11th Physics Notes - Magnetism


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11th Physics Notes - Magnetism

  1. 1. Magnetism Important Terms and Definitions Two types of magnets: - natural and artificial Natural magnets The stones which possess the property to attract other stones are called load-stones. Where load stones are suspended freely, it remained in equilibrium in north-south direction. Magnetic dipole An arrangement of two magnetic poles of equal and opposite strengths separated by a finite distance is called a magnetic dipole or a bar magnet. The two magnetic poles of dipole are called N-pole & S-pole An isolated pole does not exist.
  2. 2. Poles are Fictitious :A bar magnet is assuming to have 2 opposite poles (N & S) situated near its ends. If we try to separate the two poles by cutting the magnet into two pieces, opposite poles are found to appear at the broken ends and each piece is again a new magnet with opposite poles. Even if the magnet is broken to the atomic level, it exists with two poles. This shows that the two poles of a magnet can not be separated from each other. Thus, a single magnetic pole i.e. monopole cannot exist. So, magnetic poles always appear in pairs and hence any magnet is called a dipole and it is said that, a magnetic monopole doesn’t exist or poles of a magnet cannot be separated.
  3. 3. Magnetic length The distance between the two poles of a bar magnet is called the magnetic length of the magnet. It is a vector. Direction S-pole to N-pole Magnetic length = 5/6 (Geom. length)
  4. 4. Note 1. Pole strength (m) The ability of a magnetic pole to produce magnetic field around it is called magnetic pole strength. 2. Axis of a magnetic dipole A straight line passing through magnetic poles of a magnetic dipole is called axis of a magnetic dipole. 3. Equator of a magnetic dipole A straight line passing through the centre of a magnetic dipole and perpendicular to its axis is called equator of a magnetic dipole.
  5. 5. Magnetic dipole moment (M) The product of the strength of either pole and the magnetic length of the magnet is called magnetic dipole moment. Magnitude : M = m × 2ℓ, where m = pole strength of N-pole Direction : S-pole of the magnet to its N- : Ampere meter2 (Am2) pole Unit
  6. 6. Magnetic field The space around a magnet (or a conductor carrying current) in which its magnetic effect can be experienced, is called the magnetic field. The SI unit of strength of magnetic field (also known as magnetic induction or magnetic flux density) is tesla (T) 1 tesla (T) = 1 weba / metre2 = 1 wb/m2 1 tesla (T) = 1 N/Am........ {B = F/m, which is the B due to a role strength} 10-4 tesla (T) = 1 gauss (G)
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