What is Magnetism?
Magnetism is a force that certain materials have to attract or repel each other. These materials are called magnets.
Types of Magnets:
- Natural Magnets: Found in nature (like lodestone).
- Artificial Magnets: Made by humans (bar magnets, horseshoe magnets, etc.).
Properties of Magnets:
- Attraction: Magnets attract magnetic materials like iron, nickel, and cobalt.
- Repulsion: Like poles of two magnets repel each other (North-North or South-South). Unlike poles attract (North-South).
- Poles: Every magnet has two poles: a North pole and a South pole.
- Directional Property: A freely suspended magnet always points in the North-South direction. This is the basis of a magnetic compass.
Magnetic Field:
The area around a magnet where its magnetic force can be felt is called its magnetic field.
Making Magnets:
- Single Touch Method: Rubbing a magnetic material with one pole of a magnet in the same direction repeatedly.
- Double Touch Method: Using two magnets to rub the magnetic material from the center outwards in opposite directions.
- Electrical Method: Passing an electric current through a coil wrapped around a magnetic material (electromagnetism).
Demagnetization:
Magnets can lose their magnetism by:
- Heating: Heating a magnet strongly.
- Hammering: Dropping or hammering a magnet repeatedly.
- Improper Storage: Not storing magnets with keepers (pieces of soft iron across the poles).
Uses of Magnets:
Magnets have many uses, including:
- Compasses for navigation.
- Holding things in refrigerators.
- Electric bells and loudspeakers.
- Separating magnetic materials from non-magnetic ones.
- In magnetic tapes and hard disks for storing information.
Test yourself
A. Objective Questions
1. Write true or false for each statement.
(a) Artificial magnets are weaker than natural magnets.
Answer : False
Artificial magnets are stronger than natural magnets.
(b) Poles of a magnet cannot be separated.
Answer : True
(c) A magnet can attract only a magnetic substance.
Answer : True
(d) A magnet has no effect when it is heated to a high temperature.
Answer : False.
A magnet gets demagnetised when it is heated to a very high temperature.
(e) Permanent magnets get easily demagnetised.
Answer : False.
Permanent magnets cannot be demagnetised.
(f) Magnetic poles occur in pairs.
Answer : True
(g) Single touch method is better than the electrical method for making a magnet.
Answer : False.
The Electric method is better than the single touch method.
(h) Magnetic keeper is a wooden piece.
Answer : False.
Magnetic keepers are the pieces of soft iron.
(i) Copper cannot be magnetised.
Answer : True
2. Fill in the blanks
(a) Temporary magnets are usually made up of———.
Ans : Soft iron
(b) Rough handling destroys the ——— properties of a magnet.
Ans : Magnetic
(c) Like poles ——– each other.
Ans : Repel
(d) A freely suspended magnet points in the ——- direction.
Ans : North-south
(e) In a magnet, ——— have the maximum attractive property.
Ans : Ends
(f) A magnet has ——– poles.
Ans : Two
3. Match the following
4. Select the correct answer
(a) If we suspend a magnet freely, it will settle in .
- east-west direction
- north-south direction
- north-east direction
- east-south direction
Answer : North-south direction
(b) Making a magnetic substance a magnet by bringing it closer to another magnet without touching it, is
- magnetic induction method
- single touch method
- double touch method
- electrical method
Answer : Magnetic induction method
(c) An example of natural magnet is
- iron
- steel
- lodestone
- none of above
Answer : Lodestone
(d) The artificial magnet used to detect direction in the laboratory is
- U-shaped magnet
- horse shoe magnet
- electromagnet
- magnetic compass
Answer : Magnetic compass
B. Short/Long Answer Questions
1) What is a magnet ?
Answer : A magnet is a material that can attract certain metals like iron and has a north and south pole
2) What are magnetic and non-magnetic substances ? Give two examples of each.
Answer : Magnetic substances are materials attracted by magnets. Examples: iron, nickel.
Non-magnetic substances are not attracted by magnets. Examples: wood, plastic
3) What are natural and artificial -magnets ?
Answer : Natural magnets are found in nature, like lodestone. 1 Artificial magnets are made by humans, such as bar magnets
4) How is an artificial magnet prepared from a natural magnet ?
Answer : Stroke it repeatedly in the same direction with one pole of an existing magnet.
- Pass electric current through a coil of wire wrapped around the iron piece.
5) State two ways of magnetising an iron piece.
Answer : To magnetize iron:
- Rub it with another magnet.
- Use electricity in a coil around it.
6) How can magnetic properties of a magnet be destroyed ?
Answer : A magnet can lose its magnetism by:
- Heat it strongly.
- Hitting it repeatedly.
7) Why does a freely suspended magnet always rest in a north- south direction ?
Answer :
A freely suspended magnet always rests in a north-south direction due to the Earth’s magnetic field.
- Earth as a Giant Magnet: The Earth itself behaves like a giant magnet.
- Magnetic Poles and Attraction: Like poles of magnets repel each other, and unlike poles attract each other.
- Alignment with Earth’s Field: When a magnet is freely suspended, it can rotate horizontally. The north pole of the suspended magnet is attracted to the Earth’s south magnetic pole (which is located near the geographic North Pole). Similarly, the south pole of the suspended magnet is attracted to the Earth’s north magnetic pole (located near the geographic South Pole).
- Coming to Rest: Due to this attractive force between the poles of the suspended magnet and the Earth’s magnetic poles, the magnet will rotate until it aligns itself with the Earth’s magnetic field lines.
8)Draw diagrams of the artificial magnets of four different shapes.
Answer:Here are four common shapes for artificial magnets:
- Bar Magnet: A simple rectangle.
- Horseshoe Magnet: Shaped like a “U”.
- Cylindrical Magnet: Like a rod or cylinder.
- Ring Magnet: Shaped like a donut.
9)Why are artificial magnets preferred over natural magnets ?
Answer:Artificial magnets are better because they can be made stronger and in various shapes to fit different needs
10)Describe an experiment to show that the maximum attractive property is at the poles of a magnet.
Answer:To show that a magnet’s pull is strongest at its ends (poles):
- Spread some iron filings evenly on a flat surface.
- Bring a bar magnet over the filings.
- Lift the magnet.
11)State four important properties of a bar magnet.
Answer:Here are four key properties of a bar magnet:
- It attracts magnetic materials like iron.
- It has two poles, North and South.
- Like poles repel, and unlike poles attract.
- A freely suspended one points North-South.
12)Explain the attractive property of a magnet with the help of an experiment.
Answer:To show a magnet attracts, place a magnet near small iron objects like pins or paperclips. You’ll observe the magnet pulling these iron items towards it, demonstrating its attractive property.
13)Describe the method by which an iron bar can be made a magnet.
Answer:You can turn an iron bar into a magnet by repeatedly stroking it in one direction with one pole of an existing strong magnet. 1 This aligns the tiny magnetic domains inside the iron, causing it to become magnetized. The more you stroke it, the stronger the resulting magnet will be.
14)How are the magnets kept safely ? What is the role of keepers in storing the magnets ?
Answer:To keep magnets safe, they should be stored in pairs with opposite poles facing each other. Often, pieces of soft iron called keepers are placed across the poles.
Keepers help by providing an easy path for the magnetic field lines to travel. This prevents the magnetic field from weakening over time by “leaking out” into the surrounding air.
15)Define the term magnetic field of a magnet. How will you recognise it experimentally ?
Answer:The magnetic field is the area surrounding a magnet where its magnetic force has an effect.
Experimentally, you can spot it by:
- Observing how iron dust lines up when scattered near the magnet.
- Noticing how the needle of a compass changes direction as you move it around the magnet.
16)How will you make an iron bar electromagnet ? Draw a diagram showing the polarities of the electromagnet.
Answer:To create an electromagnet from an iron bar, simply wind insulated wire around the bar and then connect the wire ends to a power source like a battery. Here’s a quick sketch of how it looks and which ends become the poles:
[ Battery ]
+ –
| |
\ /
‘
\
+——- Wire Coil ——-+
| |
(S) | Iron Bar | (N)
| |
+———————–+
The North (N) and South (S) poles appear at the ends of the iron bar. The direction of the current in the wire determines which end is North and which is South (use your right hand rule to figure this out!).
17)State two ways of increasing the strength of an electro Magnet
Answer:To make an electromagnet stronger, you can either pump more electricity through its wire or wrap more loops of wire around its central core.
18)Suppose you are given a long bar magnet and you are asked to break it into four small magnets. Draw diagrams showing the polarities of each broken part.
Answer:
19)State three important uses of a magnet.
Answer:Magnets are super handy in lots of ways! Here are three important uses:
- Holding things together: Think about the magnets on your fridge holding up notes or photos. They’re used in clasps for bags and jewelry too!
- Generating electricity: Big magnets are essential in power generators. When they spin near wires, they help create the electricity that powers our homes and gadgets.
- Navigation: Compasses use a magnetic needle that always points north, helping people find their way.
20) What is magnetic induction ? Explain with the help of a diagram.
Answer:Magnetic induction, also known as electromagnetic induction, is the phenomenon where a changing magnetic field in a region of space creates an electric field in any conductor within that region. This electric field can then cause electrons in the conductor to move, resulting in an induced electromotive force (EMF) or voltage, and if the circuit is closed, an induced current.
In simpler terms, if you have a magnet moving near a wire, or a changing electric current creating a changing magnetic field near a wire, you can generate electricity in that second wire without any direct contact.
Here’s a simple diagram to illustrate this:
N (Magnet)
|
v (Motion)
+——-+
| Coil |—– (Galvanometer – detects current)
+——-+
In this setup, when the North (N) pole of a magnet is moved towards the coil of wire, the magnetic field lines passing through the coil change.. If the magnet is moved away or held stationary, the magnetic field doesn’t change, and no current is induced.
21)In which direction does a suspended bar magnet come to rest? Give reason.
Answer:A suspended bar magnet comes to rest pointing in the north-south direction Reason: This happens because the Earth itself behaves like a giant magnet, having its own magnetic north and south poles. The north pole of the suspended bar magnet is attracted to the Earth’s magnetic south pole, and its south pole is attracted to the Earth’s magnetic north pole. This alignment causes the magnet to settle along the Earth’s magnetic field lines, which run approximately along the geographical north-south axis.
22)State three differences between the temporary and permanent magnets.
Answer:
| Feature | Temporary Magnets | Permanent Magnets |
| Magnetism Duration | Exhibit magnetic properties only when in the presence of an external magnetic field or electric current. They lose most of their magnetism quickly once the external influence is removed. | Retain their magnetic properties for a long time, even in the absence of an external magnetic field or electric current. |
| Materials Used | Typically made from soft magnetic materials like soft iron, which are easy to magnetize and demagnetize. | Usually made from hard ferromagnetic materials such as steel, alnico (aluminum, nickel, cobalt alloy), or neodymium alloys, which are difficult to magnetize but retain magnetism well. |
| Strength Control | The strength of a temporary magnet (like an electromagnet) can be easily controlled by varying the current or the strength of the external magnetic field. | The strength of a permanent magnet is largely fixed and cannot be easily changed after it is magnetized. While it can be weakened or demagnetized under certain conditions (e.g., heating, hammering), its strength isn’t readily adjustable. |
23) State three ways of demagnetising a magnet.
Answer :
Here are three common ways to demagnetize a magnet:
- Heating the Magnet: Heating a magnet to a high temperature (above its Curie temperature, which varies depending on the material) disrupts the alignment of the magnetic domains within the material. The increased thermal energy causes the atoms and their magnetic moments to become randomly oriented, thus significantly reducing or completely eliminating the magnet’s overall magnetic strength.
- Hammering or Subjecting to Mechanical Shock: Repeatedly striking or hammering a magnet, especially while it is oriented in an east-west direction (away from the influence of the Earth’s magnetic field), can disorganize the alignment of its magnetic domains. The mechanical vibrations provide energy that allows the domains to shift from their ordered state to a more random orientation, leading to demagnetization.
- Using an Alternating Current (AC) Magnetic Field: Placing a magnet within a strong alternating current magnetic field and then slowly withdrawing it as the strength of the AC field is gradually reduced to zero can effectively demagnetize it. The alternating field repeatedly reorients the magnetic domains in opposite directions. As the field weakens and the magnet is removed, the domains are left in a more random and less aligned state, resulting in a weaker or non-existent overall magnetic field. This method is commonly used in devices specifically designed for demagnetizing objects.
24)Suggest one way to recognise the magnetic field of the earth.
Answer:
One way to recognize the magnetic field of the Earth is by using a freely suspended magnet (like a compass needle).
Explanation:
As discussed earlier, the Earth acts like a giant magnet with its own magnetic field. When a magnet is suspended freely (allowing it to rotate horizontally), it will align itself with the Earth’s magnetic field lines.
25) Name the material of core of an electromagnet for
- temporary magnet
- permanent magnet.
Answer :
For the core of an electromagnet:
- Temporary Magnet: The core is typically made of a soft ferromagnetic material like soft iron. Soft iron is easily magnetized when current flows through the coil wrapped around it, and it loses most of its magnetism quickly when the current is switched off.
- Permanent Magnet: An electromagnet is, by its very nature, a temporary magnet. Its magnetism exists only while an electric current is flowing. Therefore, an electromagnet does not have a core made of a material intended to be a permanent magnet.
26)You are given an iron nail, a torch cell and a long piece of insulated copper wire. With the help of a labelled neat diagram, describe in steps how you will make the nail, an electromagnet.
Answer:To make the nail into a temporary magnet, just wind the copper wire tightly all around it. As long as the battery is connected, the nail will act like a magnet!
Think of it like this (no actual drawing possible here): Imagine the nail covered in loops of wire, and those wire ends are touching the ends of the battery.
27)Describe an experiment to illustrate that like poles repel while the unlike poles attract.
Answer : So, you’ve taken two simple bar magnets and a bit of string to unravel one of nature’s elegant rules. By carefully suspending one magnet and then introducing another, you’ve directly observed a key principle of magnetism: like poles repel, and unlike poles attract.
When you brought the north pole of one magnet near the north pole of the freely hanging one, you saw it swing away, almost as if an invisible cushion pushed them apart. The same thing happened when you brought the two south poles together – a definite push, a clear sign of their mutual aversion.
Then came the intriguing part where opposites met. The north pole of one magnet, when brought close to the south pole of the other, created a pull, a gentle dance where the suspended magnet willingly moved closer to its counterpart. This attraction was mirrored when you reversed the poles, south meeting north with the same eager connection.
Your experiment beautifully illustrates this fundamental law of magnetic interaction. It’s a tangible way to understand that magnets aren’t just simple pieces of metal; they possess these invisible fields that exert forces, either pushing away or pulling together, depending on the orientation of their poles. This very principle is what underlies countless technologies we use every day, from the simple compass guiding travelers to the complex workings of electric motors and generators. A truly elegant demonstration with such simple materials!
28) What are magnetic keepers ? Name its material.
Answer : As for the material, they are typically made of soft iron. This material is easily magnetized and demagnetized, which is key to their function. By providing a closed loop for the magnetic field lines, the keepers help to maintain the magnet’s internal magnetic order and prevent it from weakening
Magnetic keepers are bars made of soft ferromagnetic material that are placed across the poles of a permanent magnet when it is not in use.
Material of Magnetic Keepers:
Magnetic keepers are typically made of soft ferromagnetic materials, primarily soft iron or sometimes low-carbon steel.
29) How are the north and south poles of a magnet located ? Explain.
Answer: The poles of a magnet are the regions where its magnetic force is most concentrated, located at its ends. We can locate them by observing how the magnet aligns itself with the Earth’s magnetic field or by its interaction with the known poles of another magnet.
