Properties of Charge: Physics

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Questions and Answers

What is the primary concept associated with an excess or deficiency of electrons in a body?

  • Electric potential
  • Electromagnetic force
  • Electric charge (correct)
  • Magnetic field

Charge can exist without mass, but mass cannot exist without charge.

False (B)

If a neutral metallic body is charged via electrostatic induction, what happens to the net charge of the inducing body?

The net charge remains unchanged.

The electrostatic force between two point charges is _ proportional to the square of the distance between them.

<p>inversely</p> Signup and view all the answers

Match the method of charging with its description:

<p>Friction = Transfer of electrons between two bodies when rubbed together. Electrostatic induction = Charge redistribution in a neutral body due to a nearby charged object. Conduction = Charge transfer through direct contact between two bodies.</p> Signup and view all the answers

According to Coulomb's law, what factor does the electrostatic interaction depend on, besides the magnitude of the charges and the distance separating them?

<p>The nature of the medium between the charges (C)</p> Signup and view all the answers

The principle of superposition states that the force on a charged particle due to multiple point charges is the algebraic sum of the forces due to individual charges.

<p>False (B)</p> Signup and view all the answers

What is the significance of a 'test charge' when defining electric field intensity?

<p>A test charge is a fictitious charge that exerts no force on nearby charges but experiences forces due to them.</p> Signup and view all the answers

In the presence of a ______, the electric field decreases compared to its value in free space.

<p>dielectric</p> Signup and view all the answers

Match the charge distribution with the appropriate expression for electric field calculation:

<p>Linear charge distribution = $E = k \int \frac{\lambda dl}{r^2}$ Surface charge distribution = $E = k \int \frac{\sigma dS}{r^2}$ Volume charge distribution = $E = k \int \frac{\rho dV}{r^2}$</p> Signup and view all the answers

What is the electric field at the center of a uniformly charged ring?

<p>Zero (C)</p> Signup and view all the answers

The electric field at a point due to an infinite line charge is directly proportional to the distance from the line charge.

<p>False (B)</p> Signup and view all the answers

Why is the electric field inside a solid conductor always zero?

<p>Charges redistribute themselves on the surface to cancel out any internal electric field.</p> Signup and view all the answers

The electrostatic interaction energy of a system of charged particles is defined as the external work required to ______ the particles from infinity to the given configuration.

<p>assemble</p> Signup and view all the answers

Match the concept with its description:

<p>Electric potential = Interaction energy of a unit positive charge at a point. Electric potential energy = Work done in bringing a charge from infinity to a point. Equipotential surface = Locus of all points having the same potential.</p> Signup and view all the answers

What is the relationship between electric field and potential gradient?

<p>$E = -∇V$ (B)</p> Signup and view all the answers

An electric dipole consists of two equal and like charges separated by a small distance.

<p>False (B)</p> Signup and view all the answers

When a dipole is placed in a uniform electric field, what is the net force on the dipole?

<p>Zero</p> Signup and view all the answers

The torque on a dipole placed in an electric field is given by $\tau = ______$, where p is the dipole moment and E is the electric field.

<p>p x E</p> Signup and view all the answers

Match the condition with the corresponding expression for torque on a dipole in an electric field:

<p>Torque is maximum = $\tau = pE$ Torque is minimum = $\tau = 0$</p> Signup and view all the answers

What is the electric potential due to a dipole at a point on its equatorial plane?

<p>Zero (D)</p> Signup and view all the answers

According to Gauss's law, the electric flux through a closed surface depends on the distribution of charges inside the surface

<p>False (B)</p> Signup and view all the answers

If a charge is placed inside a cube, what will change if the charge is shifted to a different location within the cube?

<p>Total flux will not change, but the flux linked with different faces will be different.</p> Signup and view all the answers

Electrostatic pressure on the surface of a charged conductor is directed ______ to the surface.

<p>normally</p> Signup and view all the answers

Match the quantity with relation to 'a':

<p>Angular acceleration for SHM = $α ≈ (pE/I) * θ$</p> Signup and view all the answers

Flashcards

Electric Charge

Property of matter causing electrical and magnetic effects, due to excess or deficiency of electrons.

Charge Transfer

Charge can move from one object to another through direct contact.

Charge and Mass Association

Charge cannot exist without mass, but mass can exist without charge.

Charge Quantization

Electric charge exists in discrete units, as integer multiples of the elementary charge (e).

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Charge Conservation

The total charge in an isolated system remains constant over time.

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Charge Invariance

The magnitude of charge is the same regardless of the frame of reference.

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Electrostatic Induction

Charging a body by bringing a charged object nearby, inducing charge separation.

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Conduction

Transfer of charge through direct contact between two bodies.

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Coulomb's Law

Force between two static point charges is proportional to the product of the charges and inversely proportional to the square of the distance.

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Superposition Principle

Total force on a charge is the vector sum of forces from all other charges.

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Electric Field

A region around a charge where electrical effects are perceptible.

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Electric Intensity

Force per unit charge at a point in space. Vector function.

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Electric field formula

Electric field intensity defined as force on unit test charge

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Electric Flux

How much the electric field flows through a surface.

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Gauss's Law

Relates the total electric flux through a closed surface to the enclosed charge.

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Electric potential difference

The amount of energy needed to move a unit positive charge from one location to another in the presence of an electric field.

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Equipotential Surfaces

Surfaces where the electric potential is constant. No work is done moving charges along them.

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Electric Dipole

A system of two equal and opposite charges separated by a small distance.

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Dipole Moment

Product of charge and separation; direction is from negative to positive charge.

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Dipole Oscillation

A measure of restoring torque on a dipole in electric field

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Electrostatic Pressure

Force per unit area on a charged conductor's surface.

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Study Notes

  • Charge is a property of matter, creating electrical and magnetic phenomena
  • Excess or deficiency of electrons in a body is the concept of charge
  • SI unit of charge is ampere x second [AT]
  • Practical units for charge are ampere x hour (=3600 C) and faraday (= 96500 C)
  • Millikan determined the quantum of charge equals the charge of an electron using the "Highest Common Factor" method
  • 1 C equals 3 x 10^9 state coulombs, 1 absolute coulomb is 10 C, and 1 Faraday equals 96500 C

Specific Properties of Charge

  • Charge is scalar, indicating electron excess/deficiency
  • Charge is transferable through contact between bodies
  • Charge must have mass to exist, though mass can exist without charge
  • Charge presence indicates mass existence
  • Body mass changes during charging
    • Positive charge decreases mass
    • Negative charge increases mass
  • Electric charge is quantized
    • Free charges have integral multiples of a basic unit, e
    • A body's charge is given by q = ne
    • 'n' is a positive or negative integer
  • A quantum of charge is the charge of a proton or electron
  • Charge of a proton = (-) charge of an electron = 1.6 x 10^-19 C
  • Charge is conserved
    • In isolated systems, total charge remains constant, even if individual charges change
    • Charge can neither be created nor destroyed
    • Verified true in all chemical, atomic, and nuclear reactions with no exceptions
  • Charge is invariant
    • Charge remains constant regardless of the speed of the body
  • Attractive and repulsive properties:
    • Similar charges repel, while dissimilar ones attract

Methods of Charging

  • Friction involves electron transfer when rubbing objects together
  • Electrostatic induction attracts opposite charges and repels similar charges when a body approaches a metallic neutral body, resulting in a negative side and a positive side which is called electrostatic induction
    • The 4 steps of induction are approaching the body, grounding, disconnecting from ground, removing the charged body
  • During induction:
    • The inducing body doesn't gain/lose charge
    • Induced charge is always opposite
    • Occurs in conducting/non-conducting bodies but not particles
  • Conduction is charge transfer via contact
    • Contact between charged and uncharged bodies causes electron transfer
    • Transferring some charge from charged to uncharged body
    • Gained charge is always lesser than the initial

Coulomb's Law

  • Electrostatic force between static point charges is:
    • Proportional to the charge product
    • Inversely proportional to the distance square
    • Acts along the line connecting the them
  • Electrostatic interaction depends on the medium and can be calculated as
  • F = ke (q1q2/r^2) where ke is Coulomb's constant or electrostatic force constant, k = 9 x 10^9 Nm^2/C^2
  • In vector form, the force on q1 due to q2 is kq1q2/r^2 r^, where r^ is the unit vector from q1 to q2
  • In terms of position vectors, the force between two charges is proportional to these vector values
  • The principle of superposition states that when multiple charges interact, the total force on a charge is the vector sum of other forces individually
  • Coulomb's law is based on physical observations
  • Experiments reveal universal nature

Important laws and concepts

  • The force is a two body interaction
    • Electric force between two point charges are independent
    • So the principle of superposition is valid
    • The net force in free space or infinite is F = q1q2/4πεr²
  • Dielectric constant (K) numerically equals the ratio of force on two point charges in free space to that in medium upto infinity
  • F/F' = ε/ε₀ = K
  • The law expresses force between two resting point charges
  • Apply to extended bodies of finite size, assuming the whole charge concentrates at its centre for spherical charged bodies

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