Download Batteries and EMF

Capacitors and
batteries
Firdiana Sanjaya(4201414050)
Ana Alina(4201414095)
Definition of Capacitance

The capacitance C of a capacitor is defined as
the ratio of the magnitude of the charge on
either conductor to the magnitude of the
potential difference between the conductors:

Capacitance has SI units of coulombs per volt.
The SI unit of capacitance is the farad (F),
which was named in honor of Michael Faraday
Capacitors: devices for
storing charge
Parallel-Plate Capacitors

The charge stored in a
capacitor is proportional
to the potential
difference between the
two plates. For a
capacitor with charge Q
on the positive plate and
-Q on the negative plate,
the charge is
proportional to the
potential:

Q=CV
Parallel-Plate Capacitors

Type equation here.
The Spherical Capacitor
Capacitors with Dielectrics

A dielectric is a nonconducting
material, such as rubber, glass,
or waxed paper. When a
dielectric is inserted between
the plates of a capacitor, the
capacitance increases. If the
dielectric completely fills the
space between the plates, the
capacitance increases by a
dimensionless factor k, which is
called the dielectric constant of
the material.
Combinations of Capacitors
Series Combination

𝑄𝑆 = 𝑄1 = 𝑄2 = 𝑄3 =…

𝑉𝑆 = 𝑉1 + 𝑉2 + 𝑉3 +…

1
𝐶𝑠
1
1
1
1
2
3
= 𝐶 + 𝐶 + 𝐶 +…
Combinations of Capacitors
Parallel Combination

𝑄𝑝 = 𝑄1 + 𝑄2 + 𝑄3 +…

𝑉𝑝 = 𝑉1 = 𝑉2 = 𝑉3 =…

𝐶𝑝 = 𝐶1 + 𝐶2 + 𝐶3 +…
Energy stored in a capacitor

When a capacitor is being charge,positive
charge is transferred from the negatively
charged conductor to the positively charged
condustor.Work must therefore be done to
charge a capacitor.
Energy stored in a capacitor
𝑉=
𝑄
𝐶
𝑄 = 𝐶𝑉
Batteries and EMF

Batteries are capacitors that very good at
storing charge for short time periods, and they
can be charged and recharged very quickly.

A battery consists of two electrodes, the
anode (negative) and cathode (positive.
Usually these are two dissimilar metals such
as copper and zinc. These are immersed in a
solution (sometimes an acid solution). A
chemical reaction results in a potential
difference between the two terminals.

The voltage of a battery is also known
as the emf, the electromotive force.

Emf can be thought of as the pressure
that causes charges to flow through a
circuit the battery is part of.

A flow of charge is known as a
current.

Batteries put out direct current.
Current and Drift velocity

Current (I) is measured in amperes (A), and
is the amount of charge flowing per
second. I = q / t

The flow of positive charge in one
direction is equivalent to the flow of
negative charge in the opposite direction.

The direction of the drift velocity is
opposite to the electric field.

In a typical case, the drift velocity of
electrons is about 1 mm / s. The electric
field, on the other hand, propagates much
faster than this, more like 108 m / s.
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