Kirchoff’s Laws

Question 1

Kirchhoff’s 1st Law (current)

Answer 1

The algebraic sum of the currents entering and leaving a junction is zero

Question 2

Kirchhoff’s 2nd Law (voltage)

Answer 2

The algebraic sum of the potential differences and EMFs around any closed circuit is zero

Question 3

In any closed loop the sum of the voltage drops is equal to…

Answer 3

The sum of EMFs:
E - V = IR

Question 4

What is the difference between a capacitance and inductance

Answer 4

Capacitance

• Stores energy (electric field) between two plates separated by a dielectric material
• resists sudden changes in voltage by storing or releasing charge
• Behavior: Blocks DC, passes high-frequency AC.

Inductance

• Stores energy in the form of a magnetic field
• resists changes to current by inducing an opposing voltage (back emf)
• Behavior: Allows DC, blocks high-frequency AC.

Question 5

What are passive and active circuit elements

Answer 5

• Passive elements can only control energy already in the circuit (resistors, capacitors, inductors, etc)
• Active elements can generate or amplify energy (transistors, operational amplifiers, diodes, batteries, etc)

Question 6

Resistors in series

Answer 6

• R1 - R2 - …

R = R1 + R2 + …
I = constant

Question 7

Resistors in parallel

Answer 7

• R1 -
• R2 -
• … -

1/R = 1/R1 + 1/R2 + …
I = I1 + I2 + …
V = constant