AQA Exam -- oscilloscope question concept

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Homework Help Overview

The discussion revolves around the behavior of voltages in a circuit involving a resistor and a capacitor, particularly in the context of AC generation and oscilloscope readings. Participants are exploring how the voltage readings differ between the resistor and capacitor during charging and discharging phases.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the nature of voltage readings across circuit components, particularly why the resistor shows negative voltage while the capacitor remains positive. There are inquiries about the direction of current flow during the discharge of the capacitor through the resistor and how this relates to the oscilloscope's measurements.

Discussion Status

The discussion is active with participants raising questions about the interpretation of voltage direction and the relationship between the current through the resistor and capacitor. Some guidance has been offered regarding the oscilloscope's reference point and how it affects voltage readings, but there is no explicit consensus on the interpretations being explored.

Contextual Notes

There is mention of specific figures and questions from an exam context, indicating potential confusion about the application of circuit diagrams and waveform types in the problem set. Participants are navigating through these constraints while discussing the concepts.

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Homework Statement
aqa paper question images below
https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2017/june/AQA-74083A-QP-JUN17.PDF
3.2 question
Relevant Equations
no relevant equation i think
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can anyone explain why the voltage reading is negative for the resistor over a time period , yet the capacitor reading always stays positive ?
In AC generation the voltages goes from negative to positive, how exactly does this affect the circuit components voltages? I am not sure how AC affects the components of the circuit When charging and discharging? i understand that the capacitor is charging and discharging and the general shape of the curve.
thank you in advance
 
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Think about which way the current is flowing as the charged capacitor now discharges through the resistor (during the time when generator is at zero volts)
 
scottdave said:
Think about which way the current is flowing as the charged capacitor now discharges through the resistor (during the time when generator is at zero volts)
upwards? Is the voltage direction of the resistor always opposite to the capacitor?
essentially does the resistor current flow in the opposite direction to the capacitors?
 
Please don't think of voltage as having a "direction". Given a certain reference point, another point may have higher or lower voltage than the reference. This would read as a positive or negative voltage. You need to note that the oscilloscope has moved it's reference point. The voltage at the "top" of the resistor is equal to the output voltage of the signal generator in this circuit (when the switch is closed). So think about how the oscope is measuring across the resistor.
 
Are you sure the circuit in Figure 9 (question 02.3) applies to question 02.6? It says the waveform is shown in Figure 10 (not Figure 12). Question 02.6 is not about AC (a sinusoidal waveform), it is a voltage alternating between a constant positive value and zero.
 

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