Which of the following symbols represents a DC voltage source in a circuit schematic?

• A. A circle with a $+$ and $-$ sign inside
• B. A zigzag line
• C. A rectangle with a diagonal line through it
• D. A pair of parallel lines of unequal length, such as $\left|\right|$

Answer: (D)

Verified step by step guidance

1. Understand that in circuit schematics, different symbols represent different electrical components.
2. Recognize that a DC voltage source is typically represented by a pair of parallel lines of unequal length, where the longer line indicates the positive terminal and the shorter line indicates the negative terminal.
3. Identify that a circle with a plus and minus sign inside usually represents a battery or a voltage source but is less standard than the parallel lines symbol for a DC source.
4. Know that a zigzag line represents a resistor, which opposes current flow, not a voltage source.
5. Understand that a rectangle with a diagonal line through it is often used to represent a fuse or a different component, not a DC voltage source.