Electric Charges Flashcards
Define
electrostatics
Electric charge
Electrostatics is that branch of physics that deals with electric charges at rest
Electric charge is that characteristic property of electrons and protons or other charged bodies responsible for the electric force between them.it may be positive or negative
What property is responsible for gravitational force and electric force
Mass responsible for gravitational force and charge for electric force
What is elementary or fundamental charge in nature?
What is S I unit of charge ?
The smallest charge that can be added or removed from a body . It is the charge of an electron and is equal to 1.610^-19. Is actually 1.6021810^-19 C
Coulomb represented C
What is electrification ? Mention the methods…
The process of charging a body by the loss or gain of electrons.
By friction
By conduction
By induction
Explain electrification by friction
When 2 bodies are rubbed together at the various points of contact, electrons are transferred from one body to the other. The body that loses electrons gets positively charged and the one that gains electrons gets negatively charged. The magnitude of charge gained by both bodies are equal. The bodies are insulators . The bodies are said to be charged by friction
Glass +ve and silk -ve ebonite -ve and wool +ve
Explain conduction
A good conductor can be charged by touching it with a charged body . The process is known as charging by conduction . The charge acquired by the body is of the same nature as that of the charging body.
Explain induction
A good conductor can also be charged by placing it near a charged body. This process is known as charging by induction.the nature of the induced charge is always opposite to that of the charging body.
Define conductors
Define insulators or dielectrics
Give examples
Conductors are materials that allow electric charges to flow through them freely. Charges on conductor are distributed all over the surface.metals are good electrons as they contain large number of free electrons
Insulators are materials which do not allow the flow of charges through them. The charge on insulator remains localised. Ebonite wood mica glass plastic rubber
How are charges distributed on the surface of a conductor
What is action of points.
Distribution of charges on surface of a conductor depends on the shape of the conductor. They tend to accumulate in abundance at pointed ends edges and corners where radius of curvature is min.
Due to this the excess charges are released to the surroundings. This is known as action of points.
Why do charges distribute themselves over the surface of conductor?
Why are they evenly distributed over a spherical conductor?
So that force of repulsion between them is minimum and potential energy of conductor is minimum.
Because its curvature is uniform.
Define surface density of charge
Surface density, σ , is the charge per unit area on the surface.
It increases with the curvature of the surface and is inversely proportional to the square of the radius of curvature . SI unit is coulomb per metre squared C/m^2
For a spherical conductor of charge q and radius r
σ = q/4π r^2
Define linear density of charge
Linear density of charge λ is the charge per unit length.
SI unit is coulomb per metre
C/m
What are the properties of charges
Like charges repel . Unlike charges attract.
Charged bodies attract light uncharged bodies
Charge resides on the outer surface of the charged conductor.
Its a scalar and derived quantity SI unit C
Charge is additive in nature
Charge is independent of the velocity of the body. Unaffected by motion is invariant.
Accelerated charges radiate energy in the form of EMW
Can’t exist without mass. Mass can exist without charge
Charge is conserved
Charge is quantised
What is the law of electrical charges
Like charges repel each other while unlike charges attract each other
What do you mean by charge is additive?
The net charge of the system is the algebraic sum of the charges comprising the system
What do you understand by charge is conserved?
Stat the law of conservation of charges
According to the law of conservation of charge, the algebraic sum of the positive and negative charges in an isolated system remains the same.
I.e. when charge is created or destroyed it is in equal and opposite amounts
Is seen in nuclear reactions radioactive decay pair production etc.
What do you mean by charge is quantised?
The charge q acquired by a body in any process is an integral multiple of the elementary charge e
I.e. q = +/- ne where n = 1,2,3…
Charge exists in discrete packets not a continuous amount.
What are quarks what is the charge on them?
What is the charge on proton and electron
The elementary particles of charge (1/3)e and (2/3)e whose existence has recently been postulated are called quarks.
Charge on proton/electron is +/- 1.6*10^-19 C
State coulombs law or coulombs inverse square law
Gives magnitude of electrical force between 2 stationary charged particles
According to coulombs law , the electrostatic force of attraction or repulsion between 2 stationary point charges is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them
What is coulomb constant or electrostatic force constant ? What does it depend on
It is a positive constant of proportionality . Depends on
1. The system of units
2. The medium in which the charges are situated .
Denoted by k
Value is 8.9875 * 10^9
Taken as 9*10^9
What is the direction of force between 2 stationary charges?
The force acts along the straight line joining the 2 charges.
It is repulsive between like charges and attractive between unlike charges.
What is coulomb?
Coulomb is the SI unit of charge..
1 coulomb of charge is that charge which when placed at rest in vacuum at a distance of 1 metre from an equal and similar stationary charge repels it and is repelled by it with a force of 9 * 10^9
What are the limitations of coulombs law?
- Coulombs law holds good for stationary point charges only .
- It is not universal as it depends on the properties of the intervening medium.
Define dielectric constant
Dielectric constant or relative permittivity of a medium can be defined as the ratio of electrostatic force between 2 point charges separated by a certain distance in free space to the electrostatic force between the same 2 point charges separated by the same distance in the medium
It is also the ratio of permittivity of free space to the absolute permittivity of the medium.
What is dielectric constant of vacuum and air.
What is the effect of a dielectric medium on the electrostatic force?
Vacuum K = 1
Air K = 1.00059
For all other media K > 1. It follows that F < F0
Hence presence of dielectric reduces the coulomb force between the 2 charges
What are the important results of coulombs law in vector form
- The force between the charges is mutual
- Force between any two charges is not affected by the presence of other charges in the neighbourhood
- Principle of superposition holds good for coulomb electrostatic force
- Equilibrium of a charged particle under the action of Coulombian forces alone can never be stable
What do you understand by electrostatic force between 2 charges is mutual
The forces exerted by the charges on each other are equal in magnitude and opposite in direction. These forces form an action reaction pair according to newton’s third law of motion
How does principle of superposition hold good for coulomb electrostatic force?
When a number of forces are interacting the net force on a given charge is the vector sum of the forces exerted on it by all other charges
What are the similarities between electrostatic force and gravitational force?
They act along the line joining the centres of the two interacting bodies , charge or mass. They are central forces
Vary inversely as the square of the distance between the two interacting bodies. They obey inverse square law
Are conservative forces. Work done by them is independent of the path
Operate in vacuum as well as material media between the bodies
Obey principle of superposition
What are the differences between electrostatic and gravitational forces?
Es F is between two particles. G F is between two masses
Es F may be attractive or repulsive. G F is always attractive
Es F is not universal. G F is universal
Es F is much stronger than G F
