Capacitance - 23 Flashcards
Define capacitance
Charge stored per unit of P.D
Charge stored on a capacitor is directly proportional to what?
The potential difference across it.
what does C represent
Capacitance
What is capacitance measured in ?
Farads (F)
When a capacitor is connected to a power supply what happens, in terms of the electrons?
Electrons move from the battery onto one of the plates which becomes negatively charged
What happens to the positive plate when the battery is plugged into the capacitor?
electrons move from he positive plate to the battery
What type of field is created between the two plates of a capacitor?
Electric field
If the capacitor is disconnected from the battery across a resistor what happens?
It discharges
What does A represent when referring to capacitance?
Area of overlap
What is epsilon 0?
permittivity of free space - 8.85x10-12
What does epsilon r reprisent?
relative permittivity of the dielectric places between the plates
What is a dielectric?
An insulator places between the plates of a capacitor
The charge of a capacitor increases with what?
potential difference - straight line from bottom left to top right
What does E represent?
Energy stored in the capacitor (J)
Energy stored is what on a Q/V graph?
area underneath
what graph is the same when charging and discharging a capacitor?
Current (I) against time
What two graphs flip when charging and discharging for a capacitor?
Charge and Voltage against time
Current is initially high when?
start of charging a capacitor/ start of discharging
What does the area under a Q/T graph represent?
Charge stored by the capacitor
time constant is equal to what percentage fall in charge?
37%
What are three uses of a capacitor?
smoothing unwanted voltage in a circuit, back up power supplies and timing circuits
What is the charge on opposite capacitor plates?
equal and opposite
What is used to charge a capacitor at a constant current/
a variable resistor
How do you measure the potential difference of a capacitor?
using a high resistance voltmeter connected in parallel
How do you test for how P.D changes with time for a capacitor?
use the variable resistor to keep the current constant and use a stopwatch and measure the voltmeter reading at constant intervals.
What can be used to measure the energy transfer from a charged capacitor to a bulb?
a joulemeter
