# MAGNETIC EFFECT OF CURRENT AND MAGNETISM; NCERT Class 12 Physics Important Questions With Answer pdf

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## MAGNETIC EFFECT OF CURRENT AND MAGNETISM

1. Magnetic Poles: They are centres of attraction near the ends of a magnet.
2. Test of Magnetism Repulsion is the sure test of magnetism.
3. Magnetic Dipole: A magnetic dipole consists of two unlike poles of equal strength and separated by a finite distance.
4. Magnetic Dipole Strength: The quantitative strength of a magnetic pole 1s known as pole strength (m). Unit is A.M.
5. Magnetic Dipole Moment: Magnetic dipole moment is the product of pole strength and magnetic length. So, M=mx21
6. Earth’s Magnetic Elements: Magnetic elements of earth at a place are the quantities which describe completely in magnitude as well as direction of the magnetic field of earth at that place.
7. Magnetic Declination The angle between the magnetic meridian at a place and the geographical meridian at that place is called magnetic declination.
8. Angle of Dipole: Angle of dip at a place is the angle which a freely suspended magnetic needle makes with the horizontal component. It is also known inclination.
9. Neutral Point : It is a point where the field due to magnet is completely neutralised by the horizontal component of earth’s magnetic field.
10. Magnetic Permeability (p): It is the ability of a material to permit the passage of magnetic lines of force through it. or, it is magnetic induction produced in a specimen due to an external magnetising field of unit intensity.
11. Relative Magnetic Permeability (u): For a material it is defined as the ratio of the number of lines of magnetiC induction per unit area (1.e..flux density B) in that material to the number of magnetic lines per unit area that would be present, if the medium were replaced by vacuum, μr=B/B⁰= μ/μ⁰
12. Intensity of Magnetisation : It is the magnetic moment acquired per unit volume. 1=M/V=M×21/A×21=M/A
13. Magnetic Susceptibility (Xm): It is the capability of a substance to acquired magnetism and it is the ratio of the intensity of magnetisation (i) induced in the material to the magnetising force. (H) Applied (Xm) = 1/H
14. Diamagnetic Substances: These are the substances in which the individual atoms/molecules/ions do not possess any net magnetic moment of their own. These substances when placed in a magnetic field, move from stronger to weaker magnetic field, e.g. Bismuth, Antimony, Copper, Gold, Quartz, Mercury, Water, Alcohol, Air, Hydrogen.
15. Paramagnetic Substances : These are the substances in which each individual atom/molecule/ion has a net non-zero magnetic moment of its own. When such a material is placed in an external magnetic field, they move slowly from weaker to stronger magnetic field,
e.g. Aluminium, Platinum, Chromium,Manganese, Crown glass, Copper sulphate,Oxygen etc.
16. Ferromagnetic Substances: These are the substances in which each individual atom/molecule/ion has a non-zero magnetic moment.When placed in an external magnetic field they move rapidly from weaker to stronger magnetic
field. e.g., Fe, CO, Ni, Steel.
17. Magnet: Substance having attractive and directive properties are known as magnets. There are two types of magnet:
(a) Natural Magnet: It has iregular shape and have weak attractive property. For Ex.Magnetite. It is also known as load stone.
(b) Artificial Magnet: It has regular shape and have strong attractive property. For Ex. (1) Bar magnet (ii) Ball ended magnet(iii) Horse shoe shaped magnet (iv) Ring magnet (v) Magnetic needle.
18. Magnetic Meridian : Magnetic meridian at any place is the imaginary vertical plane passing through the magnetic axis of a magnet, freely Suspended at that place.
19. Geographic Meridian: At any place it is the imaginary vertical plane passing through the geographic axis of the earth at that place.
20. Curie’s Law: It states that the magnetic Subceptibility of paramagnetic substance is inversely proportional to the absolute temperature.
21. Magnetic Induction (B): The total magnetic field inside a magnetic material is the sum of the external magnetising field and the additional magnetic field produced due to magnetisation of the material and is called magnetic induction B The magnetic induction may also be defined as the total number of magnetic lines of force crossing per unit area normally through a material.
Mathematically, B= F/m
Its S.I. unit is NA–¹m–¹ or Tesla (T) or
Weber.metre–2 or JA–’m–2
22. Magnetising Field Intensity (H): The ability of magnetising field to magnetise material medium is expressed by a vector H.called magnetising field intensity or magnetic intensity.

Mathematically, H = B⁰/μ⁰
The dimensions of magnetic intensity are[M⁰L–¹T⁰] [A]. S.I. units is ampere. metre–¹ or Am–’ or Nm–²T–¹ or Jm–¹Wb–¹

1. Magnetic Field: The space around a magnet or a current carrying conductor in which the magnetic effects are experienced is called the magnetic field.
2. Magnetic Induction (Magnetic Flux Density) : Magnetic induction or magnetic flux density at a point in a magnetic field is equal to the force acting on a unit charge moving with unit velocity in a direction at right angles to the
direction of magnetic field at the point.The number of lines of induction passing through a unit area placed normal to the lines also measure the magnitude of magnetic induction or magnetic flux density B. Its
Dimension formulae is [ML⁰T–² A–¹].
3. Unit of Magnetic Flux Density:
(a) Unit of B is NA–¹ m–¹ or tesla (T).
(b) Magnetic field induction at a point is said to be one tesla if a charge of 1 coulomb,when moving at right angles to the direction of the magnetic field at that point with the velocity of 1 ms experiences a force of 1N.
(c) 1 tesla =1 Wb m–2
(d) In C.G.S. system the unit of B is gauss.1 tesla = 10 gauss (G).
4. Direction of Magnetic Field: Direction of magnetic field is given by right hand thumb rule.If we hold a wire carrying current in our right hand such that the thumb points along the direction of current the fingers will curl round the wire in the direction of magnetic field around the wire.
5. Force on a charged particle in a Magnetic Field: Charged particle at rest does not a magnetic field. experience any force A charged particle will not experience any force if it is moving parallel to the magnetic field.
6. Motion of a charged particle in a Magnetic Field In this case the magnitude of velocity boil and kinetic energy does not change but the direction of velocity and momentum does change
7. Work done by a Magnetic Force : Magnetic force always does zero work on a charged particle.
8. Cyclotron: Cyclotron is a machine used to accelerate the charged particles.
9. Fleming’s Left hand Rule: Hold the thumb,the fore finger and the middle (central) finger of your left hand mutually at right angles. If the fore finger is pointing in the direction of magnetic field (B), the central finger in the direction of current (TD (or the length of conductor ) then the thumb always indicates the direction of thrust
(or force F) on the conductor.
10. One Ampere: One ampere is the current,which when flowing in two parallel, infinitely long conductors of negligible cross-sectional area placed in vacuum separated by 1m produces between them a force of 2 x 10-7 Nm. Moving Coil Galvanometer: Moving coil
11. galvanometer is an instrument for the detection and measurement of a small current. It is also known as dead beat galvanometer.
12. Ammeter: An ammeter is a moving coil galvanometer with a small resistance (shunt) in at parallel to its coil. It measures current in a circuit.
13. Voltmeter: A voltmeter is a moving coil galvanometer having a high resistance in series with its coil. It measures potential difference between two points in the circuit.
14. Biot-Savart’s Law: This law gives the magnetic field at a point due to a small current element.
Mathematically, dB=μ⁰/4π. Idk.sin∅/r²
15. Lorentz Force: It is the net force experienced by a moving charged particle when both electric and magnetic fields are present.
16. Principle of moving coil Galvanometer When a current carrying coil is placed in a magnetic field, it experiences a torque.
17. Force between two parallel conductor carrying current: Force is attractive in nature if current is flowing in same direction and repulsive in nature if current is flowing in opposite direction.
18. Voltage Sensitivity: It is the deflection produced in a galvanometer when a unit p.d. is applied across it.

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