^Dip (δ) & Horizontal component

The vertical component of the Earth’s magnetic field points downwards in the northern hemisphere. If the magnetic needle of a dip circle is perfectly balanced about a horizontal axis so that it dips (moves down) in a vertical plane of the magnetic meridian and aligns. Itself at some angle to horizontal at which are parallel, this angle is known as the angle of dip (also known as inclination).

We can say that angle of dip at a place in the magnetic meridian is the angle between horizontal component of earth’s magnetic field (H) & its resultant intensity (B) or it is the angle made by the axis of a freely suspended magnet with the horizontal line. e.g. Dip angle = 42⁰  at Delhi.

In figure shown, the resultant magnetic field is in the magnetic meridian, d is angle of dip, B_H and B_V denote horizontal and vertical components of Earth’s magnetic field respectively.

B_H = B cosδ, B_V = Bsinδ

Exactly at the equator the Earth’s magnetic field is parallel to the Earth’s surface, angle of dip & vertical component of Earth’s magnetic field are zero, thus a freely suspended magnet will be horizontal at the equator. Exactly at the centre of poles the Earth’s magnetic field is normal to the surface of the Earth, angle of dip is 90⁰ and the horizontal component of the Earth’s magnetic field is zero. Therefore a freely suspended magnet will become vertical at the poles.

Superconductors: Perfect diamagnetics

For super conductors cooled to very low temperatures χ = –1 & μ_r = 0.

Thus the super conductors are perfect diamagnetic materials. The phenomenon of perfect diamagnetism in superconductors is calledthe Meissner effect. In superconductors the field lines are completely expelled. Also a superconductor repels a magnet and (by Newton’s third law) is repelled by the magnet.

Superconducting magnets can be used in variety of situations, for example, for running magnetically levitated super fast trains.

Magnetic lines prefer to pass through air than through a diamagnetic material & through a ferromagnetic material than through air.

Oersted observation

Oersted (1820) was the first to discover magnetic field associated with a current carrying conductor. He found that if a wire carrying a current from South to North is placed Over a magnetic needle, then the north pole the needle gets deflected towards the West. This is named as SNOW rule.

Facts

• If the liberated mass doesn’t react with electrodes, the electrode is called inert otherwise soluble.
• Cu – anode with any metallic cathode in Cu –voltameter forms inert electrode.
• Platinum electrodes in water voltameter, Platinum anode in Cu – voltameter are the examples of inert electrodes.
• During electrolysis mass of cathode increases, (Reduction takes place at cathode) while that of anode decreases & concentration of electrolyte remains constant.
• Alternating current can’t be used in electrolysis. As the frequency of AC changes periodically, so there will be no deposition on any electrode actually.
• The back EMF or polarization EMF in water is 1.5 V. This is why to carry out electrolysis of H₂O we need a voltage greater than 1.5 V.
• Electrolysis is useful in, electroplating, extraction of metals from ores & their purification, electrolytic etching to mark logo, to produce H₂ and O₂ commercially, to separate non-metallic particles from the metallic ones, to ascertain the polarity of a battery, in finding equivalent weights & atomic weights.