Electric Fields

What are atoms charges defined by?

The net sum of +ve (protons) and -ve (electrons) in the atom

When the net charge of a particle ≠ 0

It has a charge imbalance

Define Static Charges (+alternative name)

The lack of overall movement of charge in an object is static charge (electrostatics)

Define ESF

• Repulsive + Attractive force polarities

Equal magnitude of force in opposite direction:

• Repulsive = +ve

• Attractive = -ve

What are the 2 components of Coulomb’s law?

• Force between 2 charges are proportional to the product of the 2 charges (F∝Qq)

• Force is inversely proportional to the square of the distance between the point charges

What is the equation for Coulomb’s law?

F= kQq/r²

What type of quantity is Electric field strength?

• Vector quantity (shows the force the point charge experiences in the Electric field)

Define Electric field strength

The force per unit charge a small +ve would experience at that point in an electric field

Give the formula for Electric field strength (+ unit)

E= F/q

• Unit= NC^-1

What type of particles are used to measure Electric Field strength (+ why)

Small charged Point Mass’:

• Their Electric field is virtually 0, so we can accurately calculate the E.F strength of the greater charge

What is the formula for Electric field strength?

F=kQ/r²

• k = 1/4πε₀

• ε₀ = Permittivity in a vacuum

Give the axes + shape for the E.Field strength to distance graph

Describe the field lines of a +ve and -ve field

• What do the frequency of field lines show?

• More lines = Stronger E.Field = Higher charge

What is the formula for the Resultant Electric field strength for a particle in multiple fields?

• How do you find the force components?

E_Total = sqrt((E_1x + E_2x + E_3x)² + (E_1y + E_2y + E_3y)²) :

• E1x = E1 * cos(theta1)

• E1y = E1 * sin(theta1)

Electric Potential + Potential energy

Electric Potential + Potential energy

How is Work done in an Electric Field?

Work is done when a point charge is moved in an electric field

How do we know what polarity Work Done is in an electric field?

• What about EPJ

WD is -ve when a point charge is moved in the same direction as the field lines:

• -ve when it moves in the same direction as the field lines

Define EPJ

Work done to move a point charge from infinity to its position in an E-Field

Define Electric Potential

The WD per unit +ve to move a charged particle from infinity to a position in the field

Give the formula for Electric Potential

Potential= EPJ/q

• q is the point charges’ charge

Describe the E-Potential graph

• Axes

• Shape

• Gradient

• Area

• x-axis= Distance

• y-axis= Electric Potential

• Gradient = V/m → E.Field Strength

• Area = Change in Potential ΔV

+ve = Top half

-ve = Bottom half

Give the formula for work done by a point charge in an E-Field:

• Derive the change in Potential formula

• WD=qΔV

  • 1. WD=FxD

  • 2. F=Eq

  • 3. WD= EqD

  • 4. WD= qΔV

  • 5. qΔV=EqD

  • 6. ΔV=ED

What are Equipotentials?

A set of points in an Electric Field which have the same electric potential

Capacitors

Capacitors