7.6 - Capacitance Flashcards
What are capacitors?
Electrical devices used to store energy in electronic circuits.
What are capacitors commonly used as?
A backup release of energy if the power fails in an electronic circuit (since as they store energy).
What are capacitors made of? (what do they look like internally)
Made of 2 conductive parallel plates with often a dielectric in between them, connected to a voltage supply.
These are often rolled up to reduce the overall size of the device.
What is a dielectric?
A substance that is a poor conductor of electricity, but are good insulators and can store electric energy in an electric field.
Why are dielectrics used in the formation of capacitors?
To ensure charge does not freely flow between the plates. They also enhance the performance of a capacitor by increasing its capacitance.
What is the capacitor circuit symbol?
⎯⎯⎯⎯⏐ ⏐ ⎯⎯⎯⎯
What is the definition of capacitance?
The charge stored per unit potential difference between the plates. (basically the capacity of energy stored in a capacitor).
What is the equation for capacitance?
C = Q/V
C = capacitance (F)
Q = charge (C)
V = potential difference (V)
What is the definition of potential difference?
The energy transferred per unit of charge flowing from one point to another V = E/Q
What is capacitance measured in?
Farads (F)
If a capacitor is made of parallel plates (as usual) what is Q and V in this context?
Q - the charge stored on the plates
V - the potential difference of the capacitor
What are polar molecules and where are found in a capacitor?
Polar molecules are molecules that have a positive and negative end (poles). These are found in the dielectric of a capactitor.
In what direction are the polar molecules aligned when there is no charge stored in the capacitor?
The polar molecules are pointing in a bunch of random directions since there is no electric field (due to no charge).
When charged is applied to a capacitor, what happens inside a capacitor, specifically the polar molecules in the dielectric?
The parallel plates becomes charged (one + one - ).
A uniform electric field is generated between the plates.
The polar molecules align (+ end of molecule faces - plate)
The molecules oppose the electric field applied by the capacitor
When the polar molecules align in the dielectric of a capacitor, what happens to the properties of the capacitor?
The polar molecules aligning reduces the overall electric field (created by the capacitor), which reduces the potential difference needed to charge the capacitor- SO the capacitance increases.
