Electricity and Energy Conversions

• Energy is the ability to do work, and it appears in many forms.
• Electrical devices change electric energy into other forms of energy like light and heat.
• Some technology transforms heat, light, and kinetic energy into electrical energy.

Electricity Conversions

• Many devices convert electrical energy into other forms.
• Equipment can also convert other forms of energy into electricity.
• An activity involves listing devices that convert electrical energy and determining their energy conversion types.

Electricity and Heat

• Electric energy converts to heat in appliances like stoves and hair driers when moving charges meet resistance in a metal conductor.
• Heat can be converted directly to electric energy via a thermocouple, which is a loop of two wires made of different metals joined at both ends.
• Heating one junction of a thermocouple produces a small electric current, which increases with temperature difference.
• If the hot and cold junctions are reversed, the current flows in the opposite direction.
• Thomas Johann Seebeck discovered the basic principle of the thermocouple in 1821, known as the Seebeck Effect.
• Copper and constantan, or iron and constantan, are common metals in industrial thermocouples.
• Thermocouples produce a small amount of current but are used for accurate temperature measurements.

Thermo-electric Generators

• Thermo-electric generators convert heat directly into electricity using thermocouples.
• A thermopile, which connects several thermocouples in a series, creates a potential difference.
• They are reliable, low-maintenance devices used in remote locations to generate limited electrical energy.
• The generator's hot side generally maintains a temperature of 540°C, while the cold side is kept at 140°C.
• Individual thermo-electric generators range from 15–550 W and can be combined to produce up to 5000 W.

Electricity to Motion

• Sound is produced in devices via the piezoelectric effect, where electric current causes vibrations in a tiny crystal.
• When a piezoelectric crystal, such as quartz, connects to a potential difference, it expands or contracts slightly.
• The link between electricity and pressure was first investigated in 1880 by Pierre and Jacques Curie.
• Modern researchers have developed non-crystalline materials that move in response to an electric current, with uses like robotic hands.
• Bar-Cohen's experimental device can lift only 10 g but is inexpensive, durable, and light.

Motion to Electricity

• Barbecue spark lighters use the piezoelectric effect in reverse, generating a potential difference when a piezoelectric crystal is compressed or pulled.
• Devices like crystal microphones and pressure sensors use the changing voltage from a piezoelectric crystal to control electric currents in amplifiers and recording gear.
• The piezoelectric effect can be observed when certain types of crystals produce flashes of light when struck together.

Electricity to Light

• In incandescent light bulbs, a filament glows when an electric current passes through it.
• Fluorescent or neon bulbs produce light when an electric current causes a gas or vapor to glow.
• Piezoelectric crystals produce light when hit together.
• Light-emitting diodes (LEDs) use a fraction of the power of traditional bulbs and last for years.
• The heart of the LED is a tiny semiconductor chip protected by a transparent plastic case.
• Unlike regular light bulbs, LEDs only work when connected correctly in one direction.

Light to Electricity

• Light is an increasingly vital method to produce electricity.
• Photovoltaic cells are made of semiconducting materials such as silicon.
• When light strikes the cell, some light is absorbed, breaking electrons loose and allowing them to flow freely.
• Metal contacts on the top and bottom of the PV cell allow this electric current to be drawn off for external use.
• Solar cells are combined to form modules and arrays to overcome the limitations of voltage and current in individual cells.