Capacitors Flashcards
What is a capacitor?
A device that stores charge
Define capacitance
the charge stored per unit pd
Name 3 uses of capacitors
smoothing circuits, timing circuits, pulse producing circuits
Why is only half the energy stored in the capacitor (1/2 QV) ?
energy is dissipated in the wires due to resistance in the circuit
Draw current/time , pd/time and charge/time graphs for capacitor discharge
current time- exponential decrease
pd time- exponential decrease
charge time- exponential decrease
Draw current/time , pd/time and charge/time graphs for capacitor charging
current time- exponential decrease
pd time- exponential increase (inverse of exponential decrease)
charge time- exponential increase (inverse of exponential decrease)
What is the time constant?
RC
At time, RC after discharge the charge falls to what?
0.37 (37%) of its initial value
At time, RC after charging the charge is
63% of the final value
The time constant is?
the time taken for the charge to reach 63% of its final value
What is a dielectric?
an electrically insulating material that increases the ability of a capacitor to store charge.
Give examples of a dielectric
polythene, waxed paper
Why does a dielectric increase capacitance?
the positive side of the dielectric attracts more electrons from the battery onto the negative plate
the negative side of the dielectric pushes electrons back to the battery from positive plate
How can a large capacitance be achieved?
making the area of overlapping plates as large as possible. making the plate spacing as small as possible. filling the space between the plates with a dielectric.
