Direct current (DC)

In a DC (direct current) circuit where the electricity flows in one direction, we can think of a battery as a storage tank like the water tower in your neighborhood. If nobody turned on their faucet, the water in the tower would just sit there. Forever. Physicists like to think of this as "potential energy." Like a boulder at the top of a hill, it will just sit there, forever, until someone pushes it over the hill or an earthquake shakes it from the top of the hill or erosion undermines it starting it to roll down the hill. When the boulder is rolling down the hill, physicists like to think of this as kinetic energy. So, the water will just sit in the top of the water tower until you turn on the faucet to your water hose.

AC, DC: What's The Difference ?

The difference between alternating current (AC) and direct current (DC) is readily explained, yet most widely published "explanations" seem to muddle the facts and cause confusion.  I hope that this short article may help to clarify matters a little.

A Little Etymology

Originally, alternating current was called "alternate" current and direct current was called "continuous" current.

Computer memory works on the basis of electrons that are moved around and stored. Electrons are small and, when it comes to insuring that information will not be lost over time, can be difficult to control using relatively thick insulator walls, so that information will not be lost over time.

The physics issues limit storage density and cost the system a great deal of energy so researchers pursue nanoelectronic components that make use of ions, i.e. charged atoms, for storing data. Ions are some thousands of times heavier that electrons and are therefore much easier to 'hold down'. In this way, the individual storage elements can almost be reduced to atomic dimensions, which enormously improves the storage density. 

When many of us were kids, water-transfer printing meant a fake tattoo. For our children, it will mean peel-and-stick versions of solar cells that charge cell phones, change the tint on windows, or power their toys. 

Peel-and-stick, or water-assisted transfer printing (WTP), technologies were developed by a group at Stanford and have been used before for nanowire based electronics. A new partnership between Stanford University and the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) has conducted the first successful demonstration using actual thin film solar cells, NREL principal scientist Qi Wang said.

Researchers have designed a new kind of adaptive material with tunable transparency and wettability features - imagine a tent that blocks light on a dry and sunny day, and becomes transparent and water-repellent on a dim, rainy day. Or highly precise, self-adjusting contact lenses that also clean themselves. 

The new material was inspired by natural dynamic, self-restoring systems, such as the liquid film that coats your eyes - tears. Individual tears join up to form a dynamic liquid film with an obviously significant optical function that maintains clarity, while keeping the eye moist, protecting it against dust and bacteria, and helping to transport away any wastes – doing all of this and more in literally the blink of an eye. 

An autonomous robotic jellyfish the size and weight of a grown man has been developed. 

Nicknamed Cyro, this prototype is a larger model of the robotic jellyfish (named RoboJelly) the same team unveiled in 2012. RoboJelly is roughly the size of a man's hand, typical of jellyfish found along beaches.

A team of Harvard scientists have succeeding in measuring the magnetic charge of single particles of matter and antimatter more accurately, by capturing individual protons and antiprotons in a "trap" created by electric and magnetic fields and precisely measuring the oscillations of each particle.

The researchers were able to measure the magnetism of a proton more than 1,000 times more accurately than an antiproton had been measured before. Similar tests with antiprotons produced a 680-fold increase in accuracy in the size of the magnet in an antiproton.    

Terahertz (THz) radiation, in the electromagnetic spectrum between microwaves and infrared light, is rapidly finding important uses in medical diagnostics, security, and scientific research. 

But researchers are pursuing answers regarding potential human health risks. 

Wind energy is not very efficient and activists have turned on it because 300,000 out of 10,000,000,000 birds are killed by wind turbines each year. Without subsidies it would not exist but exist it does, only now manufacturers have had to discover physics they did not anticipate.

Wind turbine failures primarily happen because components are weakened under turbulent air flow conditions and then need to be replaced, at significant cost.

Researchers at the Universities of Edinburgh and Southampton have brought the science of repairing broken bones into the 21st century, using adult bone stem cells combined with a degradable lightweight plastic  that encourages real bone to re-grow.