* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download File
Neutron magnetic moment wikipedia , lookup
Geomagnetic storm wikipedia , lookup
Magnetometer wikipedia , lookup
Maxwell's equations wikipedia , lookup
Electrical resistance and conductance wikipedia , lookup
Magnetic monopole wikipedia , lookup
Giant magnetoresistance wikipedia , lookup
Earth's magnetic field wikipedia , lookup
Mathematical descriptions of the electromagnetic field wikipedia , lookup
Magnetotactic bacteria wikipedia , lookup
Superconducting magnet wikipedia , lookup
Alternating current wikipedia , lookup
Lorentz force wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Electromagnetism wikipedia , lookup
Skin effect wikipedia , lookup
Electromotive force wikipedia , lookup
Earthing system wikipedia , lookup
Force between magnets wikipedia , lookup
Magnetochemistry wikipedia , lookup
Magnetoreception wikipedia , lookup
Electromagnetic field wikipedia , lookup
History of electrochemistry wikipedia , lookup
Magnetohydrodynamics wikipedia , lookup
Electromagnet wikipedia , lookup
Multiferroics wikipedia , lookup
Electricity wikipedia , lookup
Ferromagnetism wikipedia , lookup
Magnetotellurics wikipedia , lookup
CBSE-X Session: 2011 – 2012 MAGNETIC EFFECTS OF ELECTRIC CURRENT Magnetic Effects of Current (i) H.C. Oersted: He first proposed experimentally that a magnetic field is developed around a current carrying conductor. He showed it by deflection of a magnetic needle placed near a closed circuit, having current. (ii) Maxwell cork-screw rule or right hand thumb rule: According to this rule imagine yourself holding a current carrying conductor in your right hand such that thumb points in the direction of flow of current then the fingers wrapping around it gives the direction of flow of magnetic field. (iii) Fleming Left hand Rule: Stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other. If the forefinger shows the direction of the magnetic field and the central finger that of the current, then the thumb will point towards the direction of motion of the conductor. (iv) Fleming’s Right Hand Rule: Stretch out the forefinger, the middle finger and the thumb of the right hand such that these are mutually perpendicular to each other. If the forefinger shows the direction of the magnetic field, thumb shows the direction of motion of the conductor then the middle finger gives the direction of current produced in the conductor (Induced current). ELECTRIC MOTOR AND ELECTROMAGNETIC INDUCTION An electric motor is a device for converting electric energy into mechanical energy. Thus, an electric motor is the reverse of an electric generator. There are two types of electric motors: (i) AC motor (ii) DC motor. Principle of Electric motor: When a conductor or rectangular coil carrying current is placed in between a magnet, the conductor experiences a force and moves. Thus, its converts electric energy to mechanical energy. Electric Generator: A device which converts mechanical energy into electrical energy is called an electric generator. Principle of Electric generator – Electromagnetic induction: When a conductor/rectangular coil is kept in between a magnet and when there is a relative motion between them, there is a change in magnetic flux and thus current is induced. Thus, a generator changes mechanical energy to electrical energy. PREPARED BY: ADITYA SHRIVASTAVA 1 Call: 9889107785 Reasons of short-circuiting Short-circuiting happens due to : (a) Damage to the insulation of the power-lines (b) A fault in an electric appliance due to which current does not pass through it. Consequences of short-circuiting On account of short-circuiting, resistance of the circuit decreases to a very small value and consequently the current becomes very large. This large current results in heating of live wires, which produces sparking at the point of short-circuiting. This sparking sometimes causes fire in a building. (Apart from short-circuiting, the increase in current in the circuit and consequent heating may also be due to overloading of the circuit). Electric Fuse: A Safety Device An electric fuse is a device, which is used in series to limit the current in an electric circuit so that it easily melts due to overheating when excessive current passes through it. A fuse is a wire of a material with very low melting point. Electric fuse can avoid incidents like electric shock, fire, damage to an electric appliance due to : Short-circuiting or Overloading (withdrawing current beyond a specified limit) in a circuit. Earthing Many electric appliances of daily use like electric press, toaster, refrigerator, table fan etc. have a metallic body. If the insulation of any of these appliances melts and makes contact with the metallic casing, the person touching it is likely to receive a severe electric shock. This is due to the reason that the metallic casing will be at the same potential as the applied one. Obviously, the electric current will flow through the body of the person who touches the appliance. To avoid such serious accidents, the metal casing of the electric appliance is earthed. Since the earth does not offer any resistance, the current flows to the earth through the earth wire instead of flowing through the body of the person. More over, due to very low resistance (almost nil) offered by the earth wire, the current in the circuit rises to a very high value, thereby melting fuse in that circuit and cutting off its electric supply. Role of Magnetism in Medicine and Organisms In our body, small electric current travels along the nerve cells due to ions. This current produces a very weak magnetic field (about one billionth time weaker than the Earth's magnetic field) in our body. Heart and brain are the two main organs in our body where this magnetic field is quite significant. The magnetic field in our body enables us to obtain the images of its different parts by using a technique called MRI (Magnetic Resonance Imaging). On analysing the images obtained through MRI, we are able to make a medical diagnosis, e.g., location and size of a tumour in brain etc. Thus, magnetism plays an important role in modern medical science. Apart from this, there are certain organisms, which have the ability to sense Earth's magnetic field and travel from one place to another. For example, some types of fishes are able to detect magnetic field by using special receptors whereas in certain organisms, crystals of magnetite enable to move along the Earth's magnetic field. PREPARED BY: ADITYA SHRIVASTAVA 2 Call: 9889107785 MIND MAP Magnetic field is a space around magnet where force of attraction and repulsion is detected. Magnetic field lines represent a magnetic field. a The lines are directed from North pole to South pole. b They are parallel and equidistant to each other and form closed and continuous curve. Oersted demonstrated that around every conductor carrying an electric current there is a magnetic field. The magnitude of magnetic field is (B) B NI r Unit of magnetic field is Tesla. Electro magnetic induction is the conversion of mechanical energy into electrical energy. Electric motor is used to convert electric energy into mechanical energy. Generator is used to convert mechanical energy into electrical energy. MAGNETIC EFFECTS OF ELECTRIC CURRENT A magnet is a substance with attractive and directive properties. Visit us at: http://www.intangiblepoint.webs.com PREPARED BY: ADITYA SHRIVASTAVA Right hand thumb rule – Imagine a straight conductor in your right hand such that the thumb points in the direction of current and the curling of fingers gives the direction of magnetic field lines. Fleming left hand rule – On stretching your left hand, fore finger points in the direction of the magnetic field, the central finger points in the direction of current and the thumb points in the direction of motion of conductor. Fleming right hand rule – On stretching your right hand, such that the central finger and the first finger are mutually perpendicular to each other, the first finger points in the direction of magnetic field, the thumb points in the direction of motion of the conductor and the central finger points in the direction of induced current. The cable supplying power to house hold has a Live wire (red). b Neutral wire (black) c Earth wire (green) A fuse protects the electric circuits and appliances from short circuiting or from overloading. Call at: +91- 9889107785 3 Call: 9889107785