Electrical Safety

• The voltage in a standard U.S. wall outlet is approximately 110V

• Many electrical appliances can not handle that many volts.

  • ​Computer speakers 9 V

  • Projections TV 15000 V

  • Phone charger 5 V

• A transformer changes the voltage for the appliance.​

Tansformers

• A primary coil creates a magnetic field in the iron core.

• Since the current in the coil is AC, the B-field is always changing.

• The iron makes the B-field go through the secondary coil.

• The changing B-filed means the flux in the secondary coil is also changing and thus induces an emf.​

1. Induced emf

2. Primary emf

3. Dividing

4. Transformer equation

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But P = IV...

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Transformers

Transformers

• A transformer that steps up the voltage, steps down current and vise versa.

• To keep electrical lines from getting too hot, the electrical companies use transformers to step up the voltage up to 11000V. The box on the electrical pole is a transformer that steps the voltage down to 220V. ​

Electrical Safety

• A standard electrical plug in the U.S. has:

  • Two grounds

    • ​White wire

      • Wide prong

      • Return through ground

    • ​Green wire

      • 3rd prong

      • Grounds the case​

  • "Hot" wire

    • Black/red

      • Carries the higher voltage​

Electrical Safety

• Circuit Breaker

  • If the current load gets too large, an electromagnet pulls a switch to stop the current

  • Stops wires from getting hot in short circuits that lead to fires.​

• Ground Fault Interrupter (GFCI)

• Both ​sides (hot and neutral) are wrapped around a metal toroid like transformer, but the number of loops are equal.

• Normally the induced current is 0 since the two sides cancel.

• If an imbalance occurs (like current going through a person and into the ground), an electromagnet pulls a switch​

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Electrical Safety