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Electrical Safety. Closed circuit. Open circuit. Electrical Safety. Fuse : a short piece of metal that melts if current exceeds a set value (to protect device) Circuit breaker : an automatic switch that opens the circuit when current exceeds a set value. (uses a bimetallic strip).

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Closed circuit

Open circuit

electrical safety1
Electrical Safety
  • Fuse: a short piece of metal that melts if current exceeds a set value (to protect device)
  • Circuit breaker: an automatic switch that opens the circuit when current exceeds a set value. (uses a bimetallic strip)
Ground-fault circuit interrupter: opens a circuit if the current going into a device is not the same as the current coming out of the device.
  • gfci
Short Circuit- a circuit that is formed when wires touch. This effectively shortens the path of the circuit because the current no longer passes through the resistor. The extremely low resistance in the circuit produces very high current, which could cause melt down and fire.
Ground wire: provides a “safety valve” – an additional pathway for charges in case of high current
light bulbs power i 2 r
Light bulbs Power = I2R

The brightness (Watts) of a light bulb depends on both the current going through the bulb and the resistance of the bulb filament.

Which one has a greater influence on the brightness- the current or the resistance?

Thicker wires can carry more current.

Thinner wires have more resistance.

So, which bulb has a thicker filament- a 40 W or a 100 W?

Diode- allows only one direction of current to pass through it.
  • Light emitting diode, LED

As electrons pass through these “semiconductors”, light is emitted

  • Transistors are devices that are often used to amplify small signals into a larger one.
alternating current ac
Alternating Current, AC

The electricity in your houses is alternating current, AC, not direct current, DC – as in batteries.

The main reason for this is that transformers can only step up or step down the voltage if it is alternating current.

Without transformers, there would be great loss of electrical power between the power stations and your houses. For electricity to be very efficient, there would have to be a power generating plant in EVERY community!

Alternating current means that the voltage pushes back and forth, not just one direction.

The electrons just wiggle back and forth.

In the US, they wiggle back and forth 60 times every second.

In other words, the frequency is 60 Hz.

The first use of alternating current in the US was at the Chicago World’s Fair, in 1893, where Nicholas Tesla’s alternating current circuits were chosen instead of direct current, which was backed by Thomas Edison and his General Electric Company.
Tesla Coil
  • Alternating current
  • Systems for wireless communication (radios, remote controls)
  • robotics
  • electrotherapy
  • wireless transfer of electricity
  • x-ray tubes
  • arc lights
  • concepts for electric vehicles
  • devices for lightning protection
  • concepts for vertical takeoff aircraft

Ferris designed and built the first 264 foot (80 meter) wheel for the World's Columbian Exposition in Chicago, Illinois in 1893. This first wheel was 26 stories tall and could carry 2,160 persons. There were 36 cars accommodating 60 people each (40 seated, 20 standing). It took 20 minutes for the wheel to make two revolutions - the first to make six stops to allow passengers to exit and enter; the 2nd a single non-stop revolution - and for that, the ticket holder paid 50 cents. The wheel was moved twice after the 1893 Fair and was eventually disassembled in 1906.