Batteries use an ongoing chemical reaction to generate a potential difference between two terminals.

Battery – a device that can create electricity using a chemical reaction. It converts energy stored in molecules inside the battery into electricity. They produce direct current (DC) electricity (electricity that flows in one direction, and does not switch back and forth). A battery can provide electricity in areas that do not have electric power distribution.

  • Invisible Engineering – Chemist Angela Belcher looks to manufacture high technology out of viruses using nanotechnology to grow batteries. Batteries that could last weeks or months and be thinner than a credit card.

Capacitors can store charge like a battery, but have no internal chemistry to maintain a potential; however they can discharge very rapidly whereas batteries have a limit on how much current they can output. Once the charge in a capacitor has been used up, it cannot be replenished until the capacitor is charged by an external current. Capacitors have high power density, but low energy density. Batteries have low power density, but high energy density.

The hand battery

To do and notice
Put your left hand on the aluminum plate and your right hand on the copper plate. An electric current flows which you cam observe on the meter.

Try various combination, such as copper and aluminum, copper and copper, etc. in order to get clear indications on the meter you may want to rub the plates with your hands.
Try making you hands moist by breathing on them. Does this have any effect on the meter current?
Try touching the copper and aluminum plates with one finger of each hand at a time, then two fingers, and three, etc.
Have one person put a hand on the copper plTe and another person put one hand on the aluminum plate then join hands together.

What is going on
Your body acts like the acid in a battery. A different chemical reaction takes place when your hand, which is slightly damp and salty, touches the copper plate than when your hand touches the aluminum plate. One of these reactions takes electric charge away from the copper plate, and the other reaction adds charge to the aluminum plate.

The excess electric charge on the aluminum plate then flows through the meter and then back to the copper plate to equalize the charge which is missing there.

What’s the problem?
This battery stretches without losing oomph – Japanese paper craft inspired engineers to create a flexible power source

  • Ask – There are many places where small flexible batteries are needed. What are the limitations with current battery technologies? How could a small flexible battery improve medical devices? Wearable technology?
  • Imagine – Are there examples of something rigid appearing to be flexible or stretchy? How can origami be used? The Muira fold is used solve a similar but different problem.
  • Design, Build – Using three different kirigami patterns as models for their batteries, they produced batteries that stretched without losing power. Best of all, the batteries “could stretch without changing height,” says Jiang.
  • Improve – In the future, flexible batteries could power devices built into everything from clothes to tiny space satellites.

That’s engineering

  • direct current (DC) or “continuous current” – the flow of electricity in a single direction, from the positive to the negative terminals (potential, poles).
  • alternating current (AC) – an electric current of which magnitude and direction vary, unlike direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, because this leads to the most efficient transmission of energy.

Engineering ideas

  • chemical reaction, capacitor, potential difference, current, direct current (DC, alternating current (AC), flow, switch, electricity, discharge, power density, energy, flow, positive, negative, terminals, magnitude, direction, waveform, sine wave, transmission

Do It
Challenges for you to work on…

  • Glow sticks – Watch the video (2:16), then build your own glow stick. You need: 9-volt battery, Battery snap cap, A string of ornamental lights (that can be destroyed), Duct tape or electrical tape, Scissors, Wire strippers