# Negative Voltage

by Jaymo3141
Tags: negative, voltage
 P: 12 Ok, I am starting to understand what voltage is. But i'm sort of confused when it comes to negative voltage. I know that voltage is defined as potential energy per unit charge. I understand it as analogous to "pressure". I don't understand what it means to have negative voltage though. How can "pressure" or even energy be negative?
 HW Helper P: 7,134 The sign convention for potential (voltage) is positive for a field from a positive charge, and negative for a field from a negative charge. In the case of a circuit, a point on the circuit with negative voltage means the potential is negative compared to a "neutral" ground.
 P: 3,154 Voltage is a relative quantity. Pressure isn't allways a good analogy for voltage because pressure is an absolute quantity. Consider a 9V battery. The voltage on the +ve terminal is 9V with respect to the -ve terminal. However it's equally true to say that the -ve terminal is at -9V relative to the +ve terminal. You cannot just say that the +ve terminal is at 9V without citing what the reference voltage is. Frequently we are lazy and don't allways bother to cite what the reference is on circuit diagrams. Sometimes we write a small foot note which says "All voltages are measured with respect to...". Consider the circuit below. What is the voltage on Node A relative to node B? What is the voltage on Node A relative to the 0V node? What is the voltage on Node B relative to 0V node? What would you write on the circuit diagram? Attached Thumbnails