<< Chapter < Page Chapter >> Page >

Physical properties of the capacitor and capacitance

The capacitance of a capacitor is proportional to the surface area of the conducting plate and inversely proportional to the distancebetween the plates. It also depends on the dielectric between the plates. We say that it is proportional to the permittivity of the dielectric . The dielectric is the non-conducting substance that separates the plates. As mentioned before, dielectrics can be air, paper, mica, perspexor glass.

The capacitance of a parallel-plate capacitor is given by:

C = ϵ 0 A d

where ϵ 0 is, in this case, the permittivity of air, A is the area of the plates and d is the distance between the plates.

What is the capacitance of a capacitor in which the dielectric is air, the area of the plates is 0 , 001 m 2 and the distance between the plates is 0 , 02 m ?

  1. We need to determine the capacitance of the capacitor.

  2. We can use the formula:

    C = ϵ 0 A d
  3. We are given the area of the plates, the distance between the plates and that the dielectric is air.

  4. C = ϵ 0 A d = ( 8 , 9 × 10 - 12 ) ( 0 , 001 ) 0 , 02 = 4 , 45 × 10 - 13 F
Got questions? Get instant answers now!

Electric field in a capacitor

The electric field strength between the plates of a capacitor can be calculated using the formula:

E = V d

where E is the electric field in J . C - 1 , V is the potential difference in volts ( V ) and d is the distance between the plates in metres ( m ).

What is the strength of the electric field in a capacitor which has a potential difference of 300 V between its parallel plates that are 0 , 02 m apart?

  1. We need to determine the electric field between the plates of the capacitor.

  2. We can use the formula:

    E = V d

  3. We are given the potential difference and the distance between the plates.

  4. E = V d = 300 0 , 02 = 1 , 50 × 10 4 J . C - 1
Got questions? Get instant answers now!

Capacitance and the parallel plate capacitor

  1. Determine the capacitance of a capacitor which stores 9 × 10 - 9 C when a potential difference of 12 V is applied to it.
  2. What charge will be stored on a 5 μ F capacitor if a potential difference of 6 V is maintained between its plates?
  3. What is the capacitance of a capacitor that uses air as its dielectric if it has an area of 0 , 004 m 2 and a distance of 0 , 03 m between its plates?
  4. What is the strength of the electric field between the plates of a charged capacitor if the plates are 2 mm apart and have a potential difference of 200 V across them?

run demo

A capacitor as a circuit device

A capacitor in a circuit

When a capacitor is connected in a DC circuit, current will flow until the capacitor is fully charged. After that, no furthercurrent will flow. If the charged capacitor is connected to another circuit with no source of emf in it, the capacitor will discharge through the circuit, creating a potential difference fora short time. This is useful, for example, in a camera flash.

Initially, the electrodes have no net charge. A voltage source is applied to charge a capacitor. The voltage source creates an electricfield, causing the electrons to move. The charges move around the circuit stopping at the left electrode. Here they are unable totravel across the dielectric, since electrons cannot travel through an insulator. The charge begins to accumulate, and anelectric field forms pointing from the left electrode to the right electrode. This is the opposite direction of the electric fieldcreated by the voltage source. When this electric field is equal to the electric field created by the voltage source, the electronsstop moving. The capacitor is then fully charged, with a positive charge on the left electrode and a negative charge on the rightelectrode.

Questions & Answers

what is the formula for calculating tension
Kagiso Reply
You can use simultaneous equations or T=mg+ma
sibahle
- Which formula can you use if you want to calculate acceleration?
Pretty
to calculate acceleration you use formula Vf -Vi divided by the time (t)
sholan
What is the formula of calculating tension
sibahle Reply
I don't think there's a formula u just have to use all information in that type of situation
Gwebzi
can a mixture of atoms make a molecule
Keamogetse Reply
define the term "resultant"
Austin Reply
the sum of all the forces acting on an object
Think
carring out an investigation of the relationship of acceleration and net force with mass kept constant
Ronald
how to calculate coefficient of kinetic force
Bhereza Reply
kinetic friction × Normal force
Murunwa
how to get a valency electron
Really Reply
how to calculate acceleration due to gravity
Mpho Reply
how to calculate inertia and it's definition
sibahle Reply
how to draw a box of tall the force that act on the box mass is 5 .00 and lies a ramp with 30°
Thando Reply
how to determine Gravitational acceleration
Raman Reply
what is a force
Edith Reply
A force is a pull or push action that affects the shape, motion and direction of an object
Chauke
the different types of friction forces
Bhereza
different types of frictional forces are static frictional force(the object is stationery)and kinetic frictional force(the object is moving)
Raymond
static
Dineo
what is a vector
Nosihle Reply
a vector is a physical quantity that have both magnitude and direction
Edith
how to calculate the magnitude and direction if, P=500N,10°,Q=200N,30°,R=300N,60°
Asavela Reply
Describe relationship between the net force exerted on an object and acceleration of the object in words
Motshidisi Reply
Newton's second law of motion states that the acceleration of an object is equal to the net force exerted on the objectdivided by the object's mass. The direction of acceleration is the same as the direction of thenet force.
Sebastian
what is close vector diagram
Lebogang
can you describe the relationship between the netf exterted on an object and A of the object for me plz
Lebogang
the are directly proportional When one increase the other will roo
Gwebzi
too
Gwebzi
and the mass is inversely proportional
Murunwa
what is an intermolecular
Senzo Reply
is the forces that act in the molecules
Lebogang

Get the best Siyavula textbooks: gr... course in your pocket!





Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 11 physical science' conversation and receive update notifications?

Ask