Tiêu đề 1. OLYMPIAD M.F. VOL-2 WS(1-76).pdf ✅

X – Physics (Vol–II) Olympiad Class Work Book CONCEPT FLOW CHART
Olympiad Class Work Book X – Physics (Vol–II) Born: 14 August 1777 Died: 9 March 1851 (Copenhagen, Denmark) Known for: Discovery of Electromagnetism and Aluminium Electromagnetism was discovered in the spring of 1820 by the Danish physicist Hans Christian Oersted when, during a lecture to an advanced group of students, he demonstrated that the needle of a compass moved when placed near a cur- rent- carrying wire. By July of that year, he was certain that an electric current produced about it a circular magnetic field, and he published his results in a short paper, written in Latin, and carried by the major scientific journals of Eu- rope. Oersted's great discovery had an enormous impact on the scientific world. More than a hundred scientists published their comments and researches on electro- magnetism within seven years of the discovery, and Oersted was showered with honors and awards. The Royal Society of London gave him the Copley Medal, and the French Academy awarded him a prize of 3000 gold francs. For the rest of his life, he was a recognized leader in science, and in his honor the Oersted was chosen as the standard CGS unit of magnetic field intensity. HANS CHRISTIAN OERSTED
X – Physics (Vol–II) Olympiad Class Work Book ELECTRO MAGNETISM Introduction to magnetism: Magnetic oxide of iron, a naturally occurring iron ore, was found in the district of magnesia Asia Minor in Greece. Hence this ore was called Magnetite. The Greek philosopher, Thales of Miletus, observed that naturally occurring ore of iron attracted small pieces of iron, steel, cobalt, nickel etc., This phenomenon of attraction of iron ore was called magnetism. When a small piece of the iron ore was suspended, it always aligned itself along the north-south direction due to directional property. Because of the directional property the substance was called “lodestone” or “leading stone”. The Chinese and Europeans were known to have used lodestone as a navigational aid. William Gilbert showed that the earth was a huge magnet. It is due to earth’s magnetism that a freely suspended magnetic needle always points in north-south direction. Today we find magnets and magnetic material also in ATM and Credit cards, audio headsets, computers etc., the properties of magnetic materials can be traced back to their atoms and electrons. Magnet: A piece of substance which possesses the property of attracting small piece of iron towards it is called a magnet. Note: When a bar magnet is suspended at its middle and free to rotate in the horizontal plane it always comes to equilibrium in a fixed direction. N A S B North pole South pole up down N S W E One end of a magnet say A is directed approximately towards north and the other end is say B approximately towards south. This observation is made everywhere on the earth. Due to this reason the end A points towards north direction is called north pole and the other end B which points towards south direction is called south pole. They can be marked as N, S as shown in the figure.
Olympiad Class Work Book X – Physics (Vol–II) N A (1) (2) l g lm S B South pole Magnetic Length = 2R Geometric Length = R North pole 2R Where m is the magnetic length of the magnet, g  is the geometrical length or end to end length and m is slightly less than g  . N and S are not located exactly at the ends of the magnet. For calculation purpose we can assume m m g g 5 (actually ) 6       Magnetic field: Around a magnet at all points, the effect of magnet is felt. When another magnet is brought into this space, a force acts on it. The space surrounding a magnet in which its effect is felt is called magnetic field region. If magnetic material like iron or nickel is placed in that space of the field a magnetic induction force acts on it. Thus a magnetic field can also be defined as that which can exert a magnetic force and can produce magnetic induction in the matter placed in it. The magnetic induction as the force acting on unit pole placed at that point. Magnetic field lines of force: The magnetic field of magnet can be mapped by drawing magnetic lines of force. The concept of magnetic lines of force has been developed to visualise the nature (whether the field is uniform or not) and to estimate the intensity of the magnetic field at different points in a region surrounded by a magnet. The path in which a free unit north pole would tend to move in a magnetic field is known as a magnetic line of force (or) simply magnetic “field line”. Since isolated magnetic pole does not exist, a small magnetic needle is used to plot the magnetic line of force. The magnetic lines of force around a bar magnet can be traced using a magnetic needle as shown in the figure. N S Magnetic line of force with magnetic needle