đ Detailed Explanation of Permanent and Induced Magnetism
âď¸ Basics of Magnetic Materials
Magnetic materials are substances that can be attracted or repelled by magnets. There are mainly three types of magnetic materials:
- Ferromagnetic materials (like iron, cobalt, and nickel) which can become magnets.
- Paramagnetic materials which are weakly attracted to magnetic fields.
- Diamagnetic materials which are weakly repelled by magnetic fields.
In Year 10 science, we focus mostly on ferromagnetic materials because they have the strongest magnetic effects and are used in permanent and induced magnets.
𧲠How Permanent Magnets Retain Their Magnetism
Permanent magnets are materials that produce their own persistent magnetic field. This happens because of the alignment of tiny magnetic regions called domains within the material. Each domain acts like a tiny magnet.
- In an unmagnetised ferromagnetic material, these domains point in random directions, so their magnetic effects cancel out.
- When a material is magnetised, the domains align in the same direction, creating a strong magnetic field.
- The magnet keeps its magnetism because the domains stay aligned as long as the magnet isnât heated, hammered, or dropped too hard.
Examples of permanent magnets include fridge magnets and the magnets used in electric motors.
𧲠How Induced Magnets Work
Induced magnetism happens when a magnetic material is brought close to a permanent magnet or a magnetic field. The magnetic field causes the domains inside the material to align temporarily, turning it into a magnet.
- The induced magnet only behaves like a magnet while it is near the permanent magnet.
- Once removed, the domains return to their random arrangement and the magnetism disappears.
- Induced magnets are useful in many devices, such as electromagnets and magnetic cranes.
⥠Relevance in Everyday Physics
Both permanent and induced magnetism are vital in understanding how many everyday devices work. For example:
- Permanent magnets are used in electric doorbells, fridge magnets, and magnetic compasses.
- Induced magnetism allows cranes to pick up and move scrap metal by turning metal objects into temporary magnets.
In Year 10 Physics, learning about permanent and induced magnetism helps you understand the behaviour of magnetic materials and the basic principles behind many electrical devices and machines. This knowledge also builds the foundation for more advanced topics like electromagnetism.
đ 10 Examination-Style 1-Mark Questions on Permanent and Induced Magnetism
- What type of magnet retains its magnetism permanently?
Answer: Permanent - What is the term for a material that becomes magnetic only when near a magnet?
Answer: Induced - What is the effect called when a magnetic material is magnetised by a nearby magnet?
Answer: Induction - Which metal is commonly used to make permanent magnets?
Answer: Steel - What type of material typically becomes an induced magnet?
Answer: Iron - What is the name of the region around a magnet where magnetic forces can be detected?
Answer: Field - What kind of poles attract each other, north and ___?
Answer: South - What happens to an induced magnet when the external magnet is removed?
Answer: Demagnetise - What device uses permanent magnets to convert electrical energy into mechanical energy?
Answer: Motor - What term describes the alignment of magnetic domains in a magnetised material?
Answer: Domains
đ 10 Examination-Style 2-Mark Questions on Permanent and Induced Magnetism
- What is a permanent magnet?
A permanent magnet is a material that produces its own persistent magnetic field without needing an external power source. - How does an induced magnet differ from a permanent magnet?
An induced magnet only becomes magnetic when placed near a magnetic field and loses magnetism when the field is removed. - What happens to a piece of iron when it is brought close to a permanent magnet?
The iron becomes temporarily magnetised due to the magnetic field of the permanent magnet, acting as an induced magnet. - Why do induced magnets lose their magnetism once the external magnetic field is removed?
Because the magnetic domains in induced magnets only align while influenced by an external field and revert to random orientations after. - Name one common material that can become an induced magnet.
Iron is a common material that can act as an induced magnet when placed near a magnetic field. - What is meant by magnetisation in terms of magnetic domains?
Magnetisation occurs when magnetic domains in a material align in the same direction to produce a magnetic field. - State one use of permanent magnets.
Permanent magnets are used in electric motors to create constant magnetic fields needed for rotation. - Why is steel sometimes a better material than iron for making permanent magnets?
Steel retains its magnetic domains aligned for longer, so it stays magnetised better than pure iron. - Explain what causes the magnetic field around a magnet.
The magnetic field is caused by the alignment of magnetic domains inside the magnet creating invisible field lines. - What is the role of a magnetic field in the process of induction?
A magnetic field realigns the domains in a nearby material, inducing magnetism temporarily.
đ 10 Examination-Style 4-Mark Questions on Permanent and Induced Magnetism
Question 1
Explain the difference between a permanent magnet and an induced magnet.
Answer:
A permanent magnet produces its own magnetic field all the time due to the alignment of magnetic domains inside it. These domains are tiny regions where the magnetic poles of atoms line up in the same direction. An induced magnet, however, only behaves like a magnet when it is placed near a permanent magnet or within a magnetic field. This happens because the magnetic domains in the induced material temporarily align while the magnetic field is present. When the external magnetic field is removed, the induced magnet usually loses its magnetism. Therefore, permanent magnets have a persistent magnetic field, whereas induced magnets have a temporary magnetic effect.
Question 2
Describe what happens to the magnetic domains in a piece of iron when it becomes an induced magnet.
Answer:
When a piece of iron becomes an induced magnet, its magnetic domains which were originally randomly oriented start to line up in the direction of the external magnetic field. This alignment causes the iron to produce its own magnetic field, making it behave like a magnet. The more domains that align, the stronger the induced magnetism becomes. However, this alignment is not permanent because once the external magnetic field is removed, the domains typically return to their random arrangement. This is why induced magnetism in iron is usually temporary. The ability of iron to be magnetised in this way is called the process of induction.
Question 3
Why do some materials become permanent magnets while others only become induced magnets?
Answer:
Some materials become permanent magnets because their atomic structure allows the magnetic domains to stay aligned even after the external magnetic field is removed. These materials, like steel and certain alloys, have domains that “lock” into position. Other materials, such as soft iron, have domains that easily move and align with an external magnetic field but do not remain aligned when the field is taken away. This difference is due to the atomic bonding and electron arrangement inside the material. Therefore, permanent magnets keep their magnetism because of stable domain alignment, while induced magnets lose it as their domains return to random orientations.
Question 4
How does the strength of an induced magnet change when placed closer to or further from a permanent magnet?
Answer:
The strength of an induced magnet increases when it is placed closer to a permanent magnet because the magnetic field it experiences becomes stronger. This stronger external magnetic field causes more magnetic domains inside the induced magnet to align. When moved farther away, the magnetic field weakens, so fewer domains stay aligned. As a result, the induced magnetâs magnetic strength decreases. The strength of the induced magnet is directly related to the strength of the external magnetic field it is exposed to. This is why distance affects how strong the induced magnetism is.
Question 5
Explain why steel can act as a permanent magnet but soft iron is usually only induced magnetically.
Answer:
Steel can act as a permanent magnet because its structure causes the magnetic domains to remain aligned for a long time after an external magnetic field is removed. The atoms in steel âhold onâ to the alignment due to their stronger atomic bonds. In contrast, soft iron has magnetic domains that can easily move and align with an external magnetic field but do not remain aligned when the field is no longer present. This means soft iron is only magnetised temporarily through induction. The difference comes down to the materialâs ability to keep domains aligned, which is stronger in steel than soft iron.
Question 6
What is meant by the term âmagnetic domainâ, and why is it important for magnetism?
Answer:
A magnetic domain is a tiny region within a magnetic material where groups of atoms have their magnetic moments aligned in the same direction. Each domain acts like a small magnet with a north and south pole. Magnetism in materials depends on how these domains are arranged. If the domains are randomly oriented, their magnetic effects cancel out, and the material is not magnetic. When many domains align in the same direction, their magnetic fields add up to create a strong overall magnet. Understanding magnetic domains helps explain why materials become permanent or induced magnets.
Question 7
Why does an induced magnet usually lose its magnetism quickly after removing the external magnetic field?
Answer:
An induced magnet loses its magnetism quickly after the external magnet is removed because the magnetic domains inside it are only temporarily aligned. These domains are influenced by the presence of the nearby permanent magnetâs magnetic field. Once the external field is gone, the domains no longer have a force to hold them in alignment and they return to their random arrangement. This makes the induced magnetâs own magnetic field disappear quickly. Materials that show this behavior are called soft magnetic materials. This is why induced magnetism is generally short-lived.
Question 8
Describe how you could demonstrate magnetic induction using a piece of iron and a permanent magnet.
Answer:
To demonstrate magnetic induction, take a piece of iron and bring it close to a permanent magnet without touching. At first, the iron will not attract objects like paperclips. When the iron is near the permanent magnet, you can use paperclips to show that the iron has become magnetic as it will now attract them. This happens because the magnetic domains in the iron align due to the permanent magnetâs field, inducing magnetism in the iron. If you move the iron away from the permanent magnet, the paperclips will fall off as the iron loses its induced magnetism. This simple experiment shows how magnetic induction works.
Question 9
Explain why cutting a permanent magnet in half does not destroy its magnetism.
Answer:
Cutting a permanent magnet in half does not destroy its magnetism because each piece still has aligned magnetic domains forming its own north and south poles. When a magnet is cut, new poles are created at the cut ends, so each smaller piece becomes a magnet with both north and south poles. The magnetic domains inside remain aligned in both pieces. Therefore, instead of losing magnetism, both parts now behave as smaller permanent magnets. This shows that magnetism is a property of the atomic structure, not of the magnetâs size.
Question 10
What role do electrons play in creating a magnetic field in a permanent magnet?
Answer:
Electrons create a magnetic field in a permanent magnet because they have magnetic moments due to their spin and movement around the nucleus. When electrons in atoms align their magnetic moments in the same direction, they produce a combined magnetic field. In permanent magnets, many electrons in the magnetic domains are aligned so their tiny magnetic fields add up to create a strong overall magnetic field around the magnet. This alignment is stable and causes the magnet to keep its magnetic properties. Without the electronsâ aligned magnetic moments, the material would not be magnetic.
đ 10 Examination-Style 6-Mark Questions on Permanent and Induced Magnetism
Question 1:
Explain the difference between a permanent magnet and an induced magnet. Include in your answer how each magnet is created and how long the magnetism lasts.
Answer:
A permanent magnet is a material that produces its own magnetic field without needing an external magnetic source. This happens because the domains within the magnet are permanently aligned in the same direction, creating a strong and continuous magnetic field. Materials like iron, cobalt, and nickel can be permanent magnets if they are processed correctly. On the other hand, an induced magnet is a piece of magnetic material that becomes a magnet only when placed near a permanent magnet or a magnetic field. The magnetic domains in an induced magnet temporarily align while in the magnetic field, creating a magnetic effect. However, once the external magnetic field is removed, the domains lose their alignment, and the magnetism disappears. Therefore, the magnetism in induced magnets is not permanent, and it lasts only as long as the external field is present.
Question 2:
Describe how the domains inside a material behave when it becomes a permanent magnet and compare this to what happens when a material is induced magnetically.
Answer:
Inside a permanent magnet, the tiny magnetic regions called domains are aligned in the same direction. This alignment happens during magnetisation, often through manufacturing processes like heating and cooling in a magnetic field. When domains are all aligned, their small magnetic fields add up to create a strong overall magnetic field around the material, giving it permanent magnetism. For induced magnetism, the domains in a normally non-magnetic material are randomly arranged without magnetism. When placed in a magnetic field, these domains temporarily line up, causing the material to act like a magnet. Once the external magnetic field is removed, the domains return to their random arrangement, and the material loses its magnetism. This is why induced magnetism is temporary, unlike the permanent alignment in permanent magnets.
Question 3:
Explain why iron is a good material for both permanent and induced magnets, referencing its atomic structure and domain behaviour.
Answer:
Iron is a good material for both permanent and induced magnets because of its atomic structure and how its magnetic domains behave. Iron atoms have electrons with magnetic moments that can align to produce a magnetic field. In iron, these atoms are grouped into regions called domains, each acting like a tiny magnet. When iron is made into a permanent magnet, the domains are aligned permanently by processes like heating in a magnetic field and cooling. This fixed alignment makes iron strongly magnetic all the time. For induced magnetism, iron’s domains can quickly align in response to an external magnetic field, producing a temporary magnetic field. The ease with which the domains align and re-align makes iron useful for creating both permanent and temporary magnets, because it can be strongly magnetised and demagnetised.
Question 4:
Discuss how induced magnetism is useful in everyday applications, giving two specific examples.
Answer:
Induced magnetism is very useful in everyday life because it allows materials to become temporarily magnetic just when needed. One common example is an electromagnet, used in devices like electric motors and cranes. When electricity flows through a coil around an iron core, the coil creates a magnetic field, and this field induces magnetism in the iron core, turning it into a powerful magnet to lift heavy metal objects. Another example is magnetic door catches found in cupboards and fridge doors. The metal in the door catch becomes an induced magnet when it nears the permanent magnet in the doorframe, helping to keep the door closed securely. In both cases, induced magnetism enables control and convenience, activating magnetism only when necessary.
Question 5:
Explain how a permanent magnet can induce magnetism in an iron nail. Describe what happens to the magnetic domains in the nail during this process.
Answer:
When a permanent magnet is brought near an iron nail, it induces magnetism in the nail by causing the magnetic domains inside the nail to align. Initially, the domains in the iron nail are randomly oriented, so the nail has no magnetic field. However, the magnetic field of the permanent magnet influences the nail’s domains, causing many to line up in the direction of the external field. This collective alignment creates a magnetic field in the nail, turning it into a temporary magnet. The nail now has a north and south pole and can attract small magnetic objects. The magnetism in the nail lasts only as long as the permanent magnet remains close; once removed, the domains lose their alignment and the nail stops behaving like a magnet.
Question 6:
Describe the process of magnetising a steel bar to make it a permanent magnet, and explain why the magnetism remains.
Answer:
To magnetise a steel bar and create a permanent magnet, the bar is usually placed in a strong magnetic field or rubbed with a permanent magnet. This external magnetic field causes the domains inside the steel bar to start aligning in the same direction. Unlike soft iron, steel has atoms that lock these domains in place even after the external magnetic field is removed. This means the domains remain aligned, which causes the steel bar to produce a magnetic field on its own. This permanent alignment of the domains is why the magnetism stays, giving the steel bar a permanent magnetic field. The steel bar behaves as a permanent magnet because its internal atomic structure prevents the domains from easily changing direction again.
Question 7:
Explain what is meant by magnetic hysteresis and how it relates to permanent magnets.
Answer:
Magnetic hysteresis is a property of magnetic materials that shows how their magnetism depends on their magnetic history. When a material like steel is magnetised by an external magnetic field, its domains align, but if the field is reduced or reversed, some domains resist change and retain their alignment. This means the material remains partially magnetised even without an external field, which is crucial for permanent magnets. The amount of magnetism left behind after removing the magnetic field is called remanence. Magnetic hysteresis is shown in a graph called a hysteresis loop, which shows the effect of applying and removing magnetic fields. This property explains why some materials can become permanent magnets: their domains resist random rearrangement after magnetisation.
Question 8:
Compare the magnetic strength of a permanent magnet to that of an induced magnet and explain why there is a difference.
Answer:
A permanent magnet is usually stronger than an induced magnet because its magnetic domains are permanently aligned, producing a continuous and stable magnetic field. The strength of a permanent magnet depends on how fully the domains are aligned and how well the material keeps this alignment. In contrast, an induced magnet is only magnetised when placed near a magnetic field and loses its magnetism once the external field is removed. The domain alignment in induced magnets is temporary and typically weaker, so the magnetic field created is not as strong. This difference occurs because induced magnets do not have the internal atomic arrangement needed to maintain domain alignment after removing the external magnetic influence.
Question 9:
Describe the role of induced magnets in magnetic recording devices like tape recorders.
Answer:
Induced magnets play an important role in magnetic recording devices such as tape recorders. In these devices, a magnetic tape coated with tiny magnetic particles passes over a recording head that produces a magnetic field. This field induces magnetism in the particles on the tape, aligning their domains to represent sound signals. The magnetic pattern on the tape stores the information. When the tape is played back, the magnetic patterns induce a current in the playback head, which turns back into sound. Because the magnetism in the tape is induced and changes to record different sounds, the magnetism must be temporary and responsive, which is why induced magnetism is essential in these devices.
Question 10:
Explain why not all metals can become permanent magnets, even if placed in a strong magnetic field.
Answer:
Not all metals can become permanent magnets because their atomic structures and magnetic domains differ. For a metal to be a permanent magnet, it must have domains that can be aligned and then remain locked in position after the external magnetic field is removed. Metals like iron, cobalt, and nickel have this ability due to their crystal structures and electron arrangements. However, many metals, such as copper or aluminium, have atoms that do not support permanent domain alignment, so their domains remain randomly oriented and return to that state after removing the magnetic field. Without this domain locking, these metals can only be weakly magnetised temporarily, meaning they cannot be permanent magnets regardless of the strength of the external magnetic field.
