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The Time Constant RC

Given dQ/dt = -Q/RC, we get exponential equations for charge, current and time.
  • For charge Q = Q0e-t/RC.
  • For potential difference V = V0e-t/RC.
  • For current I = I0e-t/RC.
The constant of proportionality is the time constant RC where R is the resistance of the fixed resistor and C is the capacitance of the capacitor. The unit of RC is the second and it is the time taken for the capacitor to discharge to 1/e (37%) of its original charge.

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Specification: AQA Physics (7408), A-level, 3.7.4.4 Capacitor charge and discharge. Topic: Capacitors.

Key terms in this lesson

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The product of the magnetic flux density and the area through which the field passes at right angles to it, measured in weber.

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