Electric Fields - Newtonian World

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  • Created by: lucysnell
  • Created on: 28-01-16 16:47

What creates an electric field?

  • 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
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Coulombs Law

  • 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
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Electric Field Strength

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
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Radial Fields

  • 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
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Uniform Fields

  • 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=  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
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Charged Particles in Uniform Fields

  • 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
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Similarirties - Grav Fields and Electric Fields

  • 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
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Differences - Grav Fields and Electric Fields

  • 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
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