Capacitance
Capacitors - OCR A-Level Physics
Key Definition
Capacitance
The charge stored per unit potential difference across the capacitor. Measured in farads (F).
The charge stored per unit potential difference across the capacitor. Measured in farads (F).
$$C = \frac{Q}{V}$$
- 1 $farad = 1 coulombThe SI unit of chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. One coulomb is the chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). transferred by a current of 1 A in 1 second. per voltThe SI unit of potential difference and EMFElectromotive force. The energy transferred per unit charge by a source in driving charge around a complete circuit. Measured in volts (V).. One volt is one joule per coulomb.. This$ is an enormous capacitanceThe chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). stored per unit potential difference across a capacitor. Measured in farads (F).; real capacitors are typically measured in microfaradsA unit of capacitance equal to 10⁻⁶ farads (μF), commonly used for practical capacitors. or picofaradsA unit of capacitance equal to 10⁻¹² farads (pF), used for very small capacitors..
- A capacitor stores energyThe capacity to do work. Measured in joules (J). in the electric fieldA region of space where a charged particle experiences a force. Field strength E = F/Q. between its plates, not by storing free electronsElectrons not bound to any particular atom, free to move through a conductor. Also called delocalised or conduction electrons..
- The total charge on a capacitor is always zero: +Q on one plate and -Q on the other. When we say 'charge stored Q', we mean the magnitude on one plate.
Common Mistake
MEDIUM
Wrong: A capacitor stores charge.
Right: A capacitor stores energyThe capacity to do work. Measured in joules (J).. It separates charge (+Q on one plate, -Q on the other) but the net charge is zero.
Right: A capacitor stores energyThe capacity to do work. Measured in joules (J).. It separates charge (+Q on one plate, -Q on the other) but the net charge is zero.