Do you know that the earth’s magnetic field varies from point to point in space? Do you know what is the reason behind this? Many folks also want to understand about the region and its weak magnetic flux .
We will determine the magnitude of the moment of a magnet of a magnet with a particular degree of the uniform magnetic flux and what is going to happen if the magnet is rotated freely during a plane and what is going to be the P.E. of the magnet. Do you know once we pass through the solenoid, it acts sort of like a magnet, finding out what's the moment of a magnet of this solenoid?
We will be seeing here, what proportion torque is required for turning a magnet in order that its moment of a magnet is at a particular alignment with the sector . We will be seeing an example of a magnet wont to determine meridian points and computing the direction and magnitude of the earth’s magnetic flux . There are various examples, exemplary questions, MCQ’S and worksheets mentioned below which can assist you understand magnetism and therefore the magnetic flux with its uses and application. Practising the problems on magnetism will definitely help you in the retention of these concepts as the topics are frequently asked in examinations.
Distant galaxies, humans and beasts, tiny invisible atoms are all penetrated by magnetic fields from a spread of sources over and once again . Hence, we will say that magnetic phenomena are universal in nature. In the previous chapter, we studied the connection between electricity and magnetism. In this chapter, we take a look at magnetism in its own right. One learns the following topics in this chapter:
Description of a magnet and its behaviour in an external magnetic flux
Gauss’s law of magnetism followed up with an account of the earth’s magnetic flux
Classification of materials based on their magnetic properties
Electromagnets and permanent magnets
Important Question Related to Magnetism and Matter
Q1. Answer the following:
(a) The earth’s magnetic flux varies from point to point in space. Does it also change with time? If so, on what duration does it change appreciably?
(b) The earth’s core is understood to contain iron. Yet geologists don't regard this as a source of the earth’s magnetism. Why?
(c) The charged currents within the outer conducting regions of the earth’s core are thought to be liable for earth’s magnetism. What could be the ‘battery’ (i.e., the source of energy) to sustain these currents?
(d) the world may have even reversed the direction of its field several times during its history of 4 to five billion years. How can geologists realize the earth’s field in such a distant past?
(e ) region has a particularly weak magnetic flux of the order of 10–12 T.Answer 5.2:
(a) Earth’s magnetic field varies with time and it takes a couple of hundred years to change by an obvious sum. The variation in the Earth’s magnetic field with respect to time can’t be ignored.
(b) The Iron core at the Earth’s centre can't be considered as a source of Earth’s magnetism because it's in its molten form and is non-ferromagnetic.
(c) The radioactivity in earth’s interior is the source of energy that sustains the currents within the outer conducting regions of earth’s core.
(d) The Earth’s magnetic field reversal has been recorded several times in the past about 4 to 5 billion years ago.
(e) Due to the presence of ionosphere, the Earth’s field deviates from its dipole shape substantially at large distances. The Earth's field is slightly modified in this region because of the field of single ions. The magnetic flux related to them is produced while in motion.
(f) A remarkably weak magnetic field can deflect charged particles moving in a circle. This may not be detectable for an outsized radius path. With regard to the large region , the deflection can alter the passage of charged particles.
Answer 1:
(a) The three independent conventional quantities used for determining the earth’s magnetic flux are:
(i) Magnetic declination,
(ii) Angle of dip
(iii) Horizontal component of earth’s magnetic field
(b) The angle of dip at some extent depends on how far the purpose is found with reference to the North Pole or the South Pole . Hence, as the location of Britain on the globe is closer to the magnetic North pole, the angle of dip would be greater in Britain (About 70°) than in southern India.
(c) it's assumed that an enormous magnet is submerged inside the world with its North Pole near the geographic South Pole and its South Pole near the geographic North Pole.
Magnetic field lines originate from the north pole and terminate at the magnetic South Pole . Hence, during a map depicting earth’s magnetic flux lines, the sector lines at Melbourne, Australia would appear to maneuver faraway from the bottom.
(d) If a compass is placed in the geomagnetic North Pole or the South Pole, then the compass will be free to move in the horizontal plane while the earth’s field is exactly vertical to the magnetic poles.
FAQs on Magnetism and Matter
1. What are the key properties of magnetic field lines, and why is it frequently asked in CBSE exams why two field lines never intersect?
Magnetic field lines have several important properties that are crucial for exams. They form continuous closed loops, travel from the North pole to the South pole outside the magnet, and from South to North inside it. The density of lines indicates the strength of the field. A very important conceptual question for 2 marks is why they never intersect. If they were to intersect at a point, it would imply two different directions for the magnetic field at that single point, which is physically impossible. A compass needle placed at such a point could not point in two directions simultaneously.
2. Differentiate between paramagnetic, diamagnetic, and ferromagnetic substances. How can one expect a 3-mark question on this topic?
For a 3-mark question, you should compare these substances based on at least three distinct properties. Here’s how to structure your answer for the CBSE Board Exam 2025-26:
- Behaviour in Magnetic Field: Diamagnetic substances are feebly repelled, paramagnetic are feebly attracted, and ferromagnetic are strongly attracted.
- Magnetic Susceptibility (χ): For diamagnetic, χ is small and negative. For paramagnetic, χ is small and positive. For ferromagnetic, χ is large and positive.
- Examples: Diamagnetic (Bismuth, Copper), Paramagnetic (Aluminium, Oxygen), Ferromagnetic (Iron, Cobalt, Nickel).
3. How can a bar magnet be considered an equivalent solenoid? Which derivation from this concept is important?
A bar magnet is equivalent to a solenoid because both produce similar magnetic field patterns. A finite solenoid carrying current behaves like a bar magnet with a North and South pole. The derivation for the magnetic field at an axial point of a solenoid is an important expected question. The final expression, B = (μ₀/4π) * (2M/r³), where M is the magnetic dipole moment, is identical to that of a bar magnet at a far-axial point, proving their equivalence.
4. What are the essential magnetic elements of the Earth, and what is their practical significance?
The three magnetic elements required to specify Earth's magnetic field at any location are:
- Magnetic Declination (θ): The angle between the geographic meridian and the magnetic meridian. It's crucial for accurate navigation using a compass.
- Angle of Dip (δ): The angle between the Earth's total magnetic field and the horizontal direction. It is 90° at the poles and 0° at the magnetic equator.
- Horizontal Component (BH): The component of the Earth's total magnetic field in the horizontal plane. It is used to determine the direction in a compass.
5. Why is soft iron used for the core of electromagnets while steel is used for making permanent magnets? This is a high-order thinking question.
This is a classic HOTS question based on material properties. The choice depends on retentivity and coercivity.
- Electromagnets: They need to be strong when the current is on and lose magnetism when the current is off. Soft iron has high permeability (gets strongly magnetised) and low retentivity (loses magnetism easily), making it the ideal choice.
- Permanent Magnets: They need to retain their magnetic properties once magnetised. Steel has high retentivity and high coercivity, meaning it stays magnetised and is difficult to demagnetise, making it suitable for permanent applications.
6. From an exam perspective, is 'Magnetism and Matter' a scoring chapter, and what should be the preparation strategy?
Yes, 'Magnetism and Matter' is generally considered a highly scoring chapter as it is more theoretical and has fewer complex derivations compared to other chapters. For the CBSE Board Exam 2025-26, a good strategy is to:
- Focus on the definitions and differences between dia-, para-, and ferromagnetic materials.
- Thoroughly understand Earth's magnetic elements and be able to solve simple numericals based on them.
- Practice the conceptual 'why' questions, such as why field lines don't cross or the choice of materials for magnets.
7. What is the underlying reason for diamagnetism, and why do diamagnetic materials move towards weaker magnetic fields?
The fundamental reason for diamagnetism lies in the orbital motion of electrons. According to Lenz's Law, when an external magnetic field is applied to a substance, it induces a magnetic moment in the electrons in a direction opposite to the applied field. This opposing magnetic moment results in a net repulsive force. Because potential energy is minimized when the substance moves against the force, it is pushed from a region of stronger magnetic field to a region of weaker magnetic field to achieve a more stable state.
8. What are the most important formulas from 'Magnetism and Matter' needed to solve expected numerical problems in the board exam?
For numerical problems in the board exams, you should focus on a few key formulas:
- Torque on a bar magnet in a magnetic field: τ = M B sinθ
- Potential energy of a magnetic dipole: U = -M B cosθ
- Relationship between Earth's magnetic elements: BH = B cosδ and BV = B sinδ
- Magnetic field of a bar magnet on its axial line: Baxial = (μ₀/4π) * (2M/r³)
