Transcript Lecture 10
Admin: Mid-term date Friday March 20th. Lab grades posted on Sakai This week’s lab: Special resistors as sensors: thermistors and photoresistors (don’t forget the pre-lab) •Assignments: • • • • • Second assignment complete. Third assignment is posted Due Monday 9th Use the hints. Be careful with the symbolic answers Copyright © 2009 Pearson Education, Inc. Today • Another Kirchhoff example • Mesh analysis Copyright © 2009 Pearson Education, Inc. 1. Label the currents 2. Count the unknowns 3. Apply loop and junction rules 4. Solve the equations Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. Mesh analysis How many unknown currents are there? Copyright © 2009 Pearson Education, Inc. Mesh analysis How many unknown currents are there? Copyright © 2009 Pearson Education, Inc. 6: But mesh analysis reduces this to 3! Mesh Analysis Simple example: 2 meshes (A Mesh is a loop that does not contain other loops) Step 1: Assign mesh currents clockwise Step 2: Apply KVL to each mesh (write the mesh equations) • The self-resistance is the effective resistance of the resistors in series within a mesh. The mutual resistance is the resistance that the mesh has in common with the neighbouring mesh • To write the mesh equation, evaluate the self-resistance, then multiply by the mesh current • Next, subtract the mutual resistance multiplied by the current in the neighbouring mesh for each neighbour. • Equate the above result to the driving voltage: taken to be positive if it tends to push current in the same direction as the assigned mesh current Mesh1: (R1+R2)I1 Mesh2: - R2I2 =ε1-ε2 -R2I1+ (R2+R3)I2 =ε2-ε3 Step 3: solve currents Mesh analysis example