Jasmine Grover Content Strategy Manager
Content Strategy Manager
The property of magnet to attract other substances (some specific substances) is known as Magnetism.
Bar Magnet: The Bar Magnet is a solid bar like three dimensional structure which has one South Pole and has one North Pole to direct the movement.
The Magnetic Field Line:
The magnetic field lines of a magnet (or a solenoid) form continuous closed loops. This is unlike the electric dipole where these field lines begin from a positive charge and end on the negative charge or escape to infinity.
The magnetic field lines do not intersect, for if they did, the direction of the magnetic field would not be unique at the point of intersection.
Read Also: Magnetic Properties of Material
| Table of Content |
Key Terms: Magnetic Dipole, Gauss Law, Electrostatics, Magnetic materials, Magnetic Field, Magnetic moment, Magnitude, Vector
Magnetic Dipole in a Uniform Magnetic field:
[Click Here for Sample Questions]
The torque on the needle is,
τ = m × B ; B = Magnetic Field and m= Magnetic moment
In magnitude τ = mB sinθ
Also Read:
| Related Articles | ||
|---|---|---|
| Magnetism and Matter | Curie's law | Permanent Magnets and Electromagnets |
| Magnetization and Magnetic Intensity | Earth’s Magnetic Field | Ferromagnetism |
Gauss Law
[Click Here for Sample Questions]
Consider a small vector area element \(\bigtriangleup\)S of a closed surface S as.
The magnetic flux through ÄS is defined as \(\bigtriangleup\)φB = B.\(\bigtriangleup\)S, where B is the field at \(\bigtriangleup\)S. We divide S into many small area elements and calculate the individual flux through each. Then, the net flux φB is,
φB= \(\bigtriangleup\)φB=B.\(\bigtriangleup\)S=0
Compare this with the Gauss’s law of electrostatics. The flux through a closed surface in that case is given by ∑ E \(\bigtriangleup\)S = qε0 ; where q is the electric charge enclosed by the surface.
The video below explains this:
Gauss's Law in Magnetism Detailed Video Explanation:
The difference between Gauss’s law of magnetism and that for electrostatics is a reflection of the fact that isolated magnetic poles (also called monopoles) are not known to exist.
- There are no sources or sinks of B; the simplest magnetic element is a dipole or a current loop.
- All magnetic phenomena can be explained in terms of an arrangement of dipoles and/or current loops.
- The net magnetic flux through any closed surface is zero.
Gauss’s law of magnetism states that the flux of B through any closed surface is always zero B.\(\bigtriangleup\)S=0 s. If monopoles existed, the right-hand side would be equal to the monopole (magnetic charge) qm enclosed by S. [Analogous to Gauss’s law of electrostatics,
B.\(\bigtriangleup\)S= μ0qm S where qm is the (monopole) magnetic charge enclosed by S.]
Consider a material placed in an external magnetic field B0. The magnetic intensity is defined as,
H=B0μ0.
The magnetization M of the material is its dipole moment per unit volume. The magnetic field B in the material is, B = µ0 (H + M)
For a linear material M = χ H. So that B = µ H and χ is called the magnetic susceptibility of the material.
Where, χ = The three quantities,
The relative magnetic permeability = µr
The magnetic permeability = µ are related as follow,
µ =μ0 μr
µr = 1+ χ
Magnetic materials are classified as: diamagnetic, paramagnetic, and ferromagnetic.
- For diamagnetic materials, χ is negative and small
- For paramagnetic materials, χ is positive and small.
- Ferromagnetic materials have large χ and are characterized by non-linear relations between B and H. They show the property of hysteresis.
Do check out:
Previous Year Questions
- An electron in motion is associated with… [ KCET 1996]
- Two parallel wires carry electric current in same direction. The wires... [ KCET 1996]
- Resistance of an ideal ammeter is...[ KCET 1996]
- If a current of 0.1 A is passed through the coil, what is the couple acting?...[CBSE Class 12 ]
- The acceleration of the falling magnet is..[NEET]
- A bar magnet is equivalent to ............[KCET 2004]
- A metal ring is held horizontally and bar magnet is dropped through….[NEET]
- The total charge, induced in a conducting loop when it is moved in magnetic field depend on...[NEET 1992]
- If a charge particle enters perpendicular in the uniform magnetic field, then...[JIPMER 2016]
- Who invented the cyclotron?
- When a charged particle moving with velocity is….
- The angle of dip at a place is….
- The associated magnetic moment is given by….
- A uniform electric field and a uniform magnetic field are produced…
- Ampere’s circuital law can be derived from…..
- If a magnetic dipole of moment M situated in the direction of …
- If the susceptibility of dia, para and ferro magnetic materials are ….
- Materials suitable for permanent magnet, must have which of the following properties ?
- At what temperature, the ferromagnetic substances become paramagnetic ?
- a magnetic induction of strength at its centre is...
Sample Questions
Ques. A short bar magnet placed with its axis at 30° with an external field of 800 G experiences a torque of 0.016 Nm. (a) What is the magnetic moment of the magnet? (b) What is the work done in moving it from its most stable to most unstable position? (c) The bar magnet is replaced by a solenoid of cross-sectional area 2 × 10-4 m2 and 1000 turns, but of the same magnetic moment. Determine the current flowing through the solenoid. (5 marks)
Ans: a) We know that ; τ = m B sin θ, θ = 30°, hence sinθ =1/2.
Thus, 0.016 = m × (800 × 10-4 T) × (1/2)
m = 160 × 2/800 = 0.40 A m2
- the most stable position is θ = 0° and the most unstable position is θ = 180°.
Work done is given by
W= Umθ=180-Um(θ=0)
= 2 m B = 2 × 0.40 × 800 × 10-4 = 0.064 J
- ms = NIA. From part (a),
ms = 0.40 A m2 ;
0.40 = 1000 × I × 2 × 10-4;
I = 0.40 × 104 /(1000 × 2) = 2A;
Ques. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why? (1 mark)
Ans: If field lines were entirely confined between two ends of a straight solenoid, the flux through the cross-section at each end would be non-zero. But the flux of field B through any closed surface must always be zero. For a toroid, this difficulty is absent because it has no ‘ends’.
Ques. Magnetic field arises due to charges in motion. Can a system have magnetic moments even though its net charge is zero? (1 mark)
Ans:. The average of the charge in the system may be zero. Yet, the mean of the magnetic moments due to various current loops may not be zero. We will come across such examples in connection with paramagnetic material where atoms have net dipole moment through their net charge is zero.
Ques. What is Earth Magnetic Field? (1 mark)
Ans: Three quantities are desirable to stipulate the magnetic field of the earth surface – the horizontal component, the magnetic declination, and the magnetic dip.
Ques. What is Super-conductor? (1 mark)
Ans: The most exotic diamagnetic materials are superconductors. These metals are cooled to very low temperatures which exhibits both perfect conductivity and perfect diamagnetism. . In this case χ = –1, µr = 0, µ = 0
Ques. What is Meissner Effect? (1 mark)
Ans: The phenomenon of perfect diamagnetism in superconductors is called the Meissner effect.
Ques. Give some common examples of Ferromagnetic material. (1 mark)
Ans: Cobalt, Iron, Nickle, Gadolinium.
For Latest Updates on Upcoming Board Exams, Click Here: https://t.me/class_10_12_board_updates
Do Check Out:
Comments