Week 4 Flashcards
(26 cards)
Define Capacitors
devices that store electric charge and are used in electric
circuits
Capacitor: General Concept [list three]
- Two conductors of any shape, usually placed
close together - Arranged so that, at equilibrium, one has net
positive charge +Q and the other has net
charge –Q - This is a “device” that stores charge (actually,
separated + and - charges)
To “charge” a metal plate capacitor, attach it to a battery
or “power supply”, via wires which imposes a ____
V and causes electrons to move off the (+)
conductor and onto the (–) conductor
To “discharge” a capacitor (bring Q→0), the battery is
removed and a wire attached so _____
electrons can flow from the (-) conductor through the wire to the (+) conductor.
define capacitance
the amount of charge Q it can store per unit of potential difference V between the conductors
What is the formula of capacitance
𝐶 =|Q/deltaV|
C depends on the ______
physical construction of the capacitor (size, shapes, materials)
A “parallel plate capacitor”, consists of
two flat conducting plates, each area A, with a small separation d between them
Formula to calculate Parallel plate capacitor
𝐶 = |𝑄/V|=|𝑄/4pikd Q/A|=𝐴/4pikd
f an insulating material (“dielectric material”,
examples: water, oil, plastic, ceramic) is placed
between the two conductors, this will ______ C
increase
Calculate the total work to go from q=0 to Q by integrating:
U = Q^2/2C or U=1/2C(V)^2
if C=constant,
U increases as Q increases or as V increases
Two capacitors in parallel
terminals of both capacitors are connected together (by
a wire) and the + terminals of both are connected together
Parallel capacitors equation
Ceq = C1+ C2
Two capacitors in series
two capacitors are placed in “series” it means that there is
a wire connecting the + terminal of one to the – terminal of the other
Series combination equation
1/Ceq = 1/C1+ 1/C2
Define Electric current
to be rate at which a net amount of charge moves through a surface in a specified direction
By definition, “direction of current” is the direction ____
that + charges would move. If – charges are moving, this is “current” also but the “direction of current” is opposite to the direction the - charges move
The average current during time deltat formula
Iavg =+_ (DeltaQ/deltat)
If I>0 this means ______
+ charges are moving right or - charges are moving left
If I<0 this means_____
+ charges are moving left or - charges are moving right
A negative current in one direction (e.g. +x) is equivalent to a positive current in the ____ direction (-x)
opposite
Conductors having different sizes and shapes and/or made from different materials have different numbers of mobile charges inside and the charges experience different interactions with atoms inside the materials, so current flows ____
more or less easily through some conductors than others
Resistance formula
R = |V/I|
