chapter 21 - capacitance Flashcards
Describe the construction of a capacitor.
Two conducting plates seperated by an insulator.
What is the relationship between charge stored and pd across a capacitor?
Charge is proportional to voltage
Describe what happens to the two plates of an uncharged capacitor when a p.d. is applied to it?
Electrons/charge flows off of one plate and flows on to the other causing one to become positive and the other negative.
What units are equivalent to a Farad?
CV-1 or coulombs per volt
How do you calculate the total capacitance for capacitors in parallel?
Ct = C1 + C2 + C3 + …. Cn
How do you calculate the total capacitance for capacitors in series?
1/CT = 1/C1 + 1/C2 + 1/C3….
If capacitors are connected in series what quantity is the same for all capacitors?
Charge stored
If capacitors are connected in parallel what quantity is the same for all capacitors?
p.d.
What is represented by the area under a p.d. - charge graphs?
Electrical energy transferred OR work done.
What is represented by the gradient of a charge-p.d. graph for a capacitor?
Capacitance
What is the relationship between energy stored and p.d. on a capcitor?
Energy stored is proportional to p.d. squared
What is the relationship between energy stored and charge on a capacitor?
Energy stored is proportional to charge squared
Out of Q, V and I which variable(s) follow the relationship x = x0 e-(t/RC) when discharging a capacitor?
Q, V and I
Out of Q, V and I which variable(s) follow the relationship x = x0 e-(t/RC) when charging a capacitor?
I
Out of Q, V and I which variable(s) follow the relationship x = x0 (1 - e-(t/RC) ) when charging a capacitor?
Q and V
How do you calculate time constant in a capcitor circuit?
Capacitance x resistance
What is meant by the constant-ratio nature of exponential decay?
In equal time intervals the quantity decreases by equal factors.
How much charge remains after one time constant when discharging a capacitor?
e-1 OR 0.37 OR 37%
How much charge remains after n time constants when discharging a capacitor?
Xo x e^-n
What is represented by the gradient of charge-time graph when charging a capacitor?
Charging current.
State a two uses of capacitors.
Energy storage e.g. for camera flashes, spot welding…, timing circuits, voltage smoothing, audio filters.
