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184_notes:ac [2018/08/09 19:18] – [Voltage Transformer] curdemma184_notes:ac [2021/07/13 13:30] (current) – schram45
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 Section 22.2 in Matter and Interactions (4th edition) Section 22.2 in Matter and Interactions (4th edition)
  
-[[184_notes:changing_e|Next Page: Changing Electric Fields]]+/*[[184_notes:changing_e|Next Page: Changing Electric Fields]]
  
-[[184_notes:b_flux_t|Previous Page: Changing Magnetic Fields with Time]]+[[184_notes:b_flux_t|Previous Page: Changing Magnetic Fields with Time]]*/
  
 ===== Changing Flux from an Alternating Current ===== ===== Changing Flux from an Alternating Current =====
 As we said before, one of the most important sources of a changing magnetic field is an alternating current. This is what actually comes out of the wall outlets; as opposed to the current from a battery which is a constant current (or a direct current). We are only briefly going to talk about alternating current as it refers to induction and changing magnetic flux, but there are many more applications of alternating current, especially with regard to circuits, resistors, and capacitors. For the purposes of these notes, we will talk about how we represent an alternating current, how that alternating current can produce an induced current/potential, and how that applies to voltage transformers. As we said before, one of the most important sources of a changing magnetic field is an alternating current. This is what actually comes out of the wall outlets; as opposed to the current from a battery which is a constant current (or a direct current). We are only briefly going to talk about alternating current as it refers to induction and changing magnetic flux, but there are many more applications of alternating current, especially with regard to circuits, resistors, and capacitors. For the purposes of these notes, we will talk about how we represent an alternating current, how that alternating current can produce an induced current/potential, and how that applies to voltage transformers.
  
-==== Alternating Current ====+===== Alternating Current =====
 [{{  184_notes:Week14_6.png?200|Current over time in an alternating current cycle}}] [{{  184_notes:Week14_6.png?200|Current over time in an alternating current cycle}}]
  
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 This means that a larger period would be related to a smaller frequency, and a smaller period would be related to a higher frequency. Since the period is often easier to think about conceptually, it may be easier to start with period (from a graph for example) and then relate it back to the frequency.    This means that a larger period would be related to a smaller frequency, and a smaller period would be related to a higher frequency. Since the period is often easier to think about conceptually, it may be easier to start with period (from a graph for example) and then relate it back to the frequency.   
  
-==== Voltage Transformer ====+===== Voltage Transformer =====
 If you have an oscillating current, this would also mean that you would have an oscillating magnetic field everywhere around the wire (since currents create magnetic fields). If there is an oscillating magnetic field, this means that there will also be an induced potential/current in any nearby loop of wire since the magnetic field would be constantly changing. One common application of this idea is called a step-up transformer (or alternatively a step-down transformer), which is crucial to getting electricity from the power generator to your house. If you have an oscillating current, this would also mean that you would have an oscillating magnetic field everywhere around the wire (since currents create magnetic fields). If there is an oscillating magnetic field, this means that there will also be an induced potential/current in any nearby loop of wire since the magnetic field would be constantly changing. One common application of this idea is called a step-up transformer (or alternatively a step-down transformer), which is crucial to getting electricity from the power generator to your house.
  
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 To get around this problem, a step up transformer is used to change a low voltage, high current circuit (like what comes out the generator) into a high voltage, low current circuit for transport from the generator to the neighborhoods or wherever it is needed. A step down transformer is then used close to the neighborhoods to return the high voltage, low current back to a low voltage, high current circuit that is then used in your house. You may have seen these around your neighborhood - they look like small boxes attached to the power lines overhead, generally on the lines going from a larger street into a residential area (shown in the figure to the left). To get around this problem, a step up transformer is used to change a low voltage, high current circuit (like what comes out the generator) into a high voltage, low current circuit for transport from the generator to the neighborhoods or wherever it is needed. A step down transformer is then used close to the neighborhoods to return the high voltage, low current back to a low voltage, high current circuit that is then used in your house. You may have seen these around your neighborhood - they look like small boxes attached to the power lines overhead, generally on the lines going from a larger street into a residential area (shown in the figure to the left).
  
-[{{  184_notes:week14_7.png?400|Primary and Secondary solenoids in a transformer}}]+[{{  184_notes:week14_7.png?400|Primary and Secondary solenoids in a step-up transformer}}]
  
 In these notes, we will go through how a step up transformer works and how it uses induction to change the voltage from a low voltage to a high voltage. We will use a basic transformer, which is essentially two solenoids wrapped around a iron ring (shaped like doughnut), as shown in the figure to the right. The first solenoid, which will refer to as the primary solenoid, is connected to the power generator and has the low voltage (and high current). The second solenoid, which we will refer to as the secondary solenoid, should then have a high voltage (and low current) and eventually be connected to the city through a step down transformer.   In these notes, we will go through how a step up transformer works and how it uses induction to change the voltage from a low voltage to a high voltage. We will use a basic transformer, which is essentially two solenoids wrapped around a iron ring (shaped like doughnut), as shown in the figure to the right. The first solenoid, which will refer to as the primary solenoid, is connected to the power generator and has the low voltage (and high current). The second solenoid, which we will refer to as the secondary solenoid, should then have a high voltage (and low current) and eventually be connected to the city through a step down transformer.  
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 ==== Examples ==== ==== Examples ====
-[[:184_notes:examples:Week14_ac_graph|Analyzing an Alternating Current Graph]] +  * [[:184_notes:examples:Week14_ac_graph|Analyzing an Alternating Current Graph]] 
- +  * [[:184_notes:examples:Week14_step_down_transformer|Designing a Step-down Transformer]] 
-[[:184_notes:examples:Week14_step_down_transformer|Designing a Step-down Transformer]]+    * Video Example: Designing a Step-Down Transformer 
 +{{youtube>NAngoOBjCSA?large}}
  
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  • Last modified: 2018/08/09 19:18
  • by curdemma