Check logic for Watts calculation

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Discussion Overview

The discussion revolves around the calculation of power generated by a coil when a magnet passes by it, specifically focusing on the logic behind converting wattage into a rate over time. Participants explore the implications of measuring voltage versus power and the assumptions involved in the calculations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant claims to generate 0.05 watts every time a magnet passes the coil and attempts to calculate the total power generated over time based on the frequency of passes.
  • Another participant points out that watts is a rate (J/sec) and that "watts per hour" is not a valid unit, suggesting that energy should be calculated in joules or watt-hours instead.
  • A third participant questions the measurement method, asking for clarification on whether the voltmeter measures power or voltage, and emphasizes the need for a known load to accurately determine power output.
  • Further, a participant suggests that if the power was indeed measured at 0.05 watts, the duration of that power generation must be specified to calculate average power correctly.
  • Another participant provides a formula for electromotive force (E.M.F.) and discusses the conditions under which the measured voltage could be achieved, indicating that the speed and size of the magnet are critical factors.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the initial calculations and the interpretation of measurements. There is no consensus on the correct approach to calculating the power generated or the implications of the measurements taken.

Contextual Notes

Participants highlight limitations related to the assumptions made about the measurement conditions, the nature of the voltmeter used, and the need for additional information about the load to accurately assess power generation.

hobbyist5342
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Thanks to anyone kind enough to help check my logic. Using 13 gauge copper wire and a magnet I can generate .05 watt every time the magnet passes the coil (according to the voltmeter). Am I correct in assuming that if the magnet passes the coil 60 times a minute, then (.05 watts X 60rpm X 60 min/hr) = 180 watts per hour?

Much appreciate your help.
 
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Hi.
Watts is already a rate: J/sec. There is no such unit as "watts per hour". You need to multiply by the duration of the passes to get energy in joules or watt-hours.
 
hobbyist5342 said:
Thanks to anyone kind enough to help check my logic. Using 13 gauge copper wire and a magnet I can generate .05 watt every time the magnet passes the coil (according to the voltmeter). Am I correct in assuming that if the magnet passes the coil 60 times a minute, then (.05 watts X 60rpm X 60 min/hr) = 180 watts per hour?

Much appreciate your help.
What voltmeter do you have that measures power (Watts)? Can you post a picture or say what the model number is?
 
hobbyist5342 said:
Using 13 gauge copper wire and a magnet I can generate .05 watt every time the magnet passes the coil (according to the voltmeter).

Did you mean "0.05 Volts" ? In which case what you probably got was some sort of pulse that might be displayed as 0.05 Volts. That could be the peak voltage or some sort of average voltage depending on the meter. Either way you can't calculate the power without knowing what the load is. If the load was just the volt meter then it's likely the power was very very low because the resistance of a voltmeter is designed to be high. Connect a known load resistor and repeat the experiment.

If you really did mean "0.05 Watts" then you need to tell us how long it was at 0.05 Watts? If each pass generated 0.05W for half a second and you repeat that once per second (60 times per min) then the average power will be 0.05/2 = 0.025W. That's because half the time it's generating 0.05W and half the time nothing.
 
If you actually did the “experiment” let’s say you have a good permanent magnet of 2”*2” area and you moved it
with 1m/sec.
E.M.F.=Br*L*v [see: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/genwir2.html]
E.M.F.=1[Wb/m^2]*[2*2.54/100]*1=0.0508 V
60 RPM=60/60=1 sec/turn. If the length of the wire loop is only 2”[0.0508 m] then the velocity v=0.0508 m/sec, only.
You’ll need 1200 rpm in order to achieve 0.05 V.
 

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