Summary
Summary OCR-A A2 Level Capacitance Notes
- Course
- Institution
- Book
A summary of the OCR Physics A textbook for capacitance
[Show more]
Connected book
Book Title:
Author(s):
- Edition:
- ISBN:
- Edition:
More summaries for
-
A Level Physics OCR A - Particles and Medical Physics
-
A Level Physics OCR A - Newtonian World and Astrophysics
-
A Level Physics OCR A - Electrons, Waves and Photons
Seller
Follow
annawoodbridge
Content preview
CapacitanceCapacitors
● Electrical components in which charge is separated
● A capacitor consists of 2 metallic planets separated from each other by an
insulator
○ Known as a dielectric such as air, paper, ceramic or mica
● A capacitor connected to a cell of e.m.f. 𝜺
○ When the capacitor is connected to the cell,
electrons flow from the cell for a short time
○ They can’t travel between the plates because of the
insulation
○ The brief current means electrons are removed
from plate A of the capacitor and at the same time,
electrons are deposited into the other plate B
○ Plate A becomes deficient in electrons so it acquires
a net positive charge
○ Plate B gains electrons and acquires a net negative
charge
○ The current in the circuit must be the same at all points and charge must
be conserved, so the 2 plates have an equal but opposite charge of
magnitude Q
○ Therefore, there is a potential difference across the plates
○ The current in the circuit falls to 0 when the p.d. across the plates is equal
to the 𝜺 of the cell
○ The capacitor is then fully charged
○ The net charge on the capacitor plates is 0
● The capacitor is therefore a device that separates electrical charge into -Q and +Q
● Capacitance indicates the amount of charge Q that the capacitor can store for a
given p.d. V
● The capacitance of a capacitor is defined as the charge stored per unit p.d. across
it
𝑄
○ C (farads F) = 𝑉 or Q = VC
● For any capacitor, the greater the amount of positive and negative charge stored
on the 2 plates, the greater the p.d. across them
○ So the charge on the capacitor is always proportional to the p.d.
○ 1 F = 1 Coulomb per Volt
● Supercapacitors are specialist capacitors with high values of capacitance (1000s
of farads)
, ○ Unlike rechargeable batteries that
degrade over time, supercapacitors can
be charged over and over again
● For 2 or more capacitors in parallel:
○ The p.d. across each capacitor is the
same
○ Electrical charge is conserved, therefore
the total charge stored is equal to the
sum of the individual charges stored by
the capacitors
■ Q = Q1 + Q2 + … + Qn
○ The total capacitance is the sum of the individual capacitances of the
capacitors
■ C = C1 + C2 + … + Cn
● All the capacitors in series store the same
charge
● This is true when they have different
capacitors
● The cell is connected to the left hand plate of
the capacitor of capacitance C1 and to the
right hand plate of the capacitor of
capacitance C2
○ These plates acquire equal and
opposite charges as electrons flow to and from these plates
○ The middle 2 plates are not connected to the cell because of the presence
of the dielectric layers, but transfer of electrons between these plates
ensures that they also acquire charge Q of the same magnitude
○ The overall charge of each capacitor is 0 but the magnitude of the charge
on each plate is Q
● For 2 or more capacitors in series:
○ According to Kirchoff’s 2nd law, the total p.d. across the combination os the
sum of the individual p.d.s across the capacitors
■ V = V1 + V2 + … + Vn
○ The charge Q stored by each capacitor is the same
○ The total capacitance C is given by the equation
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 annawoodbridge. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $5.82. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
56326 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now