3.7.4 - Capacitance Flashcards
What is the relationship between capacitance, area, and separation of the two plates?
the capacitance is proportional to the area of the plates and inversely proportional to the separation of the two plates.
How do you produce a compact component with a high capacitance?
separate the two plates with an insulating material and rolls it up; this allows a large surface to be enclosed in a small volume.
What does introducing a material between the conducting surfaces do?
it changes the capacitance and also, since there is no air gap, the permittivity changes
What happens when the two plates are connected to a battery?
electrons are removed from one plate and moved around the circuit to the other plate. This leaves the first plate with a positive charge and travels to the other with a negative charge.
How are voltage and charge related in this circuit?
proportional
What is the symbol for a capacitor?
two equal length lines perpendicular to the wire
what happens if the area of the plates in increased?
more charge can be stored for the same applied voltage
What is capacitance measured in?
Farads, F
What can be an analogy for a capacitor?
water leaving a tank; the initial flow rate is high because of the pressure. As the level falls, so does the pressure, reducing the flow.
What is analogous to voltage
the pressure of water. As the membrane becomes more and more stretched, the pressure builds up
How do you calculate the total capacitance for multiple capacitors in series?
1/Ct = 1/C1 + 1/C2 + 1/C3 +….
How do you calculate the total capacitance for multiple capacitors in parallel?
Ct= C1 + C2 + C3 +….
What is one way to explore the behaviour of a capacitor? explain circuit set-up and method
Have a capacitor in series with a switch, cell, variable resistor, and ammeter, with a voltmeter connected over the capacitor in parallel. Take voltage readings at different times as the capacitor charges up. Open the switch at certain times to take a reading.
How is a constant current maintained?
By adjusting the variable resistor
How do you charge/ discharge a capacitor?
Connect it to a battery which allows electrons to flow from the battery’s positive terminal to one of the plates. They will collect here and create a negative charge. This charge will repel electrons away from the neighbouring plate, giving it a positive charge. This provides a potential difference. Disconnect the battery from the circuit and allow to charge left on the capacitor to be discharged at will.
When is a capacitor fully charged?
when the potential difference is the same as the PD of the battery
What is the area under a voltage-charge graph equal to?
the energy stored in a capacitor
How do you accurately measure the rate of discharge?
discharge it through a resistor since this will slow down the decrease in current and lose charge much slower so you are able to take accurate measurements
What do the discharge graphs look like for I/V/Q-ti
exponential decay
Explain the location of excess electrons when a (initially uncharged) solid conducting sphere has electrons transferred to it
They are on the outer surface of the sphere and are equally spaced since the electrons mutually repel
