Stump the Scientist: AC vs DC power flow
Happy New Year everybody! As we enter 2012, we promise to answer more questions for you this year than we have in any year past. Keep them coming and we’ll do our best to keep the answers flowing!
Question submitted by GE Facebook fan Nakul Narayanan:
What is the difference between AC and DC power flow?
Response from Chief Scientist Jim Bray:
The difference between AC and DC power flow is denoted by the difference between its letters: A=alternating, and D=direct. C= current. First of all, the current C stands for the electric current in a wire, and this current consists of electrons that are being pushed through the wire by an electric field, also known as a voltage. “Power flow” means that the current carries power or energy to something (e.g., a computer, TV, motor, radio) to which the wire is attached. “Alternating” means that the current, or electrons, are being pushed back and forth by the voltage, while “direct” means that the electrons are being push only in one direction all the time by the voltage.
Why can both alternating and direct current give a power flow to something? You can consider an analogy. Think of holding a rope tightly in your hand. If someone pulls it though you hand in one direction, it will heat up your hand, maybe enough to burn you (“rope burn”). But also, if that person pulls the rope back and forth through your hand, it will also heat up and maybe burn your hand. Similarly, both AC and DC current can deliver power or energy to equipment.
In electrical engineering, we use both AC and DC power. Most of the electrical transmission that you see on outdoor power lines and in your home is AC because it has some advantages in manipulating it compared to DC. The frequency of alternation in the US is 60 cycles per second (called Hertz), but some other countries use 50 Hertz.
A question for ‘Stump the Scientist’!
Consider the sport of curling – when you slide a curling rock down a sheet of ice with a clockwise rotation, the rock will move laterally to the right. If you slide the same curling rock down a linoleum floor with the same clockwise rotation, it will move laterally to the left. Why does the curling rock behave differently on these two surfaces?