Electric Fields Flashcards

1
Q

Define a field

A

A field is a region in which a body can experience a non-contact force.

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2
Q

What are the rules for drawing electric field lines?

A

When drawing electric fields: The lines should never cross.

The spacing of the lines represents the strength of the field.

An arrow should be drawn to show the direction of force that a positive charge would feel

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3
Q

What is a field line (electric)?

A

The path a free positive test charge follows.

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4
Q

Describe a field between two oppositely charged plates

A

Field lines run parallel, at right angles to the plates.

Field lines are evenly spaced.

At the edges of the field the lines are slightly curved.

Inside the plates is a uniform field.

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5
Q

What kind of a field is it between two oppositely charged plates?

A

Uniform field

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6
Q

What is a point charge?

A

An expression for a charged object in a situation where distances under consideration are much greater than the size of the object.

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7
Q

Sketch the electric field around a point charge?

A

Radial field with arrows pointing away. See diagram

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8
Q

Sketch the field around a negative point charge

A

Radial field with arrows pointing towards the centre of the charge.

See diagram

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9
Q

Sketch the field pattern around two positive charges

A

See diagram

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10
Q

Sketch the field pattern around a positive and negative charge

A

See diagram

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11
Q

Define electric field strength at a point in the field

A

The force per unit positive charge.

E = F/Q

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12
Q

Sketch a graph of electric field strength against separation?

What can be found from this graph?

A

See diagram

Area = Electrical potential

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13
Q

Define Coulombs law

A

The force of attraction or repulsion between two charges is proportional to the product of the charges and inversely proportional to the separation squared.

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14
Q

Sketch a graph of force against separation?

What can be found from this graph

A

See diagram

Area = work done = Electrical potential energy

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15
Q

If two forces are in the same direction, what is the resultant electric force?

A

F1 + F2

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16
Q

If two forces are in opposing direction, what is the resultant electric force?

A

F1 - F2

17
Q

If two forces are at right angles to each other, what is the resultant electric force?

A

Resolve using pythagorus.

(F12 + F22)0.5

18
Q

State the factors that affect the electric field strength between two parallel plates

A
  1. Potentail difference between the plates (directly proportional)
  2. Plate seperation (inversley proportional)
19
Q

Describe the motion of a positive charged particle moving parallel to a uniform electric field.

A

Uniform acceleration due to uniform field.

20
Q

Describe the motion of a positive charged particle moving perpendicular to a uniform electric field.

A

Motion perpendicular to the field - constant velocity.

Motion parallel to the field - constant acceleration

This causes the particle to move in a parabolic curve.

21
Q

Define electric potential difference

A

The total work done to bring a positvely charged particle from infinity to a separation r

22
Q

State the equation for electrical potential difference.

A

Ep = kQq / r

23
Q

Sketch a graph for electrical potential difference against seperation for like charges.

What can be found from this graph?

A

See diagram - like charges repel so work is done to bring them together.

There is 0 electrical potential difference at infinity.

Gradient = force

24
Q

Sketch a graph for electrical potential difference against seperation for opposite charges.

What can be found from this graph?

A

see diagram - Opposite charges attract so work is done moving them apart.

There is 0 electrical potential difference at infinity.

Gradient = Force

25
Q

Define electric potential at a point in an electric field

A

Work done per unit positive charge on a positive test charge when it is moved from infinity to that point.

V = W/Q

26
Q

What can be found from a graph of electric potential against separation?

A

Gradient = Electric field strength

27
Q

Sketch a graph of potential vs seperation when moving a positive charge towards another positve charge.

A

See top half of the diagram (positive y axis only).

Positive charges repel so work is done moving them closer together. As they move closer potential and potential energy would increase.

Potential at infinity is 0.

28
Q

Sketch a graph of potential vs seperation when moving a negative charge towards a positve charge.

A

See bottom half of the diagram (negative y axis only).

Opposite charges attract so work is done moving them further apart. As they move further apart potential and potential energy would increase.

Potential at infinity is 0.

29
Q

What do lines of equipotentail show?

A

Lines along which electric potential is constant.

30
Q

What do closer lines of equipotential show?

A

Closer equipotentials means greater potential gradient at right angles to them.

More work is needed to move a charged particle a set distance

31
Q

How is potential gradient (spacing of lines of equipotential) effected if the field is uniform?

A

Equipotentials between the plates are equally spaced parallel to the plates.

Potential gradient is constant.

32
Q

Describe the lines of equipotential for a uniform field between two parallel plates

A

Lines of equipotential are perpendiculer to the electric field and are evenly spaced.

See diagram

33
Q

Describe the lines of equipotential for a radial field from a point charge

A

Lines of equipotential are circular rings around the charge.

The spacing increases as distance from the charge increases.

See diagram

34
Q

Describe the lines of equipotential between two positive charges

A

See diagram

35
Q

Describe the lines of equipotential a positive and negative charge

A

See diagram

36
Q

State some similarities between E fields and g

A
  1. Both have infinite range
  2. Both follow the inverse square law with seperation
37
Q

State some differences between E fields and g

A
  1. E depends on charges but g depends on mass
  2. E can cause attraction or repulsion. g can only attract.