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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
What is absolute electric potential?
The electric potential energy that a unit positive charge would have at a point in an electric field.
26
What effects electric potential?
Size of charge creating the electric field and distance from the charge.
27
What is the symbol for electric potential?
V
28
What are the units for electric potential?
Volts (V)
29
Give the equation for electric potential around a point charge.
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
When is V positive around a point charge?
When Q is positive. Force is repulsive
31
When is V negative around a point charge?
When Q is negative. Force is attractive
32
When is the magnitude of the electric potential around a point charge the greatest?
On the surface of the charge.
33
What is electric potential (V) equal to at infinite distance?
0V
34
What equation relates electric field strength with the change in electric potential around a point charge?
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
What is electric potential difference?
The energy needed to move a unit (positive(?)) charge between two points.
36
What equation gives the work required to move a charge through an electric potential difference?
ΔW = Q x ΔV Where: * ΔW = Work done (J) * Q = Charge being moved (C) * ΔV = Electric potential difference (V)
37
What is the symbol for electric potential difference?
ΔV
38
Derive the formula for work done in moving a charge through an electric potential difference.
E = F / Q = ΔV / d Fd = QΔV ΔW = QΔV
39
What are equipotentials in electric fields?
Lines that show all points of equal potential in the electric field.
40
What shape are equipotentials around a point charge?
Spherical
41
What do equipotentials around a point charge and between two parallel plates look like?
42
What are the Inverse square laws that are seen in both electric and gravitational fields?
Force between two masses / point charges * Field strength around a mass / point charge
43
What is the one important difference between electric and gravitational fields?
Gravitational fields are always attractive, whereas electric forces can be attractive or repulsive.
44
What is earthing?
When electrons move to or from the earth to balance charges on charged objects
45
What happens, when charge is transferred between objects, if one of the objects is an insulator?
The charge can build up
46
What do electric field lines show?
The direction of the force that would be felt by a small positive charge
47
What do equally spaced field lines show?
A uniform field
48
Where do field lines stop and start?
Either on a charge or at infinity
49
What is the equation for electric field strength?
E = F / Q
50
What is field strength?
The force per unit (positive) charge exerted by the field
51
What are the units for electric field strength?
N C-1
52
Summary of Coulomb’s law?
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
What is the equation for Coulomb’s law?
F = kQ1Q2 / r² (Not given on formula sheet)
54
What does k depend on in F=kQ1Q2 / r²?
The permittivity of the substance separating the charges
55
What permittivity does every insulating material have?
Greater than the permittivity of free space
56
What equation do you get when the electric field and coulombs law equation are combined?
E = kQ / r² (Not given on formula sheet)
57
What does k equal in E = kQ / r²?
1 / 4πℇ
58
How can the strength of the uniform field between parallel plates be made stronger?
∙ increase p.d. across plates ∙ moving plates closer together
59
What is the equation for the force on an electron in an electron beam, and why is this?
∙ F = e V / d (as E=V/d and force on an electron charge is F=Ee
60
What is the shape of the path when electron beams are deflected?
Curved, as the force (F=eV/d) is constant
61
What is the difference between electric and gravitational fields, in terms of their definition?
∙ electric - force per unit charge ∙ gravitational - force per unit mass
62
What is the difference between electric and gravitational fields, in terms of their force equation?
∙ electric - F=Eq ∙ gravitational - F=mg
63
What is absolute electric potential calculated using?
V = 1/4πℇ x Q/r
64
What does r equal in V = 1/4πℇ x Q/r?
Distance from the charge Q
65
When will two points in an electric field have an electric potential difference between them?
If they have a different absolute electric potential
66
What is electric potential difference?
The energy required to remove a unit charge between two points in an electric field that have a different electric potential
67
Where are field lines in relation to equipotential lines?
Perpendicular
68
When is electric potential zero?
At infinity

Physics paper 2 (7 decks)

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