Finding frequency of an AC current sin wave?

[jlmccart03]

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.

 

[gneill]

Pay close attention to the units specified

 

[jlmccart03]

Pay close attention to the units specified

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.

 

[gneill]

The current units are inconsequential. They don't affect frequency. However:

... and t in milliseconds.

is important.

 

[jlmccart03]

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.

 

[gneill]

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.

 

[jlmccart03]

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!