Astronuc said:How else would one propose to measure the voltage across a RC cirucit as a function of time, especially for short time constants?
Using a CRO (oscilloscope) is pretty standard. Of course, the impedance of the CRO needs to be high enough so as not to effect the measurement.
The reason has to do with the grounds on your instruments, and I suspect you haven't read the entire instructions that accompany your lab. The voltage across the cap is found as the difference between that across both R-C, which you mention, and that across R, which is found on the other channel of the CRO. You can't measure Vc directly because your CRO and source both have grounds. Once you connect the source as shown, the CRO ground must go to the same place, that is, you cannot put gnd and probe across the cap anymore.dizi100 said:For ac voltage,voltage of the power supply equals voltage across both capacitor and resistor.
If i connect a CRO across both capacitor and resistor,i in fact measure the voltage of the power supply,right?
According to my lab manual,it states that i can mesure the voltage across the capacitor by connecting a CRO across the capacitor and resistor.
i really don't understand...
http://upload.u-state.com/images/1194185727.bmp
An RC circuit is a circuit that contains a resistor (R) and a capacitor (C) connected in series. The resistor limits the flow of current, while the capacitor stores and releases electrical charge. When a voltage is applied to the circuit, the capacitor charges and then discharges, creating a time-varying voltage.
A CRO is used to measure RC circuit voltage because it displays the changing voltage over time, allowing for the visualization of the time-varying voltage of the circuit. It also has a high input impedance, meaning it won't significantly affect the voltage being measured.
To measure voltage using a CRO, connect the probe to the input of the CRO and the ground clip to the ground of the circuit. Adjust the timebase and voltage settings on the CRO until the waveform is visible. The voltage can be read from the vertical scale on the CRO display.
Measuring RC circuit voltage allows for the analysis of the behavior of the circuit, such as the charging and discharging of the capacitor. It also helps in troubleshooting and determining if the circuit is functioning as expected.
The time constant of an RC circuit is calculated by multiplying the resistance (R) in ohms by the capacitance (C) in farads. The resulting value is in seconds and represents the time it takes for the capacitor to charge to 63.2% of the applied voltage or discharge to 36.8% of the original voltage.