RC Circuit Charging & Discharging – AP Physics 2 | ShowMeClass

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RC Circuit Charging & Discharging

AP Physics 2 · Unit 4: DC Circuits

Learning Objectives

Describe exponential charging/discharging of a capacitor

Calculate the time constant τ = RC

Analyze V_C(t), I(t), and Q(t) curves

Explain why I is maximum at t = 0 during charging

Charging Equations

Discharging Equations

Time Constant

τ = RC is the time to reach ~63% of final value during charging.

At 1τ: 63.2%
At 2τ: 86.5%
At 3τ: 95.0%
At 5τ: 99.3% (≈ fully charged)

Graph Colors

V_C (capacitor voltage)

I (current)

Q (charge on capacitor)

τ markers

RC CircuitCapacitorTime ConstantAP Physics 2

τ = RC =—

t =—

V_C =—

I =—

Q =—

V_C(t)

I(t)

Q(t)

All

Mode

EMF ε (V) 12

Resistance R (kΩ) 10

Capacitance C (μF) 100

Speed 1×

Instantaneous Values

📝 Quick Quiz▼

1. The time constant τ of an RC circuit equals:

R / C R × C R + C C / R

2. During charging, the current is maximum at:

t = τ t = 5τ t = 0 t = ∞

3. After 1 time constant, a charging capacitor reaches approximately:

50% of ε 63% of ε 37% of ε 100% of ε