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Physics - Topic 7 - Electric and Magnetic Fields > Electric Fields > Flashcards

Electric Fields Flashcards

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1
Q

Define an Electric Field.

A

Is a region in which a charged particle experiences a force

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2
Q

What is Electric Charge measured in?

A

Coulombs

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3
Q

Oppositely charged particles [………] each other.

A

attract

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4
Q

Like charges [……….] each other

A

repel

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5
Q

What can you assume if the charged object is a uniformly charged sphere?

A

All the charge is at the centre, it behaves like a point charge.

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6
Q

How can Electric and Gravitational Fields be represented?

A

By drawing field lines

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7
Q

What does Coulombs Law give us?

A

Gives us the force of attraction or repulsion between two point charges in a vacuum.

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8
Q

What is Coulombs Law?

A

Can also merge the q1 q2 and r*2 to the other side to give one equation

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9
Q

How do you calculate Coulombs Constant?

A
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10
Q

Show the equation for Coulombs Law but with Coulombs Constant instead.

A
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11
Q

What do the symbols stand for in this equation?

A

F = Force of attraction or repulsion between two point charges in a vacuum

ε0= the permittivity of free space (= 8.85 x 10*-12 Fm*-1)

Q1 & Q2 = Are the charges

r = the distance between Q1 and Q2

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12
Q

What is Epsilon naught?

A

ε0= the permittivity of free space

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13
Q

What is the value for Epsilon Naught?

A

8.85 x 10*-12 Fm*-1

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14
Q

What is Epsilon Naught measured in?

A

Farads per metre (Fm*-1)

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15
Q

What will F be if the charges are opposite? Including Coulombs Law values.

A

The Force is attractive

  • In Coulombs Law F will be NEGATIVE
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16
Q

What will F be if the charges are alike? Including Coulombs Law values.

A
  • The Force is REPULSIVE
  • F will be POSITIVE
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17
Q

Coulombs Law is an […………]

A

Inverse Square Law

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18
Q

Why is Coulombs Law an Inverse Square Law?

A

The further apart the charges, the weaker the force between them.

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19
Q

What happens if the point charges are between air? Coulombs Law.

A

Air can be treated as a vacuum so you can use the Epsilon Naught constant

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20
Q

In Coulombs Law, what do you do if the point charges are not in a vacuum?

A

Epsilon Naught is replaced by the permittivity value.

21
Q

How do you use an electric balance to measure the force between two charges?

A

1 - Fix a charged sphere to a mass balance and zero the balance

2 - Clamp another charged sphere carrying the same charge directly above the first sphere

3 - The spheres will repel each other, causing the lower sphere to push down the scales, so the scales will register a mass

4 - Use W = mg to calculate the force

5 - If you vary the distance, r, you found that F is proportional to 1/r*2

22
Q

What is the definition of Electric Field Strength?

A

Force per unit Charge

23
Q

What is the Electric Field Strength Equation?

A

E = F/Q

E = Electric Field Strength (NC*-1 newtons per coulomb)

F = Force (N)

Q = Charge (C)

24
Q

A Radial Field is…

A

Inversely Proportional to r*2

25
Q

How can you identify if a object has a Radial Field?

A

If it has a point charge

OR

or any body that behaves as if all its charge is concentrated at the centre.

26
Q

Is an Electric Field a Scalar or a Vector?

A

Vector

27
Q

In what direction does an Electric Field flow?

A

Points in the direction that a positive charge would move

28
Q

What kind of field must it be if it has the same Electric Field Strength throughout?

A

Uniform field

29
Q

In a Radial Field, what does the Electric Field Strength depend on?

A

Depends on the distance r from the point charge Q

30
Q

What is the Electric Field Strength equation including Coulomb’s Constant? k

A

E = kQ/r2

E = Electric Field Strength (NC*-1)

k = Coulomb’s Constant

Q = Point charge (C)

r = distance from the point charge (m)

31
Q

What is the value of Coulomb’s Constant (k)?

A

8.99 x 109 N m2/C2

32
Q

What is the Electric Field Equation without Coulomb’s Constant?

A

E = Electric Field Strength (NC*-1)

e0 = Epsilon Naught (8.85 × 10^-12 Fm*-1)

Q = Point charge (C)

r = distance from the point charge (m)

33
Q

What is the graph for E = 1/r*2 ?

A

Shows that the field strength decreases as you get further away from Q.

34
Q

In a Uniform Field what is the same everywhere?

A

Electric Field Strength

35
Q

How can you produce a Uniform Field?

A

By connecting two parallel plates to the opposite poles of a battery.

  • One plate should be positive and the other should be negative
36
Q

What are the field lines like in a Uniform Field?

A

The field lines are parallel so they’re always the same distance apart.

This means the field strength is the same at all points within the field.

37
Q

What does the field strength between two parallel plates depend upon?

A

Depends upon…

  • The Potential Difference, between the plates, V.
  • Distance, d, between them.
38
Q

Define Electric Potential

A

Potential energy that a unit positive charge ( + 1C) would have at that point

39
Q

What does the Electric Potential depend upon?

A

Depends on…

  • HOW FAR it is from the CHARGE creating the Electric field.
  • Size of the CHARGE
40
Q

What is the Electric Potential Equation, in a Radial Field?

A

V = Electric Potential (V)

Q = Size of the charge (Q)

r = distance from the charge (m)

41
Q

What does the sign of V depend on?

A

Depends on Q

E.G - V is POSITIVE when Q is POSITIVE, therefore the force is repulsive.

V is NEGATIVE when Q is NEGATIVE, therefore the Forces ATTRACT.

42
Q

When is an Electric Potential at its greatest possible value? What happens as V gets further away from this point?

A

V is greatest directly next to the charge, V decreases as the distance from the charge increases.

43
Q

Show the V over r graph for a Repulsive force and describe what you see.

A

You see that…

  • V is initially positive and gets closer to zero as r increases
44
Q

Show the V over r graph for an Attractive force and describe what you see.

A

You should see…

  • V is initially negative and gets closer to 0 as r increases.
45
Q

What does the gradient of a V over r graph give us?

A

Gives the Field Strength at that point.

E = (delta) V / (delta) r

46
Q

How can you use a E over r graph to find the change in Electric Potential (change in V)?

A

Take the area underneath two points on the graph of E against r

47
Q

What do Equipotentials show?

A

Show all points of Equal Potential in a Field

48
Q

What is different about equipotentials for Radial Fields & Parallel Plates?

A
  • Equipotentials in a Radial Field are the same distance from the centre of the charge, spheres.
  • For Parallel Plates the Equipotentials are flat planes.
49
Q

What happens to the Energy Transferred to a charge travelling along an Equipotential?

A

No work is done! Because you are travelling ALONG it!

Physics - Topic 7 - Electric and Magnetic Fields (4 decks)

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