Capacitors (Module 23) Flashcards
What is a capacitor made from?
Two parallel metal plates opposite each other.
What happens when these plates are connected to a battery?
Electrons move through the battery and are forced from its negative terminal of the battery onto one of the plates. An equal number of electrons leave the other plate to return to the battery via its positive terminal. So each plate gains an equal and opposite charge.
Define capacitance
The capacitance of a capacitor is defined as the charge stored per unit pd.
What is the unit of capacitance?
OOOOF, I mean F (Farad)
Why does a capacitor store energy?
Because electrons are forced onto one of its plates and taken off the other plate.
What is the energy in a capacitor stored as?
Electric potential energy
What is the equation for energy stored by the capacitor?
e = 1/2QV
Give an example of a use of a capacitor.
- Timing circuits and alarms
- Backup power supplies
- Smoothing circuits
- Tuning circuits
- Filter circuits
- Pulse producing circuits
What is the energy stored in a thundercloud equal to?
e = 1/2QEd (Where E is the electric field strength and d is the height of the thundercloud)
Since the electric field strength on a thundercloud doesn’t change, how would you find the new value of energy stored at its new height?
The differences between the original height and the new height. ( Delta d = d1 -d)
What is the relationship between the discharge of a capacitor and time?
Exponential
The quantity RC is called the ____ ________ for the circuit. Fill in the gaps.
Time Constant
What is the time constant?
This is the time taken for a quantity to decrease exponentially to 0.37 ( 1/e) of its initial value.
What is a dielectric?
A dielectric is an insulating material that increases the ability of a parallel plate capacitor to store charge.
What materials are dielectrics usually made from?
Polythene and Waxed Paper.
