Electric Fields - Newtonian World

• An object with charge has an electric field spreading out infinitely around it

• Electric charge (Q) is meausred in Coulombs (C)

• Opposite charges attract. Like charges repel

• If a charged particle is placed in an electric field, it will experience a force

• Coulombs Law is an inverse square law

• Define coulombs law: The force experienced between two charged particles is directly proportional to the product of the charges on them and inversely proportional to the square of the distance between them.

• The force on Q1 is equal and opposite to the force on Q2

Electric field strength is defined as: The force per unit positive charge on a small positive test charge placed at a point in the field

• E=F/q

• Field strength depends on where you are in the field

• A point charge behaves as if charge is concentrated in the centre

• The electric field spreads out around the point charge in a radial field

• E is the force per unit positive test charge

• In a radial field, the electric field strength (E) depends on the distance, r, from the charge, Q

• E is proportional to r^2

• Field strength of a radial field decreses the further away you get from the charge, Q

When drawing radial fields around a point charge remeber:

• You must draw at least eight electric fields lines
• Electric fields lines ALWAYS go from positive to negative
• Always indicate the direction of the electric field with arrows

• In a uniform electric field, the field strength is the same everywhere
• A uniform field can be produced by connecting two parallel plates to opposite poles of a battery

E=V/d

E=  electric field strength

V= potential difference between the two plates

d= distance between the two plates

When drawing uniform electric fields remember to:

• Use a ruler - electric field lines are parallel and evenly spaced
• The closer together the lines are - the stronger the electric field

• Charged particles move like projectiles through uniform electric fields

• Charged particles experience a constant force parallel to the direction of travel

• A +vely charged particle will move in the same direction as the electric field lines

• A -vely charged particle (electron) will experience a force in the opposite direction to the electric field lines

• If a particles velocity has a component acting at right angles to the motion, it will continue at the same velocity (N1)

• The effect of constant acceleration in one direction and constant velocity in the other results in a parabola shape

• They are both force per unit something

• They are both inverse square laws

• A point mass creates a radial grav field - a point charge creates a radial electric field

• Gravitational fields are always attractive, whereas electric fields can be attractive OR repulsive

• Objects can be shielded from electric fields but never from grav fields

• The medium between point charges affects the size of the force (epsilon zero) but the medium between masses in a gravitational field does not affect the size of the force on the masses