CHAPTER AT A GLANCE
1. Introduction: In 1820, Hans Christian Oersted discovered that a compass needle got deflected when an electric current passed through a metallic wire placed nearby. This observation relates electricity and magnetism.
2. Magnetic field: When metals like iron, nickel or cobalt are placed near a magnet, they are attracted towards the magnet. Beyond this region, they won’t be attracted towards the magnet. It means every magnet has a region around it, in which it’s force (attraction or repulsion) can be experienced. This region is known as magnetic field.
3. Magnetic lines of force (or magnetic field lines): The path (straight or curved) along which unit north pole moves in a magnetic field (if it is free to do so) is called magnetic lines of force. They are imaginary lines.
4. Types of magnetic fields:
(i) Uniform magnetic field: The magnetic field is said to be uniform ifits magnitude is equal and direction is same at every point in the space.
(ii) Non-uniform magnetic field: The magnetic field is said to be non-uniform if its magnitude is not equal and direction is not same at every point in space.
5. Right hand thumb rule: According to this rule, if we imagine that we are holding a wire carrying current and thumb is stretched in the direction of current then the direction in which fingers will be wrapped gives the direction of magnetic lines of force. It means if the current is flowing in the upward direction then the direction of magnetic lines of force will be anticlockwise and if current is flowing in the downward direction then the direction of field will be clockwise.
6.Factors on which strength of magnetic field around a straight wire carrying current depends
- Strength of this magnetic field depends on current i.e., it is directly propotional to the current flowing through the conductor.
- Distance from the wire: Strength of the magnetic field is inversely proportional to the distance from the wire carrying current.
7. Clock rule: It is applicable for circular loops. If the current flowing appears to be in anticlockwise direction in any circular loop, then this face acts as north pole of the magnet. While if the current flowing appears to be in clockwise direction in a circular loop, then this face acts as south pole of the magnet.
8. Solenoid: A solenoid is a coil of many turns of an insulated wire closely wound in the shape of a tight spring.
9. Factors on which magnetic field due to a solenoid depends
- The number of turns of the wire forming a solenoid. (Magnetie field) B an
- The strength of current Bal
- Nature of material inside the solenoid; B aµ (whereµ is permeability of material).
10. Electromagnet: It is a piece of magnetic material like soft iron or hard steel which is placed inside a solenoid through which current is flowing. There are two types of electromagnet:
(i) Permanent electromagnet: It is a type of electromagnet which is obtained by placing magnetic material like hard steel in the strong magnetic field produced by a coil.
(ii) Temporary electromagnet: It behaves like a magnet till the current flows through it, i.e., it stops behaving like a magnet when the flow of current is stopped. It is obtained by placing soft iron in a coil through which current is flowing.
Uses of electromagnets
- They are used to lift heavy iron pieces.
- They are used in many devices like electric bell, electric horn, telephone receiver etc.
Force exerted on a wire carrying current placed in a magnetic field: It was discovered that when a magnetic needle is placed near a conductor carrying current, it shows deflection i.e. a force exerted on it.
11. Fleming’s left hand rule: According to this rule, stretch thumb, fore finger and central finger of left hand in such a way that these fingers are perpendicular to each other. If fore finger is placed in the direction of magnetic field and middle finger in direction of current, then thumb will point towards the direction of force.
12. Electric motor – DC motor: It is a device which is used to convert electrical energy into mechanical energy.
13. Fleming’s right hand rule: According to Fleming’s right hand rule, stretch thumb, fore finger and middle finger in such a way that these three fingers are perpendicular to each other. Now adjust thumb and fore finger in such a way that thumb indicates the direction of the motion of the conductor and the fore finger indicates the direction of magnetic field, then the direction in which middle finger points is the direction of flow of current.
14. Electromagnetic induction: Michael Faraday discovered that when a
conductor moves in a magnetic field, current is generated in the conductor. This phenomenon of production of electric current is known as electro magnetic induction and the current so obtained is called induced current.
15. Galvanometer: A galvanometer is an instrument that can detect the presence ofa current in a circuit.
- D.C. electric generator: It is a type of generator which is used to produce induced current which forms in one direction (unidirectional called Direct Current).
- A.C. generator: It generates alternating current (a.c.) that changes its polarity after every halfrotation.
17. Household circuit: We receive supply of electric power through mains. One of the wire in the supply has red insulation called live wire. Another wire with black insulation is called neutral wire. Potential difference between them is 220volt.
18. Short circuit: It occurs when the insulation of wires get damaged and live and neutral wires touch each other.
19. Over-loading: When large number of electric appliances of high power rating are switched on at the same time, large amount of current is drawn in the circuit due to which copper wire gets heated which may lead to fire.
20. Fuse: Fuse is a safety device having a very thin wire which is made up of either tin or alloy of tin and lead (or tin and copper). This wire has low melting point so it melts and breaks the circuit easily if the current in the circuit exceeds it’s safety valve, due to short circuit or over loading.
- Class 10 Notes
- Class 10 Science Notes
- NCERT Solutions for class 10th Science Chapter 13 Magnetic Effects of Current