Module 6 - 6.1.2 Energy

Question 1

The energy stored by a capacitor must equal

Answer 1

the work done to separate the charges on the two plates

Question 2

Charge is proportional to

Answer 2

Pd, where constant of proportionality = capacitance

Question 3

Charge - Pd Graph (2)

Answer 3

• gradient = capacitance
• area underneath = energy stored in capacitor

Question 4

Capacitors discharge

Answer 4

slowly due to charge leakage, so the stored energy decreases

Question 5

Uses of Capacitors

Answer 5

Flash devices for cameras
- charge is stored in capacitor and released quickly
- resulting high current excites a gas resulting in the energy being converted to a bright flash of light

Back up energy supplies
- large capacitors are used in back up power supplies in data centres to provide emergency current for a very short time
- long enough to shut down equipment and save data if mains power fails