# 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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• 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=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
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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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