6B.1 Capacitor Basics Flashcards
for a simple circuit to function we need
a full conducting path as electrons can’t escape their conductor and move across an empty space in the circuit
for a simple circuit to function we need
a full conducting path as electrons can’t escape their conductor and move across an empty space in the circuit
a capacitor is
an electrical circuit component that can be used to store charge and therefore can be used as energy store
how do we create a capacitor
having two metal plates with a gap between them, connecting one to a negative terminal and another one to the positive terminal, the metal plate connected to the negative terminals would collect the electrons from the power supply forming a negative supply, and the metal plate connected to the positive power supply would have the electrons from the metal going to the positive power supply forming a positive charge since both metal plates are now negatively and positively charged the attraction between them will cause an electric field, which will keep increasing until the potential difference across the gap = the potential difference of the power supply, forming a way to store energy
what is capacitance
the measure of the capability of a capacitor; the amount of charge per unit voltage across the capacitor, measured in farads
what is the equation for a capacitor
capacitor = charged stored / potential diffrence across the capacitor
what is a coulombmeter
a device that will measure the amount of charge directly
how can you use a coulometer to measure capacitance
by charging a capacitor using diffrent voltages and then always discharging through a coulombmeter, then plot a graph with V on the x-axis and Q on the y-axis should produce a straight passing through the origin with m = Capacitance
the energy stored in a capacitor is given by
E = 1/2VQ
why is the energy stored in a capacitor given by E= 1/2QV
the original equation of E=QV doesn’t represent storing charge in a capacitor, because the following equation assumes that the voltage and charge are constant, which isn’t true, as to charge a capacitor it will start from zero charges as it keeps increasing its voltage until it reaches the same potential difference of the power supply, every time we add a little extra charge which has to be done by increasing the voltage and pushing charge on, which requires some energy (work done)
by finding the area under the graph we find the sum of every extra energy that we do, giving us the equation of 1/2QV
what are the two other formulas for E using E=1/2QV and Q=CV
E= 1/2CV^2 and E= 1/2 Q^2/C
how can we confirm our equation E= 1/2CV^2
by having a bunch of bulbs in a circuit (all parallel) with the same resistance then discharging capacitor energy into the bulbs in the circuit and varying the voltage to keep it the same brightness. so if the capacitance is getting lower increasing the voltage will make the bulbs brighter, therefore (E= 1/2CV^2) is conformed
how can we keep the total resistance constant in a circuit with bulbs when adding a new branch
to keep the resistance the same when adding a new branch is by making it parallel with the same number of bulbs as the other and add one bulb to each branch
