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Download Faradays Law of Electromagnetic Induction and Lenz`s Law
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Michael Faraday (1791-1867) An English Physicist and Chemist who discovered that electricity can be generated by moving a conductor through a magnetic field or by moving a magnetic field pass a conductor. Magnetic Flux • A measure of the amount of magnetic field lines passing a certain area. • The SI system unit for magnetic flux is a Weber (Wb) or Tm2 (Telsa times meters squared) • Denoted by the capital Greek letter phi, Φ. • Magnetic Flux is a scalar quantity. • Φ=BA cosθ, θ is the angle between the magnetic field and a normal to the plane of the area. A magnetic field of 3.5 T passes through an area of 2.0 m2. How much flux passes through the area given that the field lines passes perpendicular to the plane of the area. Φ = BAcos θ =3.5 T(2.0 m2)cos 0° = 7.0 Webers = 7.0 Wb normal Magnetic flux (field lines) passing thru an area Faraday’s Law of Electromagnetic Induction • A changing magnetic flux induces an EMF (electromotive force/voltage/potential difference) in the area surrounding the flux. EMF voltage N t N = number of turns (loops) of wire Methods to Induce an EMF 1. 2. 3. (B)A EMF voltage t t B( A) EMF voltage t t B( A) B l w EMF voltage Blv t t t Continually changing the magnetic field strength Change the area exposed to a constant magnetic field. Move a conductor with a length, l, exposed to a magnetic field at a velocity, v. Changing the Strength of the Magnetic Field S N Motion towards area Magnet moves closer to area Increasing the flux passing through the conducting area S N Motion away from area Magnet moves farther from area Decreasing the flux passing through the conducting area •A voltage/EMF results in the conducting area and as a result as a current. •The magnetic field change can be achieved by moving a magnetic (steady magnetic field) closer and farther away from the conducting area. Changing the Area Exposed to the Magnetic Field S N Increasing Flux change S S Induced EMF/voltage increased N N Zero flux passing through area Maximum EMF/voltage induced Another Method of Changing the Area Exposed to the Magnetic Field All sides of the wire are exposed Moving the wire will change the flux through the area thus inducing an EMF/voltage in the wire. Moveable exposed wire voltage Another Method of Changing the Magnetic Field Strength and Area Exposed to the Magnetic Field Moving a Conductor Through a Uniform Magnetic Field Δw through field l B v ε = EMF = voltage = Blv sin θ B – magnetic field strength l – length of wire exposed to the magnetic field v – the speed of the area through the magnetic field Θ = angle between velocity direction and magnetic field How an Electrical Generator Works? Generator – a device that converts mechanical energy to electrical energy. Generator Animation Power generation animation Lenz’s Law • The current induced in a conductor by an external magnetic field will always have a magnetic field from the induced current to reduce the change in flux. S N motion Conducting area Which way will the current travel? (clockwise or counterclockwise) Lenz’s Law • The current induced in a conductor by an external magnetic field will always have a magnetic field that opposes the change in magnetic flux causing the induction. I T he magnetic field from the magnetic x x x S I N x x motion x x x x x I The magnetic field in the wire opposing the original magnetic field causing the induction Use the right hand rule on the induced magnetic field to determine the current direction. I x – the opposing magnetic field caused from the induced current. Lenz’s Law • Consider if the opposite occurred. I T he magnetic field from the magnetic x S I N motion What would x I happen? x x x – the opposing x magnetic field cause x from the induced x current. x x x I Hypothetical magnetic field induced in the wire Use the right hand rule on the induced magnetic field to determine the current direction. Lenz’s Law Example motion View direction N S N clockwise What is the pole induced on the right side of the metal bar in the solenoid? What is the direction of the current as viewed towards the right? Modification of Faraday’s Law Due to Lenz’s Law EMF voltage - N t The negative sign takes into account that the voltage opposes the change In flux Electromagnetic Wave • A changing electric field will induce a changing magnetic field. • A changing magnetic field will induce a changing electric field. Electromagnetic field animation Electromagnetic Animation 1 Electromagnetic field Animation 2