Electricity: 3 - Capacitators Flashcards
What does a typical capacitor consist of?
Two conducting layers separated by an insulator like air.
What is the circuit symbol for a capacitor?
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What does a larger capacitance mean for a capacitor?
The larger the capacitance the more energy it can store and the longer it takes to charge.
What is the symbol for capacitance?
C
What are the units for capacitance?
Farads, F.
What will a capacitor of 1 farad store?
A capacitor of 1 farad will store 1 coulomb of charge when the potential difference across it is 1 volt.
What is a device that is to store charge called?
A capacitor.
What is capacitance known as?
The ability of a component to store charge.
What are the prefixes normally associated with farads and why is this?
Micro farads (μF)= 1x10-6 and nano farads (nF)= 1x10-9 as the farad is too large a unit for practical purposes.
What is the equation for capacitance using charge?
C=Q/V
In a resistive circuit what is the current and how is this shown on a graph?
In a resistive circuit the current is independent of a.c. frequency. On a graph of frequency against current the current is just a straight line.
In a capacitive circuit what is the circuit and how is this shown on the graph?
For a capacitive circuit, current increases as frequency increases. On a graph looks like a diagonal line across the graph which does not touch the axes.
What does a voltage charging capacitor graph against time look like?
A curved/hump line that curves outwards and goes through the origin.
What does a voltage discharging capacitor graph against time look like?
A line that curves down inwards and reaches the voltage of 0 and looks like a mountain drop.
What does a current charging capacitor graph against time look like?
A line that curves down wards like that of the voltage discharging and starts high with a high current the goes low but does not touch the axis.
What does a current discharging capacitor graph against time look like?
A line that curves upwards like a hump and similar to the voltage charging. Starts at minus and increases nearer to 0 but does not touch any of the axis.
What is the total energy stored in a capacitor equal to?
The area under the graph of charge against potential difference.
What is the equation to calculate the energy stored in a capacitor using the area under a charge against potential difference graph?
E=1/2 QV
What is the equation for the energy stored in a capacitor using capacitance and voltage and how is this formed?
E=1/2 QV
E=1/2 (CV)V
E=1/2 CV²
What is the equation for the energy stored in a capacitor using capacitance and charge and how is this formed?
E= 1/2 QV E= 1/2 Q(Q/C) E= 1Q ²/2C
What can be done to increase the time that it takes to charge a capacitor?
Increase the resistance in the circuit or increase the capacitance of the resistor.
What are uses of capacitors?
Blocking capacitor like in an oscilloscope, camera flash, touch screen phones and smoothing.
How does the capacitor work in a camera flash?
A camera flash requires a rapid release of energy. A battery can be used to charge a capacitor, the capacitor can then provide a very high current which produces a bright flash.
