Download AC vs. DC

Electricity at Home
Read the following note and complete the questions at the end of the note.
AC vs. DC
There are two types of current electricity:
1. Direct Current (DC): electrons in a circuit travel only in one direction (from the negative terminal to the positive terminal.
Ex. Battery
2. Alternating Current (AC)­ electrons move back and forth, but there is no net movement of electrons in either direction.
Ex. Outlet in wall
Batteries produce a Direct Current. Alternating Current comes out of our outlets. An appliance which can run off a battery requires an ADAPTOR if it can also be plugged into an outlet. The adaptor converts _____ to _____ .
Why do we have an AC current?
Answer­ Electricity can be generated as either AC or DC, but AC allows us to change the Voltage ­ Current ratio in order to save money (This cannot be done with DC).
The full explanation...
­ Electricity has to travel a long distance through wires to reach your home
­ To transmit the electrical energy without losing energy to heat, requires a low current (I) and a high voltage (V). ­ When the electricity reaches your home, the voltage is too high and the current is too low for your appliances.
­ As the wires reach neighbourhoods, the electricity is "transformed" again to a lower voltage and a higher current before eventually entering our homes at 110 V. ­ The greenboxes in the streets are called transformers
­ These transformers lower the voltage before they enter the home.
­ Transformers cannot change the voltage of DC which is an advantage of using AC.
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In the home
To prevent damage to appliances or dangerous situations the following devices are used.
Fuses ­ are thin strips of metal placed in appliances which melt, breaking the circuit if the current gets too large ­ preventing damage to the appliance itself. Circuit breakers are similar but instead of melting, they flip over if the current gets too large.
Large currents create heat which might cause electrical fires.
GFI stands for Ground Fault Interrupter and is designed to detect currents of a few milliamperes and trip a breaker at the receptacle or at the breaker panel to remove the shock hazard.
Homework
Answer the following questions on a separate piece of paper using full sentences.
1. Name 3 electrical devices in your home that have adaptors (look for the adaptor box on the cord or plug). What does this adaptor do? Use the note to help you explain your answer.
2. Why do we use AC to power our homes instead of DC? Explain your answer fully providing a detailed explanation.
3. What is the scientific name for the "green box" on your street. What does this green box do? 4. Does your home have fuses or a circuit breaker (ask an adult at home about this). How does this device help protect your home?
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