What is the voltage? AC circuit

AI Thread Summary
The discussion centers on calculating the voltage across a resistor in an AC circuit with a 60 Hz power source and a peak voltage of 12.0 V. The current voltage at a specific moment is 10.0 V and decreasing, prompting a query about the voltage 1.5 ms later. The initial calculation attempted to use the cosine function but yielded an incorrect result. To find the correct voltage, one must first determine the time at which the 10.0 V occurs in the waveform before adding 1.5 ms. This approach clarifies that the original calculation did not align with the question's requirements.
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A 60 Hz power source with a peak voltage of 12.0 V is connected to a resistor. At a particular instant the voltage across the resistor is 10.0 V and decreasing. What is the voltage 1.5ms later.

I tried using the equation

v= V cos(2 pi ft)

v= 12.0V cos(2pi (60Hz)(1.5 X 10^-3s))
v= 10.13 volts.. but this is incorrect. Help please
 
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:rolleyes:Please help me out. Thank you.
 
If you are taking the instant of 12V to be your t=0, you have to first figure out at what time the 10V occurs in the waveform. Then add the 1.5 ms onto that number to find the voltage at 1.5 ms after the 10V. Does that make sense? What you have found is the voltage at 1.5 ms after your max voltage of 12V, which is not what the question is asking.
 

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