Week 8

Electricity and Magnetism  Chap 8,9

Sensors and Motors are often based on electronics and magnetism

 Electricity magnetism E&M is a complex fundamental interaction.  This interaction  is responsible for most of the features we experience in our world. Basis for atoms and molecules. Determines material properties and interactions. Most phenomena (excluding gravity, falling and earth-sun-moon binding) can be seen as an E&M interaction. 2 charges +,- N,S Electron è - , point particle Protonè + ,  made of quarks No individual N or S poles found Due to electric currents drops with distance act along line joining charges like repel, unlike attract r=distance between charges = unit vector it shows direction only  = provides magnitude of force, sign + means repulsion, neg means attraction Same characteristics as electric force only for N,S poles

While originally the interactions in the columns appeared similar they were considered to be distinct, unrelated interactions.  However, the forces were linked when electric currents were found to have magnetic interactions (electromagnet).

 Electric current Measured in Amps   A Flow Amount of charge that passes through an imaginary slice in a wire per second 1 A = 1 C/s Analogs: water flows in rivers  (flowè amount passes by per second Flow of cars on highway (flowè # cars pass under bridge per second Therefore flow depends on two quantities speed, amount Few cars traveling fast = high flow Many cars traveling slow  high flow Flow at 2:00 AM (90 MPH) i.e. the # under the bridge in a given time can be the same as the flow for a traffic jam (1 MPH). Mississippi can have slow moving sections where the river is wide and faster sections where the river is narrow but the flow is the same.

 Voltage Push that causes the flow Analog: For rivers flow is due to gravity  è  Flowing down hill Analog: For  skiers its due to gravity (vertical drop) Analog: Gravity can be used to propel material along a path the amount of push can be related to the height h. In trying to understand voltage we can consider things that flow down hill due to gravity. We can also identify the height that a skier descends or a river traverses as an important factor in determining flow.  Indeed we can imagine that voltage can be directly linked to the height for a system that has material flowing due to gravity.  This link allows us to develop some intuition about voltage and voltage distribution in a circuit.

Thursday -----------------------------

Fields

E&M film on Maxwell’s equations

Thursday

Hand back the test.