1. Magnetic Field Generator: Toroid

2. Example: Force Between Parallel Currents Four long wires are parallel to each other, their cross sections forming the corners of a square with side a = 20 cm. A 20 A current exists in each wire and is out of the page. What is the force per unit length (magnitude and direction) on any of wire. B1B1 a 12 3 4 B3B3 B2B2 B F

3. Magnetic Induction: Generating Electricity 1. A current appears only if there is relative motion. 2.Fast motion produces a greater current. 3. Clockwise/counter clockwise current with north pole move in/out. Opposite with south pole. Induced current in secondary coil, if there is change of current in the primary coil: switch or ac current Transformer

4. Faraday’s Law of Induction Electric Flux through area AMagnetic flux through area A Amount of electric (magnetic) field passes through an area A Faraday’s Law of Induction: An emf is induced in a loop when the magnetic flux that pass through the loop is changing. The the loop is conducting, then a current will flow. For uniform B: (Weber, or Wb, or T m 2 For a loop with N turns: Change B (change current)Change AChange angle between them