Ch. 5 AC and DC

Question Answer
What are two reasons why we use AC (alternating current)? 1. easy to change voltage– therefore good for long distance delivery, 2. magnetic induction by AC to drive motor
What are three advantages of DC (direct current)? 1. easy to be stabilized at low voltage, 2. low noise- good for electronic devices, 3. easy storage
Typically, electricity that you get in batteries is (direct/alternating) current? direct
True or Flase- With alternating current, the polarity of the voltage between the poles is always changing TRUE
In Canada, how often does this polarity alerternate per second? 60/second
If you measure the voltage of a powerline in Canada, what will you see? 60 Hz sine wave
Why do we need to change the voltage for long distance delivery? In order to increase power we either need to increase the voltage or the current– or BOTH. if we use more current through power line (more heat that will be wasted). If we increase voltage- can keep current small (reduce waste). We want to transfer
Why do we need to change the voltage for long distance delivery?…Cont'd If we want to transfer energy through small village safely– need to transform to lower voltage– safer use. Insulation can be broken at higher voltage. Higher voltage is efficient but not safe for long distance delivery.
In order to increase current we can (increase/decrease) wire/line size. increase
Why is DC low noise? no voltage change– less noise
What are the components/lines of a power outlet for an AC supplier? (3) 1. neutral, 2. Hot, 3. Ground
What is the voltage of the neutral component? 0 Volts
What is the voltage of the hot component? voltage change between -120 to 120 V
What part of the line gives the voltage? hotline
How does current normally travel in an AC power line? across hot and neutral lines– should not be any current going to the grounding
Which of the three components is a safety component? The grounding
The grounding produces a (low/high) resistance pathway for current that is leaking from the hot-neutral low resistance pathway
The resistance of the grounding pathway should be (higher/lower) than the bodies resistance lower
What may change this? What will occur? if body is wet… or standing on wet ground– pathway of body will have lower resistance– increased chance of electric shock
What is used to prevent short circuits (e.g., in home)? a fuse
How does grounding reduce noise? provides a pathway for noise– noise will be short circuited to the grounding
What is the relationship between voltage and insulation? with greater voltage we require increased insulation
What do we use an isolator for in electrical equipment (e.g., equipment connected to patients)? We use the isolator to separate the high voltage part from the low voltage part that may make contact with the human body

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