Capacitors Flashcards
What is capacitance?
The capacitance of a conductor is defined as numerically equal to the quantity of charge required to raise the potential of the conductor by one unit in the given environment
What does the capacitance of a conductor depend on?
- The size and shape of the conductor
- The dielectric medium surrounding the conductor
- The presence of nearby conductors
Does not depend on material of the conductor
What is unit of capacitance? Define.
F - farad
The capacitance of a conductor is said to be one farad if one coulomb of charge raises its potential by one volt in the given environment
What is a capacitor?what are the types?
A capacitor is an electrical device for storing large quantity of charge and hence electrical energy.
Parallel plate
Spherical
Cylindrical
What is the capacitance of a capacitor? What does it depend on?
Capacitance of a capacitor is the ratio of the magnitude of the charge on either conductor to the potential difference between the conductors forming the capacitor. Depends on Shape and size of conductors Separation between the conductors Dielectric medium between the conductors
How can you increase the capacitance of a parallel plate capacitor ?
Increasing area of the plate
Decreasing distance between the plates
Using a medium of higher dielectric constant between the plates
Describe the electric field between the plates of a parallel plate capacitor
The electric field is localised between the oppositely charged plates of the capacitor. The electric field is uniform throughout the region between the plates only when the distance between them is much lesser than the linear dimension of the plates. Otherwise the field will not be uniform near the outer boundary of the plates. The field lines are curved near the edges. This effect is called fringing of the field or edge effect.
Define dielectric constant in terms capacitance
The dielectric constant or relative permittivity of a medium may be defined as the ratio of the parallel plate capacitor with the given dielectric medium between the plates to the capacitance if the same capacitor with air as the dielectric medium between the plates
How do you increase the capacitance of a spherical capacitor
Use spherical conductors of larger radii
Decrease separation between the conductors
Using medium of higher dielectric constant between the conductors
Increase the capacitance of cylindrical capacitor
Increase length of capacitor
Decrease separation between the conductors
Using medium of higher dielectric constant between the conductors
What is equivalent capacitor?
The equivalent capacitor of a combination of capacitors is that single capacitor which effectively replaces the combination and will store the same amount of charge for a given potential difference as the combination does.
The capacitance of the equivalent capacitor is called equivalent / effective capacitance.
What is a variable capacitor?
A variable capacitor is one in which the effective area of the plates and hence the capacitance of the capacitor can be varied between certain limits?
What is super cap?
Super capacitors of modest size having a large capacitance of the order of one farad .they are used as back up voltage sources for computers
What is a series combination of capacitors?
Two or more capacitors are said to be in series when they are connected end to end between two given points so that on applying a potential difference across the combination magnitude of charge on each capacitor is the same
What is a parallel combination of capacitors
Two or more capacitors are said to be in parallel when they are connected between the same two points so that in applying a potential difference across the combination the potential difference across each combination is the same.
What are the uses of capacitors?
Store electrical charge and energy
As potential dividers
To eliminate sparking as in an induction coil
In ignition systems of automobile engines
In radio circuits for tuning
In electronic power supply systems to reduce the pulsations
To determine very high resistances of the order of mega ohm
To separate radioactive radiations
To deflect the electron beam in a CRO
In generation and detection of electromagnetic waves.
