19.2 A2 Level

Energy stored in a capacitor

7 flashcards to master this topic

Key Concept Flip

How can the energy stored in a capacitor be determined from a potential-charge graph?

Answer Flip

The electric potential energy stored in a capacitor is equal to the area under the potential-charge (V-Q) graph. This area represents the work done to charge the capacitor.

Definition Flip

State the formula that relates the energy (W) stored in a capacitor to its charge (Q) and potential difference (V).

Answer Flip

The energy stored in a capacitor is given by the formula W = (1/2)QV, where W is the energy in Joules, Q is the charge in Coulombs, and V is the potential difference in Volts.

Definition Flip

State the formula that relates the energy (W) stored in a capacitor to its capacitance (C) and potential difference (V).

Answer Flip

The energy stored in a capacitor can also be calculated using the formula W = (1/2)CV², where W is the energy in Joules, C is the capacitance in Farads, and V is the potential difference in Volts.

Calculation Flip

A 100μF capacitor is charged to a potential difference of 10V. Calculate the energy stored in the capacitor.

Answer Flip

Using the formula W = (1/2)CV², W = (1/2) * (100 × 10⁻⁶ F) * (10 V)² = 0.005 J. The energy stored in the capacitor is 0.005 Joules.

Calculation Flip

A capacitor stores 0.02 J of energy when charged to 200V. Calculate the charge on the capacitor.

Answer Flip

Using the formula W = (1/2)QV, rearrange to find Q = 2W/V. Therefore, Q = (2 * 0.02 J) / 200 V = 2 × 10⁻⁴ C. The charge on the capacitor is 0.2 mC.

Key Concept Flip

How does increasing the potential difference across a capacitor affect the energy stored?

Answer Flip

Increasing the potential difference across a capacitor increases the energy stored. Since energy is proportional to V² (W = 1/2 CV²), doubling the voltage quadruples the energy stored.

Key Concept Flip

A parallel-plate capacitor is fully charged and then disconnected from the power supply. If the plate separation is doubled, how does the stored energy change?

Answer Flip

Doubling the plate separation halves the capacitance (C=ε₀A/d). Since the charge remains constant (isolated system), energy increases (W=Q²/2C). Halving C, doubles W, resulting in double the energy.

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19.1 Capacitors and capacitance 19.3 Discharging a capacitor