Voltage, Series/Parallel Circuits, and Multimeter Basics

Voltage and Elevation in Circuits

The speaker uses an elevation metaphor for voltage: the battery elevates the electrons to a higher potential (nine volts in the example).
As you move around the circuit, the voltage level stays at 9 V until you pass through a resistive element (the squiggles).
The only places where voltage changes (drops) occur are across the squiggles (the resistors). If you move through wires with no resistance, there is no voltage change (in an ideal wire).
Pipe-flow analogy: voltage difference acts like pressure that drives water (electrons) through the circuit; tilt or pushing on the pipe is analogous to providing voltage.
The bigger the voltage, the more the electrons want to move; voltage is the driving force behind current.
In a 9 V circuit, you can think of the path as starting at 9 V, moving through resistors (voltage drops occur here), and ending at 0 V after returning to the battery.

In a loop with a battery and resistors, the voltage drop occurs across the resistors, not across the ideal wires.
Example sketch idea from the talk: between points a and b there may be no drop (still 9 V); between b and c there is a drop; between c and d there is the remainder drop to ground (0 V).
The total drop around the loop equals the battery’s emf (9 V in this example) when you sum all the resistor drops: V_{total drops} = ext{emf} = 9 ext{ V}.
The speaker notes that formulas for these drops will be learned next week, but the qualitative idea is: resistors are where the energy is dissipated (as heat, light, etc.).

Series circuits:
- The same current flows through every component: $$I1 = I2 = \