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Physics Chp 6 > Electric Fields > Flashcards

Electric Fields Flashcards

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1
Q

What does a charged object create?

A

An electric field around itself

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2
Q

What can an electric field be defined as?

A

A region where an electric charge experiences a force

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3
Q

What happens if other charges enter an electric field and what does the direction depend on?

A

They will experience an electric force, attracting or repelling them from the object. The direction of this force depends on whether the charges are the same or opposite

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4
Q

What is the force experienced by other charges entering an electric field?

A

Attractive or repulsive

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5
Q

What do opposite charges do?

A

Attract each other

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6
Q

Who do like charged do?

A

Repel each other

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7
Q

Describe what an electric field looks like

A

Arrows point towards the negative charge / away from the positive charge

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8
Q

For a point outside a spherical conductor, what may the charge of the sphere be considered to be?

A

A point charge at its centre

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9
Q

What is a uniform spherical conductor?

A

One where its charge is distributed evenly

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10
Q

What are the electric field lines around a spherical conductor identical to?

A

Those around a point charge

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11
Q

What is an example of a spherical conductor?

A

A charged sphere

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12
Q

What are the field lines for a spherical conductor and what does their direction depend on?

A

Radial and their direction depends on the charge of the sphere

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13
Q

If the spherical conductor is positively charged, where are the field lines directed?

A

Away from the centre of the sphere

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14
Q

If the spherical conductor is negatively charged, where are the field lines directed?

A

Towards the centre of the sphere

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15
Q

What is the direction of electric fields represented by?

A

Electric field lines

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16
Q

Where are electric fields directed?

A

From positive to negative (away from positive charge and towards negative charge)

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17
Q

How does a radial field spread?

A

Uniformly to or from the charge in all directions, e.g. the field around a point charge or sphere

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18
Q

What are the electric field lines around a point charge?

A

Directly radially inwards or outwards

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19
Q

For a point charge, if the charge is positive the fields linear are …

A

Radially outwards

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20
Q

For a point charge, if the charge is negative the fields linear are …

A

Radially inwards

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21
Q

What does a uniform electric field have?

A

The same electric field strength throughout the field, e.g. the field between oppositely charged parallel plates

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22
Q

How is a uniform electric field represented?

A

By equally spaced field lines

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23
Q

What does a non-uniform electric field have?

A

Varying electric field strength throughout

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24
Q

How is the strength of an electric field determined ?

A

By the spacing of the field lines

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25
Q

How is a stronger field represented?

A

By field lines closer together

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26
Q

How is a weaker field represented?

A

By field lines further apart

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27
Q

What is a radial field considered and what does this mean?

A

A non-uniform field, so the electric field strength E is different depending on how far you are from a charged particle

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28
Q

What is an electric field?

A

A region of space in which an electric charge ‘feels’ a force

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29
Q

What is the electric field strength at a point defined as?

A

The electrostatic force per unit positive charge acting on the charge at that point

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30
Q

What is the equation for electric field strength (NC-1)?

A

Electrostatic force on the charge (N) / charge (Q)

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31
Q

Why is it important to use a positive test charge (in the definition of electric field strength)?

A

Because it determines the direction of the electric field

32
Q

What is a test charge?

A

A charge with a magnitude so small that placing it at a point has a negligible affect on the field around it

33
Q

Is electric field strength a scalar or vector quantity?

A

Vector quantity

34
Q

What is the magnitude of the electric field strength in a uniform field between two charged parallel plates defined as (Vm-1)?

A

Potential difference between the plates (V) / Separation between the plates (m)

35
Q

What does the equation E= V/d show?

A

The greater the voltage between the plates, the stronger the field
The greater the separation between the plates, the weaker the field

36
Q

Why can the equation E= V/d not be used for the E around a point charge?

A

Because the field is radial

37
Q

How do you derive E= V/d?

A

When 2 points in an electric field have a different potential, there is a potential difference between them. To move a charge across the potential difference, work needs to be done. Two parallel plates with a potential difference deltaV across them creates a uniform electric field

DeltaV = W/Q

W = DeltaV x Q

W = F x d

F x d = DeltaV x Q

F / Q = DeltaV / d

Since E = F / Q, E = DeltaV / d

38
Q

What do all charged particles produce?

A

An electric field around them

39
Q

What is the electrostatic force between two charges defined by?

A

Coulomb’s law

40
Q

What does Coulomb’s law state?

A

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of their separation

41
Q

What is the equation relating to Coulomb’s law?

A

Force = (Charge 1 x charge 2) / (4 x pi x E0 x distance^2)

42
Q

What is the inverse square law?

A

1 / r^2 relation

43
Q

What does the inverse square law mean?

A

When the separation of two charges doubles, the electrostatic force between them reduces by (1/2)^2 = 1/4

44
Q

What is E0?

A

The permittivity of free space (and refers to charges in a vacuum)

45
Q

What is ε?

A

A measure of the resistance offered by a material in creating an electric field within in

46
Q

What is the product Qq of like and opposite charges?

A

Like: positive

Opposite: negative

47
Q

What is the sign of the force of like and opposite charges?

A

Like: positive

Opposite: negative

48
Q

What is the difference between like and opposite charges?

A

Opposite attract

49
Q

What does the electric field strength describe?

A

How strong or weak an electric field is at that point

50
Q

What type of field does a point charge produce?

A

A radial

51
Q

What does a charged sphere act like?

A

A point charge

52
Q

What is the equation for: electric field strength E at a distance r due to a point charge Q (in free space)?

A

E= Q/4 x pi x E0 x r^2

Q - point charge producing the radial electric field

r - distance from the center of the charge

53
Q

What does the equation E= Q/4 x pi x E0 x r^2 show?

A

Electric field strength in a radial field is not constant

As the distance from the charge r increases, E decreases by a factor of 1/r^2

54
Q

Is electric field strength a vector or scalar quanitity?

A

Vector quantity

55
Q

What sign is the electric field strength for positive and negative charges?

A

Positive: positive, points away from the center of the charge

Negative: negative, points towards the center of the charge

56
Q

What is the equation E= Q/4 x pi x E0 x r^2 analogous to?

A

The gravitational field strength around a point mass

57
Q

What is permittivity?

A

A measure of how easy it is to generate an electric field in a certain material

58
Q

What is the relative permittivity εr sometimes known as?

A

The dielectric constant

59
Q

What is relative permittivity defined as?

A

The ratio of the permittivity of a material to the permittivity of free space

60
Q

What is the equation for relative permittivity

A

Er = E / E0

Er - relativity permittivity

E - permittivity of a material

E0 - permittivity of free space

61
Q

Why does relative permittivity have no units?

A

Because its a ratio of two values with the same unit

62
Q

What is a dielectric?

A

A substance that is a poor conductor of electricity but a good supporter of electric fields

63
Q

What happens when the polar molecules in a dielectric align with the applied electric field from the plates?

A

They each produce their own electric field and this electric field opposes the electric field from the plates

64
Q

What does a larger opposing electric field from the polar molecules in the dielectric mean?

A

A larger permittivity - the permittivity is how well the polar molecules in a dielectric align with an applied electric field

65
Q

As the opposing electric field reduces the overall electric field, what does this do to the potential difference and capacitance?

A

The potential difference between the plates decreases, therefore the capacitance of the plates increases

66
Q

What is the equation for capacitance?

A

C = A x E0 x Er / d

A - cross sectional area of the plates

d - separation of the plates

Er - relative permittivity of the dielectric between the plates

67
Q

Capacitor plates are generally square, so if it has a length of L on all sides what will the cross sectional area A be?

A

L^2?

68
Q

What causes a charged particle in an electric field to move?

A

It will experience a force on it causing it to move

69
Q

What happens if a charged particle remains still in a uniform electric field?

A

It will move parallel to the electric field lines (along or against the field lines depending on its charge)

70
Q

What happens if a charged particle in motion travels initially perpendicular through a uniform electric field (e.g. between two charged parallel plates)?

A

It will experience a constant electric force and travel in a parabolic trajectory

71
Q

What does the direction of parabolic trajectory depend on?

A

The charge of the particle

Positive charge will be deflected towards the negative plate and negative charge will be deflected towards the positive plate

72
Q

In a uniform electric field, does the force on the particle change?

A

No, it stays the same at all points and is always in the same direction

73
Q

How does an uncharged particle travel through a uniform electric field (parallel plates)?

A

It experiences no force in an electric field and therefore travels straight through the plates undeflected

74
Q

What does the amount of deflection depend on?

A

Mass, charge and speed

75
Q

How does mass affect deflection?

A

The greater the mass, the smaller the deflection and vice versa

76
Q

How does charge affect deflection?

A

The greater the magnitude of the charge of the particle, the greater the deflection and vice versa

77
Q

How does speed affect deflection?

A

The greater the speed of the particle, the smaller the deflection and vice versa

Physics Chp 6 (2 decks)

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