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Magnetic Effect Of Electric Current

Home > Study Notes > Magnetic Effect Of Electric Current
Published in: Physics
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CBSE Class 10 Physics - Chapter 13

Rami M / Dubai

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  1. MAGNETIC EFFECT OF ELECTRIC CURRENT Q) What is a magnet? A) Magnet is an object that attracts objects made of iron, cobalt and nickle. Magnet comes to rest in North — South direction, when suspended freely. Q) What are the uses of magnet? A) Use of Magnets: Magnets are used • in refrigerators. • in radio and stereo speakers. • in audio and video cassette players. • in children's toys and; • on hard discs and floppies of computers. Q) Properties of Magnet? • A free suspended magnet always points towards the north and south direction. • The pole of a magnet which points toward north direction is called north pole or north-seeking. • The pole of a magnet which points toward south direction is called south pole or south seeking. • Like poles of magnets repel each other while unlike poles of magnets attract each other. Q) Magnetic field and field lines: The influence of force surrounding a magnet is called magnetic field. In the magnetic field, the force exerted by a magnet can be detected using a compass or any other magnet.
  2. The magnetic field is represented by magnetic field lines. The imaginary lines of magnetic field around a magnet are called field line or field line of magnet. When iron fillings are allowed to settle around a bar magnet, they get arranged in a pattern which mimicks the magnetic field lines. Field line of a magnet can also be detected using a compass. Magnetic field is a vector quantity, i.e. it has both direction and magnitude. Q) Direction of field line: Outside the magnet, the direction of magnetic field line is taken from North pole to South Pole. Inside the magnet, the direction of magnetic field line is taken from South pole to North pole. Q) Properties of magnetic field lines: (i) They do not intersect each other. (ii) It is taken by convention that magnetic field lines emerge from North pole and merge at the South pole. Inside the magnet, their direction is from South pole to North pole. Therefore magnetic field lines are closed curves.
  3. Magnetic field lines due to current a current carrying straight conductor A current carrying straight conductor has magnetic field in the form of concentric circles, around it. Magnetic field of current carrying straight conductor can be shown by magnetic field lines. The direction of magnetic field through a current carrying conductor depends upon the direction of flow electric current. Current Field c Let a current carrying conductor be suspended vertically and the electric current is flowing from south to north. In this case, the direction of magnetic field will be anticlockwise. If the current is flowing from north to south, the direction of magnetic field will be clockwise. The direction of magnetic field, in relation to direction of electric current through a straight conductor can be depicted by using the Right Hand Thumb Rule. It is also known as Maxwell's Corkscrew Rule. Right-Hand Thumb Rule: f a current carrying conductor is held by right hand, keeping the thumb straight and if the direction of electric current is in the direction of thumb, then the direction of wrapping of other fingers will show the direction of magnetic field.
  4. Current Magnetic Field Maxwell's Corkscrew rule: As per Maxwell's Corkscrew Rule, if the direction of forward movement of screw shows the direction of the current, then the direction of rotation of screw shows the direction of magnetic field. Direc tion magnetic Field Direction of Magnetic field due to a current in a Solenoid: Solenoid is the coil with many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. A current carrying solenoid produces similar pattern of magnetic field as a bar magnet. One end of solenoid behaves as the north pole and another end behaves as the south pole.
  5. Magnetic field lines are parallel inside the solenoid, similar to a bar magnet, which shows that magnetic field is same at all points inside the solenoid. Figure 13.10 Field lines ofthe magnetic field thmugh and around a current canying solenoid. Properties of magnetic field The magnitude of magnetic field increases with increase in electric current and decreases with decrease in electric current. The magnitude of magnetic field produced by electric current decreases with increase in distance and vice — versa. The size of concentric circles of magnetic field lines increases with distance from the conductor, which shows that magnetic field decreases with distance. Magnetic field lines are always parallel to each other. • No two field lines cross each other. Magnetic field lines due to a current through a circular loop In case of a circular current carrying conductor, the magnetic field is
  6. produced in the same manner as it is in case of a straight current carrying conductor. Circular coil ard board Iron Filings In case of a circular current carrying conductor, the magnetic field lines would be in the form of iron concentric circles around every part of the FllmSs periphery of the conductor. Since, magnetic field lines tend to remain closer when near to the conductor, so the magnetic field would be stronger near the periphery of the loop. On the other hand, the magnetic field lines would be distant from each other when we move towards the centre of the current carrying loop. Finally, at the centre, the arcs of big circles would appear as a straight line. Magnetic field and number of turns of coil: Magnitude of magnetic field gets summed up with increase in the number of turns of coil. If there are 'n' turns of coil, magnitude of magnetic field will be 'n' times of magnetic field in case of a single turn of coil.
  7. The strength of the magnetic field at the centre of the loop(coil) depends on . (i) The radius of the coil: The strength of the magnetic field is inversely proportional to the radius of the coil. If the radius increases, the magnetic strength at the centre decreases (ii) The number of turns in the coil : As the number of turns in the coil increase, the magnetic strength at the centre increases, because the current in each circular turn is having the same direction, thus, the field due to each turn adds up. (iii) The strength of the current flowing in the coil: As the strength of the current increases, the strength of three magnetic fields also increases. Electromagnet: An electromagnet consists of a long coil of insulated copper wire wrapped on a soft iron. Magnet formed by producing magnetic field inside a solenoid is called electromagnet. Coil Of insulated wire Soft iron S Cååttery• Key H Bar type Force on a current carrying conductor in a magnetic field: A current carrying conductor exerts a force when a magnet is placed in its vicinity.
  8. Similarly, a magnet also exerts equal and opposite force on the current carrying conductor. This was suggested by Marie Ampere, a French Physicist and considered as founder of science of electromagnetism. The direction of force over the conductor gets reversed with the change in direction of flow of electric current. It is observed that the magnitude of force is highest when the direction of current is at right angles to the magnetic field. Fleming's Left-Hand Rule: If the direction of electric current is perpendicular to the magnetic field, the direction of force is also perpendicular to both of them. The Fleming's Left Hand Rule states that if the left hand is stretched in a way that the index finger, the middle finger and the thumb are in mutually perpendicular directions, then the index finger and middle finger of a stretched left hand show the direction of magnetic field and direction of electric current respectively and the thumb shows the direction of motion or force acting on the conductor. The directions of electric current, magnetic field and force are similar to three mutually perpendicular axes, i.e. x, y, and z-axes. Many devices, such as electric motor, electric generator, loudspeaker, etc.
  9. work on Fleming's Left Hand Rule. Field c Electric motor: A device that converts electrical energy to mechanical energy. It is of two types : AC and DC Motor. Electrical energy is converted into mechanical energy by using and electric motor. Electric motor works on the basis of rule suggested by Marie Ampere and Fleming's Left Hand Rule. Principle of Electric Motor
  10. When a rectangular coil is placed in a magnetic field and a current is passed through it, force acts on the coil, which rotates it continuously. With the rotation of the coil, the shaft attached to it also rotates. s Split rings (P and 9) x Bru shes (X and Y) Axle Figure 13.15 A simple electric motor Construction: It consists of the following parts : Armature: It is a rectangular coil (ABCD) which is suspended between the two poles of a magnetic field. The electric supply to the coil is connected with a commutator. • Commutator or Split — ring: Commutator is a device which reverses the direction of flow of electric current through a circuit. It is two halves of the same metallic ring. Magnet: Magnetic field is supplied bv a permanent magnet NS. Sliding contacts or Brushes Q which are fixed. • Battery: These are consists of few cells.

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