Finding frequency of an AC current sin wave?

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Homework Help Overview

The problem involves determining the frequency of an alternating current (AC) represented by the equation I = 475 sin(9.43t), where I is in milliamperes and t is in milliseconds. The focus is on understanding the relationship between angular frequency and frequency in Hertz.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the conversion of units and the implications of the time variable being in milliseconds. There are attempts to relate the angular frequency to Hertz, with some questioning the significance of the current's units.

Discussion Status

The discussion is active, with participants exploring different interpretations of the problem. Some have provided insights regarding the units of time and their effect on the frequency calculation, while others have expressed confusion about the initial approach.

Contextual Notes

There is an emphasis on the importance of the time unit being in milliseconds, which affects the calculation of frequency. Participants are also navigating the distinction between angular frequency and standard frequency in Hertz.

jlmccart03
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Homework Statement


An AC current is given by I= 475 sin( 9.43 t), with I in milliamperes and t in milliseconds. Find the frequency.

Homework Equations


w = 2pi*f

The Attempt at a Solution


I got 9.43/2pi which is 1.5 Hz, but that is wrong. I honestly have no idea what to do to find the Hz.
 
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Pay close attention to the units specified :wink:
 
gneill said:
Pay close attention to the units specified :wink:
Would I convert milliamperes to amperes and get 0.001501 instead of 1.5? Also the only units are millamperes and frequency is in Hertz which is cycles per second.
 
The current units are inconsequential. They don't affect frequency. However:

jlmccart03 said:
... and t in milliseconds.

is important.
 
gneill said:
The current units are inconsequential. They don't affect frequency. However:
is important.
The 9.23t is in milliseconds correct? Hertz is in seconds though so instead of 9.23 it would be 0.00923 s correct? So I would get 0.00923/2pi = 0.001501 Hz.
 
jlmccart03 said:
The 9.23t is in milliseconds correct? Hertz is in seconds though so instead of 9.23 it would be 0.00923 s correct? So I would get 0.00923/2pi = 0.001501 Hz.
No, you've gone the wrong way with the scaling.

Think of it this way: If t is in milliseconds, then after 1 millisecond the argument of the sine function should give 9.43 radians. That is, the constant 9.43 is associated with the units: radians/millisecond.
 
gneill said:
No, you've gone the wrong way with the scaling.

Think of it this way: If t is in milliseconds, then after 1 millisecond the argument of the sine function should give 9.43 radians. That is, the constant 9.43 is associated with the units: radians/millisecond.
OHHHHHH so instead it is 9430 rad/s. Ok so the answer should be 1500 Hz. Thanks!
 
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