly because it:
5Remember this
Heating appliances and electrical safety
1Think first
2The idea, in plain words
Many appliances at home are made to get hot on purpose. Think of an electric room heater, an electric stove, an electric kettle, an electric iron, a water-heating immersion rod and a hair dryer. All of them work on the heating effect of electric current.
Each of these has a heating element: a rod or a coil of wire with high resistance, through which the current flows. In some appliances, such as a room heater or a stove, you can see the element glowing red hot. In others, such as a kettle or an iron, the element is hidden inside. The idea is the same: electrical energy is changed into heat energy, and the heat is then passed to the air, water or cloth.
| Appliance | What the heat is used for |
| Room heater | Warming the air of a room |
| Electric kettle, immersion rod | Heating water |
| Electric iron | Pressing clothes |
| Hair dryer | Blowing warm air |
| Electric stove | Cooking food |
When heating is a problem. The same effect can also be unwanted:
- Wires that carry electricity over long distances heat up a little, so some energy is lost on the way.
- If too much current flows through thin wires, plugs or sockets, they can overheat. Plastic parts may melt and a fire can start.
To prevent this, the wires, plugs and sockets used at home should be rated for the current they will carry; a heavy appliance needs a thicker wire and a socket made for it. Household circuits also have safety devices that cut off the supply when the current becomes too large.
In industry. The heating effect is used on a very large scale too. In steel plants, special high-temperature electric furnaces melt scrap steel so that it can be recycled into new, usable steel.
Why use electric heating at all? Compared with burning firewood or charcoal, an electric heater or stove is clean at the point of use: it gives no smoke indoors, its heat is easy to control with a switch or knob, and it is safer for people who would otherwise breathe smoke while cooking.
3Worked example
- An immersion rod heats a bucket of water using a heating element.
- The element of a room heater glows red hot.
- A loose or under-rated socket can overheat and melt.
4Your turn
Which appliance does NOT work mainly on the heating effect of electric current?
5Remember this
How a cell makes electricity: the Voltaic cell
1Think first
2The idea, in plain words
We have used cells to light a lamp, make a magnet and heat a wire. But what is inside a cell that produces electricity? Let us look at one of the earliest cells ever made.
A Voltaic cell (also called a Galvanic cell) has two rods of different metals, called electrodes, partly dipped in a liquid called an electrolyte. The electrolyte is usually a weak acid or a salt solution, kept in a glass or plastic container. A chemical reaction between the electrodes and the electrolyte produces electricity. When the electrodes are joined through a lamp, current flows from the positive terminal, through the outer circuit, to the negative terminal. Slowly the chemicals get used up. Then the cell stops working and is called dead.
The story behind the name. In the late 1700s the Italian scientist Luigi Galvani saw that a dead frog’s leg twitched when it was touched with two different metals, copper and iron. He thought the electricity came from the frog. Alessandro Volta disagreed and believed it came from the metals. To test this, he replaced the frog’s leg with paper soaked in salt water, and he still got a current. So it was the two metals together with a liquid that made the current. This idea led to the first battery.
Make your own: a lemon cell. Push a copper wire and an iron nail into a juicy lemon, a little apart from each other. Here the copper and iron are the electrodes and the lemon juice is the electrolyte. One lemon cell is weak, so make five or six and join them in a chain: the iron nail of one lemon to the copper wire of the next. Connect an LED between the copper wire of the first lemon and the iron nail of the last lemon. If the LED does not glow, reverse its legs, because an LED lets current pass only when its longer leg (positive) is joined to the positive side of the battery. A glowing LED shows your lemon battery works. Salt water can be used in place of lemon juice.
Other metal pairs also work, such as zinc–copper, aluminium–copper and magnesium–copper. In such pairs copper acts as the positive electrode.
3Worked example
- A Voltaic cell: two different metal electrodes in an electrolyte.
- A lemon cell: copper wire and iron nail in a lemon; the juice is the electrolyte.
- Volta used salt-water-soaked paper to show the current came from the metals, not the frog.
4Your turn
In a lemon cell made with a copper wire and an iron nail, what is the electrolyte?
5Remember this
Dry cells, rechargeable batteries and safe disposal
1Think first
2The idea, in plain words
A Voltaic cell with a liquid in a jar is easy to spill and hard to carry. For everyday use we need something sealed and portable. That is the dry cell, the familiar cell used in torches, clocks and remote controls.
It is called ‘dry’ because its electrolyte is not a liquid but a thick, moist paste. Inside a dry cell:
- a zinc container forms the outer case and is the negative terminal;
- a carbon rod stands at the centre, topped by a metal cap, and is the positive terminal;
- the space between the rod and the zinc is filled with the paste-like electrolyte.
A dry cell is single-use. Once its chemicals are used up it cannot be recharged and must be disposed of. A battery is made by joining two or more cells together.
Rechargeable batteries. These can be charged and used again many times, which saves money and reduces waste. They come in all sizes: tiny ones in watches and phones, larger ones in laptops, tablets and cameras, and big ones in inverters and electric vehicles. The most common type today is the lithium-ion (Li-ion) battery. Even rechargeable batteries do not last forever. After being charged and used many times they slowly wear out, which is why an old phone needs charging more often.
Li-ion batteries depend on metals such as lithium and cobalt, which are mined in only a few parts of the world. So countries are working to secure supplies, recycle old batteries and develop new designs. Scientists are working on solid-state batteries, which use a solid electrolyte and are expected to be safer, charge faster and last longer.
Disposing of batteries safely. A ‘dead’ battery is not harmless. It may still contain acids and metals such as lead, cadmium, nickel or lithium, which can cause fires or harm the environment if thrown in ordinary garbage. Many of these materials are valuable and can be recycled. Take used batteries to an e-waste collection point.
3Worked example
- A torch cell is a dry cell: zinc case (negative), carbon rod with metal cap (positive), paste electrolyte.
- A mobile phone uses a rechargeable lithium-ion battery.
- Used batteries should go to an e-waste collection point, not ordinary garbage.
4Your turn
Why is a dry cell called ‘dry’?
5Remember this
Key Concepts
- Magnetic field
- The region around a magnet or a current-carrying wire in which its magnetic effect can be felt, for example by a compass.
- Magnetic effect of electric current
- A current flowing through a conductor produces a magnetic field around it.
- Deflection
- The turning of a compass needle away from its usual direction.
- Hans Christian Oersted
- Danish scientist who discovered in 1820 that an electric current produces a magnetic field.
- Electromagnet
- A coil of wire that behaves like a magnet when a current flows through it.
- Core
- The piece of iron placed inside the coil of an electromagnet to make it stronger.
- Temporary magnet
- A magnet whose magnetism lasts only for a time; an electromagnet works only while current flows.
- Poles of an electromagnet
- Its two ends act as a north and a south pole; reversing the current swaps them.
- Lifting electromagnet
- A strong electromagnet on a crane that lifts iron and steel when switched on and releases them when switched off.
- Resistance
- The opposition that a conductor offers to the flow of electric current.
- Heating effect of electric current
- The production of heat in a conductor when an electric current flows through it.
- Nichrome
- A wire with high resistance, used in heating elements because it produces more heat for a given current.
- Heating element
- The rod or coil of high-resistance wire in an appliance that becomes hot when current flows.
- Electrode
- Each of the two metal rods of a cell that are dipped in the electrolyte.
- Electrolyte
- The liquid or paste in a cell, usually a weak acid or salt solution, that reacts with the electrodes.
- Voltaic (Galvanic) cell
- A cell with two different metal electrodes in an electrolyte, named after Volta and Galvani.
- Dry cell
- A single-use cell with a zinc case (negative), a carbon rod with metal cap (positive) and a paste electrolyte.
- Rechargeable battery
- A battery that can be charged and used again many times, such as a lithium-ion battery.
- E-waste
- Discarded electrical and electronic items, including batteries, which need special recycling.
End-of-Chapter Trial Paper & Test Questions
Topic-wise questions to test your understanding of every concept in this chapter.
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What is the magnetic effect of electric current? Describe an activity to show it. / विद्युत धारा का चुंबकीय प्रभाव क्या है? इसे दिखाने के लिए एक क्रियाकलाप का वर्णन कीजिए।
Show answer
When a current flows through a conductor, it produces a magnetic field around it. Place a compass under a wire connected to a cell and a switch. When the switch is ON the needle is deflected, and when it is OFF the needle returns to its original direction. / जब किसी चालक में धारा प्रवाहित होती है तो उसके चारों ओर चुंबकीय क्षेत्र उत्पन्न होता है। सेल और स्विच से जुड़े तार के नीचे एक चुंबकीय सुई रखिए। स्विच ON करने पर सुई विक्षेपित होती है और OFF करने पर अपनी मूल दिशा में लौट आती है।
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Who discovered that electricity and magnetism are linked, and how did he make sure of his result? / किसने खोजा कि विद्युत और चुंबकत्व आपस में जुड़े हैं, और उसने अपने परिणाम की पुष्टि कैसे की?
Show answer
Hans Christian Oersted of Denmark discovered it in 1820, when a compass needle moved each time a circuit was closed or opened. He investigated carefully before publishing, and other scientists then repeated the experiment and got the same result. / डेनमार्क के हैंस क्रिश्चियन ओर्स्टेड ने 1820 में यह खोजा, जब परिपथ को बंद या खोलने पर हर बार चुंबकीय सुई हिली। उन्होंने प्रकाशित करने से पहले सावधानी से जाँच की, और फिर अन्य वैज्ञानिकों ने प्रयोग दोहराकर वही परिणाम पाया।
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What is an electromagnet? Why do most electromagnets have an iron core? / विद्युत चुंबक क्या है? अधिकांश विद्युत चुंबकों में लोहे का क्रोड क्यों होता है?
Show answer
An electromagnet is a coil of wire that behaves like a magnet when a current flows through it. An iron core placed inside the coil makes the electromagnet much stronger. / विद्युत चुंबक तार की वह कुंडली है जो धारा प्रवाहित होने पर चुंबक की तरह व्यवहार करती है। कुंडली के अंदर रखा लोहे का क्रोड विद्युत चुंबक को कहीं अधिक प्रबल बना देता है।
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State two ways to make an electromagnet stronger and one way to reverse its poles. / विद्युत चुंबक को अधिक प्रबल बनाने के दो तरीके और उसके ध्रुव उलटने का एक तरीका बताइए।
Show answer
It can be made stronger by increasing the current, for example by using a battery of more cells, or by increasing the number of turns in the coil. Its poles are reversed by reversing the direction of the current. / धारा बढ़ाकर, जैसे अधिक सेलों की बैटरी लगाकर, या कुंडली के फेरों की संख्या बढ़ाकर इसे अधिक प्रबल बनाया जा सकता है। धारा की दिशा उलटने से इसके ध्रुव उलट जाते हैं।
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The north pole of a compass needle is attracted to end A of an electromagnet. What are the poles at ends A and B? / चुंबकीय सुई का उत्तरी ध्रुव विद्युत चुंबक के सिरे A की ओर आकर्षित होता है। सिरों A और B पर कौन-से ध्रुव हैं?
Show answer
Unlike poles attract, so end A is a south pole. The other end, B, is a north pole. / असमान ध्रुव एक-दूसरे को आकर्षित करते हैं, इसलिए सिरा A दक्षिणी ध्रुव है। दूसरा सिरा B उत्तरी ध्रुव है।
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Why are lifting electromagnets used in scrap yards instead of permanent magnets? / कबाड़खानों में स्थायी चुंबकों के स्थान पर उठाने वाले विद्युत चुंबक क्यों प्रयोग किए जाते हैं?
Show answer
A lifting electromagnet picks up iron and steel when the current is switched on and releases them when it is switched off, so the operator can drop the load exactly where it is needed. A permanent magnet cannot be switched off. / उठाने वाला विद्युत चुंबक धारा चालू करने पर लोहे और इस्पात को उठा लेता है और बंद करने पर छोड़ देता है, इसलिए चालक भार को ठीक वहीं गिरा सकता है जहाँ चाहिए। स्थायी चुंबक को बंद नहीं किया जा सकता।
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What is the heating effect of electric current? On what does the heat produced in a wire depend? / विद्युत धारा का तापीय प्रभाव क्या है? किसी तार में उत्पन्न ऊष्मा किन बातों पर निर्भर करती है?
Show answer
The production of heat in a conductor when a current flows through it is the heating effect of electric current. The heat depends on the amount of current, the material, the thickness and length of the wire, and the time for which the current flows. / किसी चालक में धारा प्रवाहित होने पर ऊष्मा का उत्पन्न होना विद्युत धारा का तापीय प्रभाव है। यह ऊष्मा धारा की मात्रा, तार के पदार्थ, उसकी मोटाई और लंबाई, तथा धारा प्रवाहित होने के समय पर निर्भर करती है।
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Why is nichrome used in heating appliances? Name four appliances that use the heating effect. / तापन उपकरणों में नाइक्रोम का उपयोग क्यों होता है? तापीय प्रभाव पर काम करने वाले चार उपकरणों के नाम लिखिए।
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Nichrome has a high resistance, so it produces more heat for a given current than copper does. Electric irons, kettles, room heaters and immersion rods all use the heating effect. / नाइक्रोम का प्रतिरोध अधिक होता है, इसलिए समान धारा के लिए यह ताँबे की तुलना में अधिक ऊष्मा उत्पन्न करता है। विद्युत इस्त्री, केतली, रूम हीटर और विसर्जन छड़ (इमर्शन रॉड) तापीय प्रभाव का उपयोग करते हैं।
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Describe a Voltaic cell. How can you make a cell using lemons? / वोल्टीय सेल का वर्णन कीजिए। नींबू से सेल कैसे बनाया जा सकता है?
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A Voltaic cell has two electrodes of different metals partly dipped in an electrolyte, usually a weak acid or salt solution; a chemical reaction between them produces electricity. For a lemon cell, push a copper wire and an iron nail into a lemon; the lemon juice is the electrolyte. Several lemon cells joined copper-to-iron can light an LED. / वोल्टीय सेल में दो भिन्न धातुओं के इलेक्ट्रोड विद्युत अपघट्य (प्रायः दुर्बल अम्ल या लवण का विलयन) में आंशिक रूप से डूबे रहते हैं; इनके बीच रासायनिक अभिक्रिया से विद्युत उत्पन्न होती है। नींबू सेल के लिए नींबू में एक ताँबे का तार और एक लोहे की कील लगाइए; नींबू का रस विद्युत अपघट्य है। ताँबे को लोहे से जोड़ते हुए कई नींबू सेल मिलकर एक LED जला सकते हैं।
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Describe the structure of a dry cell. Why should used batteries not be thrown in ordinary garbage? / शुष्क सेल की संरचना का वर्णन कीजिए। प्रयुक्त बैटरियों को साधारण कूड़े में क्यों नहीं फेंकना चाहिए?
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A dry cell has a zinc container as the negative terminal, a carbon rod with a metal cap at the centre as the positive terminal, and a moist paste electrolyte around the rod. Used batteries may still contain acids and metals like lead, cadmium, nickel or lithium that can cause fires or harm the environment, so they should be given to an e-waste recycling point. / शुष्क सेल में जस्ते का पात्र ऋण टर्मिनल होता है, बीच में धातु की टोपी वाली कार्बन छड़ धन टर्मिनल होती है, और छड़ के चारों ओर नम लेई जैसा विद्युत अपघट्य होता है। प्रयुक्त बैटरियों में अब भी अम्ल और सीसा, कैडमियम, निकेल या लिथियम जैसी धातुएँ हो सकती हैं जो आग लगा सकती हैं या पर्यावरण को हानि पहुँचा सकती हैं, इसलिए उन्हें ई-अपशिष्ट पुनर्चक्रण केंद्र पर देना चाहिए।
Related Laws & Principles
Explore allFoundational laws & principles behind this chapter. Each one opens a full page — what it says, why it matters, five practice questions and the mistakes to avoid.