EMF from Magnets Wire sliding through a uniform

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EMF from Magnets • Wire sliding through a uniform magnetic field F v q

EMF from Magnets • Wire sliding through a uniform magnetic field F v q • The wire contains charges q which feel a force due to magnetic field • The charges, if they are moving, undergo work a

EMF from Magnets II v b • Force is caused by cutting across magnetic

EMF from Magnets II v b • Force is caused by cutting across magnetic fields a

Faraday’s Law 10 5 T 3 m/s 2 m 10 m As the bar

Faraday’s Law 10 5 T 3 m/s 2 m 10 m As the bar moves a current is induced! There are no batteries anywhere, so we say that a current is induced, by an induced emf. Hence, an electric current can be induced in a circuit by a changing magnetic field, in the opposite direction to the change in flux.

Faraday’s Law 10 5 T 10 m What is the current induced in this

Faraday’s Law 10 5 T 10 m What is the current induced in this circuit? A) 30 A B) 3 A C) 10 A D) 6 A 3 m/s 2 m

Changing the Flux 1) Change the field within the coil 2) Changing the area

Changing the Flux 1) Change the field within the coil 2) Changing the area of the coil (the explanation we did) 3) Changing the angle between the field and the coil (common method)

Lenz’s Law • EMF causes current in opposite direction compared to right-hand rule •

Lenz’s Law • EMF causes current in opposite direction compared to right-hand rule • Current produces a magnetic field according to the right-hand rule • Current appears in the loop that tries to maintain constant magnetic field • Consider a conducting ring in a magnetic field • Suddenly, the magnetic field is reduced • This causes current to start flowing • Current recreates magnetic field Arises from conservation of energy!

Voltage, Current, and Power 10 5 T 3 m/s 10 m E = va.

Voltage, Current, and Power 10 5 T 3 m/s 10 m E = va. B = 30 V • What is voltage? I = V/R = E/R = 3 A • What is current? • What is power P = I V = I E = 90 W consumed by resistor? • What is force on wire due F = BIL = 30 N to the magnetic field? P = Fv = 90 W • What is power needed to move wire? 2 m

Faraday and Changing the Flux The circuit shown is in a uniform magnetic field

Faraday and Changing the Flux The circuit shown is in a uniform magnetic field that is into the page and is decreasing in magnitude at the rate 150 T/s. The current in the circuit is: V=IR=> I=0. 4 A without considering the field. The current flows counterclockwuse Apply Faraday’s law: the changing flux is: (0. 12)(-150), so the Emf is 2. 2 V, produces an opposed current of 0. 22 A. So the total current is 0. 18 A