Class notes
Inductance ,capacitance ,impedance
- Course
- Institution
Notes on inductance, inductive reactance ,capacitors ,capacitive reactance ,impedance ,time constants.
[Show more]
Seller
Follow
elizabethagostino
Content preview
Inductance● Inductance is the behavior of a coil of wire in resisting any change of current through the
coil
● Symbol is L
● Measured in henrys
● 1 henry of inductance generates 1 volt of induced voltage when current changes at 1
amp per second
● All conductors have inductance because they all generate back voltage
● Can be connected in the same way as resistors
● Coils are wound on a spool or bobbin,wire has very thin enamel insulation
● If different windings need insulation between them (like a transformer) an insulating
film/normex is used and core is added afterwards
● Inductors in series and parallel are calculated how resistors are for their respective
circuits
● If changing magnetic fields do not affect each other the total inductance is the sum of the
individual inductors
● If inductors are connected in parallel such that the changing magnetic field doest effect
each other, the total inductance is calculated like resistors in parallel (reciprocal)
Time constant of inductors
● Current doesn't rise instantly,it finds a minimum of opposition and then starts to flow
● The change in current from 0 to maximum induces a minimum EMF that opposes current
flow
● The time required for current to rise to 63% of its peak value is the TC of the circuit
● TC is determined by the value of inductance and resistance in the circuit
● Formula is L / R
● It takes 2 TC to rise to 86%
● It takes 3 TC to rise to 95%
● It takes 5 TC to rise to 100% (maximum)
● Back EMF kicks in when current decreases quick and the process is slowed because the
current is affected by the opposition of the back EMF
Capacitors
● Capacitance is the ability of a body to store electrical charge
● capacitors/condenser stores energy in the electrical field that exists between 2
conductors (plates) separated by a dielectric(insulator)
● Measured in farads
● Symbol is C
, ● 1 farad is the capacity required to hold 1 coulomb of electricity under 1v
● Mostly measured in micro or pico farads
● Formula is Q / E where Q is change in coulombs and E is voltage in volts
● 1 plate attached to positive side and one attached to negative side, electrons are drawn
from positive to negative
● There is no current flow across an insulator but the plates accumulate excess electrons
which results in plates being charged
● Current flow stops when capacitor becomes fully charged
● Used for timing,filtering and isolating AC or DC
● Capacitance is affected by 3 variables
● Area of plates,separation distance between plates and composition of the dielectric
● Large plate = more electrons can be stored ,small plate = less electrons can be stored
● Close = stronger , further = weaker
● More electrons stored on the negative plate
● If plates become too close the field cna become so strong that it passes through the
insulator and breaks down the dielectric causing a short circuit or damage (dielectric
breakdown)
● Due to this all capacitors are rated at least 10% higher than the highest approved
voltage in the circuit (DC rating)
● In an RC circuit current leads voltage by 90 degrees
● In an RL circuit voltage leads current by 90 degrees
● 2 ways capacitors store energy are electrostatic attraction across the dielectric and
distortion of electron orbits of atoms in the dielectric
● Dielectric stress is when electrons are attracted to the positive plate and protons are
attracted to the negative plate
● Electrolytic capacitors: polarized,only to be used in DC circuits,low working voltage,large
amounts of capacity
● Non electrolytic (paper): low value of capacitance needed,plates are made of paper with
metal foil and wax paper coiled, may be encapsulated in plastic,found in aircraft
magnetos
● Mica capacitor: small capacity required but high working voltage,stacks of foil
sandwiched between sheets of mica and encapsulated in plastic
● ceramic capacitors : high voltage, low capacitance,leads are attached to silver plating
and the entire unit is covered with protective insulation
● High voltage capacitor: high voltage application,paper capacitor in a metal container
filled with oil, oil flows when voltage surge breaks through the insulator and will restore it
by acting as the insulator,self healing
● Variable capacitor: changes its capacity
● TC is how long the capacitor takes to charge and discharge
● Capacitors in series use the inverse rule
● Capacitors in parallel just get added
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller elizabethagostino. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $9.79. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
67866 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now