Electricity: Magnetic and Heating Effects - Class 8 Science
A coil without an iron core can still deflect a compass needle, but:
A coil without an iron core will still deflect a compass needle (as it creates a magnetic field), but the deflection will be less than with an iron core.
The solution used in a Voltaic cell is called:
The solution used in a Voltaic cell is called electrolyte. It is usually a weak acid or salt solution.
A current carrying coil behaves like a:
A current carrying coil behaves like a magnet. This is the principle behind electromagnets.
If an electromagnet keeps running for too long, the battery will:
If an electromagnet keeps running for too long, the battery will weaken (its chemicals get used up) and eventually stop working (become dead).
When current is passed through coils made of iron, copper, aluminium, and nichrome, compass needles will show deflection:
When current passes through any conducting material (iron, copper, aluminium, nichrome), it creates a magnetic field that will deflect a compass needle.
A moving magnet can also lead to an electric current.
Just as electricity can produce magnetism, a moving magnet can also lead to an electric current. This principle is used in power generators.
Electric motors and power generators are based on the connection between electricity and magnetism.
The deep connection between electricity and magnetism is vital to our daily lives, as it forms the basis of many devices, from electric motors to power generators.
Who discovered that electricity and magnetism are linked?
Hans Christian Oersted discovered in 1820 that electricity and magnetism are linked. He noticed that whenever an electrical circuit was closed or opened, the needle of a magnetic compass lying nearby deflected.
In which year was the link between electricity and magnetism discovered?
The link between electricity and magnetism was discovered by Hans Christian Oersted in 1820.
Hans Christian Oersted was a professor at a university in:
Hans Christian Oersted (1777-1851) was a professor at a university in Denmark when he made his famous discovery about the connection between electricity and magnetism.
What happens to a compass needle when current flows through a nearby wire?
When current flows through a wire, the compass needle gets deflected from its original direction. When the current stops, the needle returns to its original direction.
What happens to the compass needle when the current in a nearby wire is stopped?
When the current stops, the magnetic effect disappears and the compass needle returns to its original direction.
The deflection of a compass needle near a current-carrying wire indicates that:
The deflection indicates that the current carrying wire has a magnetic effect on the compass needle.
Electricity and magnetism are not linked to each other.
Electricity and magnetism are linked. When electric current flows through a conductor, it produces a magnetic field around it. This was discovered by Hans Christian Oersted in 1820.
What is a magnetic field?
The region around a magnet or a current carrying wire where its magnetic effect can be felt, such as by the deflection of a compass needle, is said to have a magnetic field.
When electric current flows through a conductor, it produces:
When electric current flows through a conductor (like a wire), it produces a magnetic field around it. This phenomenon is known as the magnetic effect of electric current.
The phenomenon of production of magnetic field around a current-carrying conductor is called:
When electric current flows through a conductor, it produces a magnetic field around it. This phenomenon is known as the magnetic effect of electric current.
What happens to the magnetic field when current stops flowing?
The magnetic field disappears when the current stops flowing. This is why the compass needle returns to its original position when the circuit is opened.
Which of the following is NOT an application of magnetic effect of electric current?
Electric heaters work on the heating effect of electric current, not magnetic effect. Electromagnets, electric bells, motors, fans, and loudspeakers work on the magnetic effect of electric current.
Which devices work on the magnetic effect of electric current?
The magnetic effect of electric current has many practical applications in devices like electromagnets, electric bells, motors, fans, and loudspeakers.
The magnetic field around a current-carrying wire is permanent.
The magnetic field around a current-carrying wire is not permanent. It disappears when the current stops flowing.
What is an electromagnet?
A current carrying coil that behaves as a magnet is called an electromagnet. For practical applications, most electromagnets have an iron core to make them stronger.
What is placed in the core of an electromagnet to make it stronger?
When an iron nail is inserted in the core of the coil, the coil becomes a stronger magnet. For practical applications, most electromagnets have an iron core to make them stronger.
What happens when an iron nail is inserted in the core of a current-carrying coil?
When an iron nail is inserted in the core of the coil, the coil becomes a stronger magnet and the deflection of the magnetic compass needle is much more.
How many poles does an electromagnet have?
Just like a bar magnet, an electromagnet also has two poles—North and South.
What happens to the electromagnet when the current is stopped?
When the current is stopped, the cylindrical coil loses its magnetic effect. This is a key difference between electromagnets and permanent magnets.
Which of the following can increase the strength of an electromagnet?
The strength of an electromagnet can be increased by increasing the amount of electric current flowing through the coil or the number of turns of the coil, or both.
How can the poles of an electromagnet be reversed?
The poles of an electromagnet can be reversed by changing the direction of the current flowing through the coil.
A battery with more cells creates:
A battery with more cells gives a larger current compared to a single cell. This creates a stronger magnetic field, so the deflection of compass needle is more and the coil can attract more clips.
A coil becomes an electromagnet only when electric current flows through it.
A coil becomes an electromagnet only when electric current flows through it. When the current stops, it loses its magnetic effect.
An electromagnet with a single cell attracts more clips than with a battery of 2 cells.
This is false. A battery with more cells provides larger current, creating a stronger magnetic field. So an electromagnet with 2 cells will attract more clips than with a single cell.
An electromagnet is a temporary magnet.
An electromagnet is a temporary magnet because it only behaves as a magnet when current flows through it. When the current stops, it loses its magnetic effect.
Where are lifting electromagnets commonly used?
Lifting electromagnets are widely used in factories and scrap yards to move, lift, and sort heavy metal items efficiently.
How does a crane operator control a lifting electromagnet?
The crane operator can control the magnet by switching the current ON and OFF. When ON, it lifts objects; when OFF, the magnetic field disappears and objects are released.
What happens when the current in a lifting electromagnet is switched OFF?
When the current is switched OFF, the magnetic field disappears and the objects are released. This makes lifting electromagnets very useful for moving metal objects.
Lifting electromagnets can only lift iron and steel objects.
Lifting electromagnets can only lift magnetic materials like iron and steel. They cannot lift non-magnetic materials like wood, plastic, or aluminium.
Why does Earth behave like a magnet?
Deep inside the Earth, the movement of liquid iron in the core creates electric currents, which generate a magnetic field. This is why Earth behaves like a giant magnet.
Which animals use Earth's magnetic field for navigation?
Many migratory birds, fish, and animals use Earth's magnetic field to navigate across continents and oceans.
What does Earth's magnetic field protect us from?
The Earth's magnetic field acts as a shield, blocking harmful particles from space, and helps protect life on Earth.
Earth's magnetic field is generated by the movement of liquid iron in its core.
Deep inside the Earth, the movement of liquid iron in the core creates electric currents, which generate the Earth's magnetic field.
What happens when electric current flows through a conductor?
When an electric current passes through a conductor, it gets heated. This warming is known as the heating effect of electric current.
Why does a conductor get heated when current flows through it?
When electric current flows through any conductor, it faces some opposition or resistance to its flow. This resistance causes some of the electrical energy to be converted into heat energy.
What is resistance in the context of electric current?
Resistance is the opposition or obstruction that a conductor offers to the flow of electric current. Different conductors offer different levels of resistance.
The generation of heat in conductors due to flow of electric current is called:
When an electric current passes through a conductor, it gets heated. This warming is known as the heating effect of electric current.
Resistance causes electrical energy to be converted into:
Resistance causes some of the electrical energy to be converted into heat energy. This is the basis of the heating effect of electric current.
All conductors offer the same level of resistance to electric current.
Different conductors offer different levels of resistance to the flow of current. For example, nichrome wire offers higher resistance compared to copper wire of the same size and length.
Compared to copper wire, nichrome wire offers:
A nichrome wire offers higher resistance compared to a copper wire of the same size and length. This is why nichrome is used in heating devices.
Which wire is commonly used in electrical heating devices?
Nichrome wire is commonly used in electrical heating devices because it offers high resistance and generates more heat for a given current.
Why is nichrome wire used in electrical heating devices?
Nichrome wire is used in electrical heating devices because it offers high resistance and generates more heat for a given current compared to other wires.
The heat generated in a wire depends on:
The heat generated in a wire depends on the material, thickness, and length of the wire, the magnitude of current, and the duration for which the current flows.
When the same wire is connected to 2 cells instead of 1 cell:
More heat is generated when using 2 cells because the heat generated depends on the magnitude of the electric current. More cells provide more current.
Nichrome wire offers higher resistance than copper wire of same size and length.
Nichrome wire offers higher resistance compared to a copper wire of the same size and length. This property makes it suitable for heating devices.
Which of the following works on the heating effect of electric current?
Electric iron works on the heating effect of electric current. It contains a heating element that gets hot when current passes through it.
What is the heating element in electrical appliances?
All heating devices contain a rod or a coil of wire, called a heating element. In some appliances where this element is visible, it can be seen glowing red hot.
An incandescent lamp glows because:
An incandescent lamp glows because its filament is heated by an electric current to a very high temperature.
Which of these is NOT an electrical heating appliance?
Electric fan works on the magnetic effect of electric current (electric motor), not the heating effect. It does not have a heating element.
In steel manufacturing industries, high-temperature furnaces use:
In steel manufacturing industries, specially designed high-temperature furnaces use electric current to produce heat. This is used to melt and recycle scrap steel.
Electric room heaters, stoves, irons, and kettles all work on the same principle.
All these devices work on the principle of heating effect of electric current. They all contain heating elements that convert electrical energy to heat energy.
What problem can the heating effect of electric current cause?
The heating effect can cause problems like energy loss in wires during transmission, damage to plugs and sockets (plastic parts may melt), or even lead to fires.
What can happen if plastic parts of plugs and sockets overheat?
Overheating in appliances may cause damage to plugs and sockets where plastic parts may melt, or even lead to fires.
To prevent unnecessary heating in switchboards, we should use:
To prevent unnecessary heating in household switchboards, it is important to use appropriate wires, plugs, and sockets that are rated for the specified electric current of the connections.
Overheating in electrical appliances can lead to fires.
Overheating in appliances may cause damage to plugs and sockets where plastic parts may melt, or even lead to fires. Safety devices are placed in circuits to minimize such incidents.
A Voltaic cell is also known as:
A Voltaic cell is also known as Galvanic cell, named after the two Italian scientists Alessandro Volta and Luigi Galvani.
What are the main components of a Voltaic cell?
A Voltaic cell contains two metal plates made of different materials (called electrodes) and a liquid called an electrolyte, placed in a glass or plastic container.
What is an electrolyte?
The electrolyte is a liquid, usually a weak acid or salt solution, that helps conduct electricity between the electrodes in a cell.
What are electrodes in a cell?
The plates in a cell are called electrodes. They are made of different materials and are partly dipped in the electrolyte.
How does a Voltaic cell produce electricity?
A chemical reaction between the plates (electrodes) and the electrolyte produces electricity in a Voltaic cell.
When a cell is called 'dead', it means:
Over time, the chemicals in a cell get used up, and the cell stops working. It is then called 'dead' and cannot supply any more electricity.
When the circuit is connected, electric current flows from:
When the circuit is connected, electric current flows from the positive terminal through the circuit to the negative terminal.
A cell or battery generates electric current because of chemical reactions taking place inside it.
A cell or a battery is a device that generates electric current because of chemical reactions taking place inside it between the electrodes and electrolyte.
The Voltaic cell is named after:
The Voltaic cell gets its name from the Italian scientist Alessandro Volta who developed it.
Luigi Galvani noticed that a dead frog's leg kicked when touched with:
In the late 1700s, Galvani noticed that a dead frog's leg kicked when touched with two different metals—copper and iron.
Galvani thought the electricity came from:
Galvani thought the electricity came from the frog itself. But Volta believed the electricity came from the metals, not the frog.
Volta proved that electricity came from:
Volta used saltwater-soaked paper instead of the frog's leg and still got an electric current. This showed that it was the combination of metals and liquid that generated electric current.
Alessandro Volta and Luigi Galvani were scientists from:
Both Alessandro Volta and Luigi Galvani were Italian scientists who contributed to our understanding of electricity.
In a lemon cell, what acts as the electrolyte?
In a lemon cell, the lemon juice acts as the electrolyte, which helps conduct electricity between the electrodes.
In a lemon cell, what acts as the electrodes?
In a lemon cell, the metal electrodes are the copper wires and the iron nails. They are made of different materials.
What can be used instead of lemon juice to make a simple cell?
Salt solutions can be used instead of lemon juice as the electrolyte. Any weak acid or salt solution can work as an electrolyte.
Which of these is a common metal pair for Voltaic cells?
Some common metal pairs for Voltaic cells are zinc/copper, zinc/silver, aluminium/copper, iron/copper, magnesium/copper, and lead/copper.
In a lemon cell with copper and iron electrodes, copper acts as:
Some metals—like copper—act as positive electrodes, while some other metals—like zinc and iron—act as negative electrodes. This is due to their chemical properties.
Pure water can conduct electricity as effectively as lemon juice.
Pure water is not a good conductor of electricity. An electrolyte like lemon juice or salt solution is needed to conduct electricity in a cell.
Why are dry cells called 'dry'?
Dry cells are called 'dry' because the electrolyte is not a liquid but a thick moist paste.
In a dry cell, what acts as the negative terminal?
A dry cell consists of a zinc container which acts as a negative terminal.
In a dry cell, what acts as the positive terminal?
A carbon rod at the centre covered with metal cap acts as the positive terminal in a dry cell.
The dry cell is a:
The dry cell is a single use cell, meaning once it is used up, it has to be disposed of.
Dry cells are more portable than Voltaic cells with liquid electrolyte.
Dry cells are more portable because their electrolyte is a thick moist paste, not a liquid. This makes them convenient for everyday use.
Dry cells are less portable compared to Voltaic cells.
This is false. Dry cells are MORE portable than Voltaic cells because their electrolyte is a paste, not a liquid, making them convenient for everyday use.
What is the main advantage of rechargeable batteries?
Rechargeable batteries can be recharged and reused multiple times. This prevents wastage and saves money over time.
Which devices use rechargeable batteries?
Rechargeable batteries are used in many devices—from small batteries in watches and phones to batteries in laptops and tablets to bigger batteries that run inverters or drive electric vehicles.
What happens to rechargeable batteries after being charged and used many times?
Rechargeable batteries do not last forever. After being charged and used many times, they slowly wear out.
Why does a phone battery require charging more often after a year or two?
After being charged and used many times, rechargeable batteries slowly wear out. This is why phone batteries require charging more often after some time.
The most common type of rechargeable battery today is:
Today, the lithium-ion (Li-ion) battery is the most common type of rechargeable battery, found in almost all devices that use batteries.
Rechargeable batteries can be recharged and reused multiple times.
Rechargeable batteries can be recharged and reused multiple times. This prevents wastage and saves money over time.
Rechargeable batteries last forever and never wear out.
Rechargeable batteries do not last forever. After being charged and used many times, they slowly wear out.
Lithium-ion batteries use special metals like:
Lithium-ion batteries rely on special metals like lithium and cobalt, which are mined and processed in limited parts of the world.
What are solid-state batteries?
Solid-state batteries replace the liquid or paste-like electrolytes with solid materials. These future batteries would be safer, charge faster and last longer.
What are the expected advantages of solid-state batteries?
Solid-state batteries would be much safer, charge faster and last longer compared to current batteries.
Improved rechargeable batteries are important for developing environmentally friendly sources of electrical power.
Improved rechargeable batteries are very important as the world moves to developing environmentally friendly sources of electrical power.
Why should used batteries not be thrown in regular garbage?
Used batteries contain materials like acids and metals like lead, cadmium, nickel, or lithium, which may cause fires or be harmful for the environment.
Where should used batteries be disposed of?
Used batteries should be disposed of at special 'e-waste' recycling facilities where they can be safely processed and recycled.
Why is recycling batteries important?
Many materials used in batteries are valuable and could be recycled and reused. Recycling batteries is good for the planet and the people.
Which harmful materials might be present in used batteries?
Used batteries could contain materials like acids and metals like lead, cadmium, nickel, or lithium, which may cause fires or be harmful for the environment.
A dead battery is completely safe and can be thrown anywhere.
Even when a battery stops working, it is not completely 'dead'. It could still contain harmful materials like acids and metals which may cause fires or harm the environment.
When current flows through a nichrome wire, which effects can be observed?
When current flows through any wire including nichrome, both heating effect (wire becomes warm) and magnetic effect (compass needle deflects) can be observed.
Your Score
Tap outside or press ESC to close
NCERT Guruji