Electromagnetism Objectives Magnets and Magnetic Field EM Induction

Electromagnetism Objectives: • • Magnets and Magnetic Field EM Induction and Generators AC Currents Transformers

Magnets and Magnetic Field Lines Two Poles: North and South Same poles repel Opposite poles attract Magnetic Field Lines Outside: From North to South Inside: From South to North Magnetic Field: B measured in Tesla [T]

Earth’s Magnetic Field Van Allen Belts Protect us from the Solar Radiation On Earth’s Surface B ≈ 0. 0005 T

What Creates the Magnetic Field Electric Currents create Magnetic Fields Question: Why do we use coaxial cables? A: The magnetic field cancels outside!

Electromagnetic Induction Electric Current can be induced if the amount of magnetic field lines through the coil changes with time

Mutual Induction The changing electric current in one coil leads to changes in the amount of magnetic field lines through the secondary coil. The resultant change in the amount of magnetic field lines in the secondary coil lead to induced currents there Question: Where have you seen This principle in action? A. Induction stoves?

Generators and Motors Maximum Induced EMF (in Volts) depends on: • Number of Turns, N • Area of coil, A • Magnetic Field, B • Angular speed, ω EMF = N A B ω

Generators and Motors Question: How much is the max induced EMF in Volts • Number of Turns, N = 100 • Area of coil, A = 0. 0025 m 2 • Magnetic Field, B = 0. 005 T • Angular speed, ω = 1 rpm EMF = N A B ω ω = 30 rpm ≈ 3. 14 rad/s EMF = (100) (0. 0025) (0. 05) (3. 14) = 0. 004 V = 4 m. V

Alternating Currents Effective (RMS) Current and Voltage Ieffective = 0. 707 Imax Veffective = 0. 707 Vmax Question: How much is the max voltage in the European Union where the effective (rms) voltage is 220 V?

Transformers EMFsecondary EMFprimary = Nsecondary Nprimary Step-up Transformers Question: A Nsecondary Nprimary

20 P 1. How much max. EMF can you induced by rotating a coil at 100 rpm, that has an area of 0. 05 m 2 and 100 turns, in the presence of 0. 05 T magnetic field? Ans. P 2. If you triple the number of turns and double the area of a coil, by what factor will you increase the induced EMF? (everything else kept the same) Ans. P 3. The 110 V-value of the current in the US outlets is actually the effective voltage. What is the actual maximum voltage? Ans. P 3. A step-up transformer has 30 turns on its primary coil and 300 turns on its secondary. If plugged into 110 Volts, what will be the voltage on the secondary coil? Ans.