magnetic induction in physics world presentation

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1. TOPIC: electromagnetic induction

2. CONTENTS: Introduction Principle Faraday’s Experiment Magnetic Flux Faraday’s 1 st Law Of Induction Faraday’s 2 nd Law Of Induction Lenz’s Law Motional EMF Inductance Self Inductance Mutual Inductance Applications

3. INTRODUCTION The word electromagnetic induction is made up of two words electromagnet + induction. An electromagnet is a type of magnet in which the magnetic field is produced by electric current. The magnetic field disappears when the current is turned off. The process of generating current in a conductor by placing the conductor in a changing magnetic field is call induction. So electromagnetic induction is the production of a potential difference across a conductor when it is exposed to a varying magnetic field. It refers to the phenomenon where an emf is induced when the magnetic flux linking a conductor change.

4. PRINCIPLE Electromagnetic induction is a process where a conductor placed in a changing magnetic field causes the production of a voltage across the conductor. This process of electromagnetic induction, in turn, causes an electrical current, it is said to induce the current.

5. FARADAY’S EXPERIMENT Michael faraday performed series of experiment and based on the results he gave law on induction. Magnetic field is capable of producing current in a conductor. Faraday took a coil and attached a galvanometer to it. As there is no battery attached therefore there is no source of current. He brought the magnet near the coil. When the magnet is moved towards the coil galvanometer showed deflection. Galvanometer even showed the deflection in the opposite direction when the magnet is taken away from the coil. When magnet was not moved there was no deflection in the galvanometer. Faster the magnet is moved the more is the deflection in the galvanometer. This showed more and more current flows if the magnet is moved verry fast.

6. This shows current is related to magnet; Same effect was observed if the coil is moved and the magnet was not moved. From this experiment, faraday concluded that whenever there is relative motion between a conductor and magnetic field, the flux linkage with a coil changes and this change in flux induces a voltage across a coil.

7. MAGNETIC FLUX Magnetic flux  is defined as the number of magnetic field lines passing through a given closed surface. It provides the measurement of the total magnetic field that passes through a given surface area. Here, the area under consideration can be of any size and under any orientation with respect to the direction of the magnetic field. Magnetic flux symbol: Φ or Φ B . Φ B = B.A = BA cosθ The SI unit of magnetic flux is  Weber (Wb). The CGS unit is  Maxwell.

8. FARADAY’S LAW OF ELECTROMAGNETIC INDUCTION Faraday’s Laws of Electromagnetic Induction consists of two laws. The first law describes the induction of emf in a conductor and the second law quantifies the emf produced in the conductor. FARADAY’S FIRST LAW OF ELECTROMAGNETIC INDUCTION The discovery and understanding of electromagnetic induction are based on a long series of experiments carried out by Faraday and Henry. From the experimental observations, Faraday concluded that an emf is induced when the magnetic flux across the coil changes with time. Therefore, Faraday’s first law of electromagnetic induction states the following: Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced. If the conductor circuit is closed, a current is induced, which is called induced current.

9. FARADAY’S SECOND LAW OF ELECTROMAGNETIC INDUCTION Faraday’s second law of electromagnetic induction states that; The induced emf in a coil is equal to the rate of change of flux linkage. The flux linkage is the product of the number of turns in the coil and the flux associated with the coil. The formula of Faraday’s law is given below: ε = -N   Where ε is the electromotive force, Φ is the magnetic flux, and N is the number of turns. LENZ’S LAW The German physicist Heinrich Friedrich Lenz deduced a rule known as Lenz’s law that describes the polarity of the induced emf. Lenz’s law states that “The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.” The negative sign in the formula represents this effect. Thus, the negative sign indicates that the direction of the induced emf and the change in the direction of magnetic fields have opposite signs.

10. MOTIONAL EMF The emf induced in a conducting rod when it moves in a region of magnetic field is known as motional emf. Either showing translator motion or rotatory motions, whenever a conducting rod is moving in a magnetic field, a potential difference is established at the ends of the rod. Directed from the high potential end to the low potential, an electric field appears along with the length of the rod. This EMF is called motional emf. Motional emf is calculated by using the formula: E= vBl. Where l denotes the length of the rod, B denotes the magnetic field, and the velocity of the rod perpendicular to the length of the rod is denoted by v. INDUCTANCE Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. L is used to represent the inductance, and Henry is the  SI unit of inductance . 1 Henry is defined as the amount of inductance required to produce an emf of 1 volt in a conductor when the current change in the conductor is at the rate of 1 Ampere per second.

11. SELF INDUCTANCE When there is a change in the current or magnetic flux of the coil, an  electromotive force  is induced. This phenomenon is termed Self Inductance. When the current starts flowing through the coil at any instant, it is found that, that the magnetic flux becomes directly proportional to the current passing through the circuit. The relation is given as: Φ = L*I Where L is termed as the self-inductance of the coil or the coefficient of self-inductance, the self-inductance depends on the cross-sectional area, the permeability of the material, and the number of turns in the coil. The rate of change of magnetic flux in the coil is given as, e = - = - = - L  

12. Self Inductance Formula L= N   Where, L is the self inductance in Henries N is the number of turns Φ is the magnetic flux I is the current in amperes MUTUAL INDUCTANCE Consider two coils: P – coil (Primary coil) and S – coil (Secondary coil). A battery and a key are connected to the P-coil, whereas a galvanometer is connected across the S-coil. When there is a change in the current or  magnetic flux  linked with the two coils, an opposing electromotive force is produced across each coil, and this phenomenon is termed Mutual Inductance.

13. This phenomenon is given by the relation: Φ = MI Where M is termed as the mutual inductance of the two coils or the coefficient of the mutual inductance of the two coils. The rate of change of magnetic flux in the coil is given as, e = - = - = - M Mutual Inductance Formula, M = Where, μ  is the permeability of free space μ r  is the relative permeability of the soft iron core N is the number of turns in coil A is the cross-sectional area in m 2 l is the length of the coil in m