A capacitor is a device that stores electrical charge and energy. It consists of two conducting plates separated by an insulating material called a dielectric. When a voltage is applied across the plates, electric charges of equal magnitude but opposite polarity build up on each plate. This creates an electric field within the capacitor. The amount of charge stored for a given voltage is proportional to the capacitance, measured in Farads, which depends on the size, shape and separation of the plates as well as the dielectric material. Capacitors are used widely in electronic circuits to store charge and energy, such as in camera flashes. The basic formula relating capacitance C, charge Q, and voltage V is Q = CV.

1. PHYSICS
CAPACITORS
Teacher: Telman Askeraliyev, MSc, Italy

2. INTRODUCTION
We noted earlier that an electric current represents a flow of charge
A capacitor can store electric charge and can therefore store
electrical energy
Capacitors are often used in association with alternating currents
and voltages
They are a key component in almost all electronic circuits

3. FIELDS
A capacitor is similar to a battery in that both store
electrical energy. But a capacitor can't actually produce
new electrons; it only stores them.
Like a battery, a capacitor has two terminals – positive
and negative. Inside the capacitor, the terminals connect
to two metal plates separated by a dielectric (an
insulating substance such as ceramic or glass that is
highly resistant to electric current) that keeps the plates
from touching each other and allows them to hold
opposite charges, maintaining an electric field.

4. DEFINITION
A capacitor is an electrical device which stores
charge. There are many types of capacitors: parallel plate
capacitors, cylindrical capacitors, tubular capacitors,
etc. Anything that stores charge is a capacitor.
Capacitors consist of two conducting surfaces
separated by an insulating layer called a
dielectric

5. YOU ARE A CAPACITOR!
You are a capacitor! (If you weren't, you wouldn't be able
to scuff your feet on carpet and zap your friends!) You
have a capacitance of about 100 pF (100 x 10 ^ -12 F).

6. APPLICATION
flash device for a camera (stores charge and energy)

7. CAPACITOR
A capacitor is device formed with two or more separated
conductors that store charge and electric energy.

8. CAPACITANCE
The electric field is proportional to the charges ±Q. If we double
the charges ±Q, the electric field doubles. Then the voltage
difference is Va-Vb proportional to the charge. This
proportionality constant depends on size, shape and separation of
the conductors.
If we call this constant, Capacitance, C, and the voltage
difference, V= V a-V b, then,

9. CAPACITANCE
• Capacitance, depends on the geometry of the two
conductors (size, shape, separation) and capacitance
is always a positive quantity by its definition (voltage
difference and charge of + conductor)
[N.B. C does not depend on voltage or charge]

10. UNITS
For all capacitors, there is a value which describes how
much charge can be put on a capacitor,
called capacitance.
Capacitance is measured in Farads (F = C / V)
• UNITs of capacitance, Coulomb/Volts or
Farads, after Michael Faraday
Capacitance is the amount of charge (Q) stored in a
capacitor per unit voltage (V).

11. CAPACITANCE

12. A SIMPLE CAPACITOR CIRCUIT
when switch is closed
electrons flow from
top plate into battery
and from battery
onto bottom plate
charge produces an
electric field across
the capacitor and a
voltage across it

13. BASIC FORMULA
For a given capacitor the stored charge q is
directly proportional to the voltage across it V
The constant of proportionality is the
capacitance C and thus
If the charge is measured in coulombs and the
voltage in volts, then the capacitance is in
farads
V
Q
C 

14. QUIZ 1
A 10 F capacitor has 10 V across it. What
quantity of charge is stored in it?

15. QUIZ 2
A 10-nanofarad parallel-plate capacitor holds a charge of
magnitude 50 C on each plate.
What is the potential difference between the plates?

16. LESSON TAKEAWAYS!

17. THANK YOU!