This lesson introduces Kirchhoff’s rules and focuses on the junction rule, which describes how current behaves where branches meet. It matters because many circuits cannot be reduced to simple series and parallel combinations.
In a simple series circuit, the same current flows through every component. In a simple parallel circuit, components share the same pair of connection points. More complex circuits may contain several branches and junctions, so their resistors may not form clear series or parallel combinations.
All flashcards
What is a junction?
A junction, also called a node, is a point where three or more wires connect.
State Kirchhoff’s junction rule.
The sum of currents entering a junction equals the sum of currents leaving it: ∑Iin=∑Iout.
Why must current balance at a junction?
Current is charge flow. Since charge is conserved and does not continuously accumulate at an ordinary junction, charge flow into the junction must equal charge flow out.
How should you choose an unknown current’s direction?
Choose and draw a direction consistently. A positive result confirms the assumed direction; a negative result means the actual current is opposite.
What makes a junction equation redundant?
It is redundant when it is algebraically equivalent to another equation and therefore adds no independent information.
Quiz questions
What does Kirchhoff’s loop rule require for a complete closed path?Answer: The signed potential changes sum to zero.
When a battery is crossed from its negative terminal to its positive terminal, what voltage change occurs?Answer: A potential rise equal to the battery’s emf.
A resistor is traversed in the direction of its conventional current. What signed voltage change should be used?Answer: A drop of IR.
Two voltage sources are connected in series with their emfs aiding. How does their combined emf compare with the individual emfs?Answer: It equals the sum of their emfs.
For matched solar cells connected in parallel, what happens to the array’s voltage and available current?Answer: Voltage stays approximately the same; available current increases.
Based on University Physics Volume 2 by Samuel J. Ling, William Moebs, Jeff Sanny (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.