Discharging graphs: everything decays exponentially

Capacitance & Charge/Discharge — AQA A-Level Physics

When discharging through a resistor (no powerThe rate of energy transfer. Measured in watts (W). supply):
Electrons flow back from the negative plate to the positive plate.
CurrentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A)., chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C)., and p.d. all decrease exponentially from their initial values to zero.
All three discharge graphs have the same exponential decay shape.
Higher resistanceThe opposition to currentThe rate of flow of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. Measured in amperes (A). flow. The ratio of potential difference to currentThe rate of flow of charge. Measured in amperes (A).. Measured in ohms (Ω).: slower discharge (current is smaller, charge drains more slowly).
Lower resistanceThe opposition to current flow. The ratio of potential difference to current. Measured in ohms (Ω).: faster discharge.

Reading discharge graphs

The area under a current-time graph equals the charge stored: $Q = I x t$.
The gradient of a charge-time graph gives the current at that instant: $I = DeltaQ/Deltat$.
To find the gradient of a curve: draw a tangent at that point and calculate its slope.

Examiner Tips and Tricks

Be comfortable sketching both charging and discharging graphs.
Remember: conventional currentThe direction of current flow defined as from positive to negative. Opposite to the direction of electron flow. flows opposite to electron flow.