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Physics paper 2 > Electric fields > Flashcards

Electric fields Flashcards

1
Q

Does any charged object have an electric field around it?

A

Yes

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2
Q

What is an electric field?

A

A region where charged objects will experience a non-contact force.

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3
Q

What is the unit for electric charge?

A

Coulombs (C)

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4
Q

What is the symbol for electric charge?

A

Q

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5
Q

Can charge be positive and negative?

A

Yes

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6
Q

Oppositely charged particles…

A

Attract

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7
Q

Like charges…

A

Repel

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8
Q

What happens when a charged object is placed in an electric field?

A

It experiences a force.

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9
Q

State Coulomb’s law.

A

The magnitude of the force between two charged objects is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
F = 1/4πε₀ x Q₁Q₂/r²

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10
Q

Give the equation for Coulomb’s law.

A

F = 1/4πε₀ x Q₁Q₂/r²

Where:
* F = Force (N)
* ε₀ = Permittivity of free space = 8.85 x 10^-12 F/m
* Q = Charge (C)
* r = Distance between charges (m)

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11
Q

What type of law is Coulomb’s law?

A

Inverse square law
* Since F ∝ 1/r²

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12
Q

What is electric field strength?

A

The force per unit positive charge exerted at a certain point in an electric field.

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13
Q

What is the symbol for electric field strength?

A

E

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14
Q

What is the unit for electric field strength?

A

N/C

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15
Q

What is the equation than defines electric field strength?

A

E = F/Q

Where:
* E = Electric Field Strength (N/C)
* F = Force (N)
* Q = Charge (C)

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16
Q

Is electric field strength a scalar or vector quantity?

A

Vector

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17
Q

For 2 positive parallel plates, which way do the field lines point?

A

From the plate with more positive voltage to the plate with less positive voltage.

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18
Q

Give the equation for the electric field strength around a point charge.

A

E = 1/4πε₀ x Q/r²

Where:
* E = Electric field strength (N/C)
* ε₀ = Permittivity of free space = 8.85 x 10^-12 F/m
* Q = Charge of point charge
* r = Distance from the point charge

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19
Q

How can a uniform electric field be produced?

A

Connecting two parallel plates to opposite poles of a battery.

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20
Q

What can be said about electric field strength in a uniform electric field?

A

It is the same at all points.

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21
Q

What is the equation that defines electric field strength in a uniform electric field?

A

E = V/d

Where:
* E = Electric field strength (N/C or V/m)
* V = Potential difference (change) between plates (V)
* d = Distance between plates (m)

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22
Q

What is are the units for electric field strength in a uniform field?

A

V/m-1 or NC-1

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23
Q

What can a uniform electric field be used for? How?

A

-Determining whether a particle is charged.
-If a particle curves in the same direction as the field lines, it is positively charged
-If a particle curves in the opposite direction as the field lines, it is negatively charged

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24
Q

What is a particle’s curved path in an electric field called?

A

Parabola

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25
Q

What is absolute electric potential?

A

The electric potential energy that a unit positive charge would have at a point in an electric field.

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26
Q

What effects electric potential?

A

Size of charge creating the electric field and distance from the charge.

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27
Q

What is the symbol for electric potential?

A

V

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28
Q

What are the units for electric potential?

A

Volts (V)

29
Q

Give the equation for electric potential around a point charge.

A

V = 1/4πε₀ x Q/r

Where:
* V = Electric potential (V)
* ε₀ = Permittivity of free space = 8.85 x 10^-12 F/m
* Q = Charge of point charge
* r = Distance from the point charge

30
Q

When is V positive around a point charge?

A

When Q is positive. Force is repulsive

31
Q

When is V negative around a point charge?

A

When Q is negative. Force is attractive

32
Q

When is the magnitude of the electric potential around a point charge the greatest?

A

On the surface of the charge.

33
Q

What is electric potential (V) equal to at infinite distance?

A

0V

34
Q

What equation relates electric field strength with the change in electric potential around a point charge?

A

E = ΔV / Δr

Where:
* E = Electric field strength (N/C or V/m)
* ΔV = Electric potential difference (V)
* Δr = Change in distance from the charge (m)

35
Q

What is electric potential difference?

A

The energy needed to move a unit (positive(?)) charge between two points.

36
Q

What equation gives the work required to move a charge through an electric potential difference?

A

ΔW = Q x ΔV

Where:
* ΔW = Work done (J)
* Q = Charge being moved (C)
* ΔV = Electric potential difference (V)

37
Q

What is the symbol for electric potential difference?

A

ΔV

38
Q

Derive the formula for work done in moving a charge through an electric potential difference.

A

E = F / Q = ΔV / d
Fd = QΔV
ΔW = QΔV

39
Q

What are equipotentials in electric fields?

A

Lines that show all points of equal potential in the electric field.

40
Q

What shape are equipotentials around a point charge?

A

Spherical

41
Q

What do equipotentials around a point charge and between two parallel plates look like?

A
42
Q

What are the Inverse square laws that are seen in both electric and gravitational fields?

A

Force between two masses / point charges
* Field strength around a mass / point charge

43
Q

What is the one important difference between electric and gravitational fields?

A

Gravitational fields are always attractive, whereas electric forces can be attractive or repulsive.

44
Q

What is earthing?

A

When electrons move to or from the earth to balance charges on charged objects

45
Q

What happens, when charge is transferred between objects, if one of the objects is an insulator?

A

The charge can build up

46
Q

What do electric field lines show?

A

The direction of the force that would be felt by a small positive charge

47
Q

What do equally spaced field lines show?

A

A uniform field

48
Q

Where do field lines stop and start?

A

Either on a charge or at infinity

49
Q

What is the equation for electric field strength?

A

E = F / Q

50
Q

What is field strength?

A

The force per unit (positive) charge exerted by the field

51
Q

What are the units for electric field strength?

A

N C-1

52
Q

Summary of Coulomb’s law?

A

The force between two point charges is

∙ directly proportional to each of the charges Q1 and Q2

∙ inversely proportional to the square of their separation

53
Q

What is the equation for Coulomb’s law?

A

F = kQ1Q2 / r²

(Not given on formula sheet)

54
Q

What does k depend on in F=kQ1Q2 / r²?

A

The permittivity of the substance separating the charges

55
Q

What permittivity does every insulating material have?

A

Greater than the permittivity of free space

56
Q

What equation do you get when the electric field and coulombs law equation are combined?

A

E = kQ / r²

(Not given on formula sheet)

57
Q

What does k equal in E = kQ / r²?

A

1 / 4πℇ

58
Q

How can the strength of the uniform field between parallel plates be made stronger?

A

∙ increase p.d. across plates

∙ moving plates closer together

59
Q

What is the equation for the force on an electron in an electron beam, and why is this?

A

∙ F = e V / d

(as E=V/d and force on an electron charge is F=Ee

60
Q

What is the shape of the path when electron beams are deflected?

A

Curved, as the force (F=eV/d) is constant

61
Q

What is the difference between electric and gravitational fields, in terms of their definition?

A

∙ electric - force per unit charge

∙ gravitational - force per unit mass

62
Q

What is the difference between electric and gravitational fields, in terms of their force equation?

A

∙ electric - F=Eq

∙ gravitational - F=mg

63
Q

What is absolute electric potential calculated using?

A

V = 1/4πℇ x Q/r

64
Q

What does r equal in V = 1/4πℇ x Q/r?

A

Distance from the charge Q

65
Q

When will two points in an electric field have an electric potential difference between them?

A

If they have a different absolute electric potential

66
Q

What is electric potential difference?

A

The energy required to remove a unit charge between two points in an electric field that have a different electric potential

67
Q

Where are field lines in relation to equipotential lines?

A

Perpendicular

68
Q

When is electric potential zero?

A

At infinity

Physics paper 2 (7 decks)

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