 # Do Now (2/10/14) An airplane traveling at 750 km/h passes over a region where the Earth’s magnetic field is 4.5 x 10 -5 T. What is the voltage induced.

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Do Now (2/10/14) An airplane traveling at 750 km/h passes over a region where the Earth’s magnetic field is 4.5 x 10 -5 T. What is the voltage induced between the plane’s wing tips if they are 85m apart?.796 V

To the Lab!!! Room 127, get in groups of 3-4

Do Now (2/11/14) What did we observe yesterday when we moved the magnet through the loop? ◦Did changing the number of loops make a difference? ◦What about the speed that you moved the magnet?

Magnetic flux – the magnetic field through an area Units: T*m 2 Tesla per meter squared

Practice!!! A circular loop of wire has a radius of.324m. It is in a uniform magnetic field of.89 T. What is the flux through the loop if it’s plane is perpendicular to the field?

What causes an induced EMF? A wire moving with respect to a magnetic field The EMF (ε) is measured in volts and depends on: ε = B l v Where l is the length of the wire. Remember this?

Faraday’s Law Induced EMF with coils or loops ◦N = number of coils/loops of wire

If ε is proportional to the change in flux, how do I calculate that?

Classwork Use the rest of class time to work on your homework. ‘Electromagnetic Induction’ or ‘Faraday’s Law’

Do Now (2/12/14) Describe Flux in your own words. What is Faraday’s Law?

How is power/energy transported from power plants to our homes, schools, and businesses?

The Transformer A transformer is a device that uses induction and ac current to step voltages up or down. A transformer is a device that uses induction and ac current to step voltages up or down. R a.c. N primary N secondary Transformer InputOutput

Transformers (Continued): R a.c. NpNp NsNs Transformer Recognizing that  /  t is the same in each coil, we divide first relation by second and obtain: The transformer equation: This is the ratio of turns or coils:

Example 7: A generator produces 10 A at 600 V. The primary coil in a transformer has 20 turns. How many secondary turns are needed to step up the voltage to 2400 V? R a.c. NpNp NsNs I = 10 A; ε p = 600 V ε S = 2400 V 20 turns Applying the transformer equation: N S = 80 turns This is a step-up transformer; reversing coils will make it a step-down transformer.

Practice A transformer has an output voltage of 8V when connected to a 120V power-supply. What is the turns ratio of the transformer? 15:1 Ratio Is this a step-down or step-up transformer? Step-up increases VoltageStep-down decreases Voltage

Classwork Use the rest of class time to work on your homework. ‘Faraday’s Law’ or ‘Transformers’

Exit Question:

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