Electric fields Flashcards

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1
Q

Name some basic rules of charges and electric fields

A
  • Electric charge,Q, is measured in coulombs(C) and can be either positive or negative.- Opposite charged particles attract each other.Like charges repel.- If a charged objet is placed in an electric field, then it will experience a force. - Any object with charge has an electric field around it.
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2
Q

What is the equation for Coulomb’s law?

A

F = kQ1Q2/r2

Where K = 1/4πE

E = permittivty of material between charges.

r = is the distance between the charges.

  • The force on Q1 is equal and opposite to the force on Q2.
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3
Q

What is the definition of electric field strength, E?

A

Electric field strength, E is defined as the force per unit positive charge - the force that a charge of 1+ C would experience if it was placed in the electric field.

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4
Q

What is the equation for electric field strength?

A

E=F/q

  • F is the force on a charge q.
  • E is a vector pointing in the direction that a positive charge would move.
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5
Q

Draw the field lines around a positive charge and the field lines around a negative charge.

A
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6
Q

What is the equation for electric field strength at diffirent points along a radial field?

A

E = kQ/r2

  • r is the distance from a point charge.
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7
Q

Draw the graph of E against r. (Where r is the distance from a point charge Q.)

  • State what the relationship is between the two variables.
  • What the area under the graph is.
A
  • The relationship between E and r is an inverse square one.
  • The area under the graph is the electric potential.
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8
Q

What is electric potential energy?

A

The work that would need to be done to move a small charge,q, from infinity to a distance r away from a point charge, Q.

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9
Q

What is the equation for electric potential energy.

A

E = kQq/r

  • Q is a point charge and q is another charge.
  • In a repulsive force field(Q and q are both positive) you have to do work against the repulsion to bring q closer to Q. The charge q gains potential energy as r decreases.
  • In an attractive field the charge q gains potential energy as r increases.
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10
Q

Draw the graph of the electric potential energy of a charge q when in a repulsive field and when in an attractive field at distances r from the source.

A
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11
Q

What is electric potential, V.

A

Electric potential, V, is electric potential energy per unit positive charge.

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12
Q

What is the equation for electric potential.

A

V = kQ/r

  • V is measured in volts
  • As with E, V is positive when the force is repulsive, and negative when the force is attractive.
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13
Q

Draw the graph of electric potential , V, against distance for a repulsive force.

  • What does the gradient of the graph tell you?
A

The gradient of a tanget gives the field strength.

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14
Q

How can a uniform field be made?

A

A uniform field can be produced by connecting two parallel plates to the opposite poles of a battery.

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15
Q

How can the field strength, E, be calculated from a uniform field between two plates?

A

Field strength E is the same at all points between the two plates and is given by:

E= V/d

V is the potential diffirence between the plates and d is the distance between them.

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