Unit 4.2 Electrostatic Fields Flashcards by Shirou Aizen

What does electrostatically charging an object involve?

Redistribution, addition or removal of electrons

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What are the 2 ways to charge and object?

Charging by friction
Charging by induction

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What is charging by friction?
(4-way)

Process of friction generates energy
… to remove some electrons from the surface
… of the material and place them
… onto the duster

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What is charging by induction?
(2-way + 2-way)

Electrons redistribute themselves on the leaves
… of the electroscope
Positive charge induced on the
… top plate of the electroscope

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Examples of everyday charging?
(Just know that one)

Lightning clouds
Hair n stuff
Christmas jumper
Comb??

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What is the 2 principles of electrostatics?

Like charges repel
Unlike charges attract

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Show me like charges repel?
(2 light things)

Positive to a positive repel
Negative to a negative repel

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Show me unlike charges attract?

Positive to a negative attract each other

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Define induction in general?

When it’s not touching

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Define conduction in general?

When it’s touching

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Explain gold-leaf electroscope

Later

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Explain electric field lines for a positive point charge?

Arrows directed away from center

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Explain electric field lines for a negative point charge?

Arrows directed towards the center

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What would u see for electric field lines if there’s a positive point charge near a negative point charge?
(2-way + 3-way)

Arrows from positive point charge
directed towards negative point charge
The direction of the arrows some are straight
Others are curved
Based on closeness

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How would u increase electric field lines curve strength?
(2 things)

Decrease distance
Increase quantity of point charges

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Diagram of field between 2 parallel plates?

Whiteboard if u need it

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Explain electric field between 2 oppositely charged parallel plates?
(1 + 2-way + 1 thing)

Field lines = straight & parallel to one another
∴ field’s strength uniform throughout
… except edges
At edges = field strength slightly less

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What happens to the field if u increase the quantity?
(2 comparisons)

Magnitude doubles if u add 1 (+2Q)
Magnitude triples if u add 2 (+3Q)

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What would happen to the field for ‘unlike point charge’
(Field between two point charges)
(2 things)

Attraction
Basically looks like magnet directions/arrows
(u should probably draw it)

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What would happen to the field for ‘like point charge’
(Field between two point charges)
(2 things + 2-way)

Repel
Similarities for less curves
Likewise to negative version
…. but arrows towards negative

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What’s the jig with field for ‘like point charge’?
(1 thing + 3-way)

It has a point where the field is zero
Due to vector lines at these points…
are equal and in opposite direction
∴ they cancel out

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Diagram for the field ‘like point charge’
(Field between two point charges)

Whiteboard

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What does the density of field lines indicate?

Its relative strength of the field

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What does the direction of the field line indicate?
(3-way)

Direction of the force
experienced by a small positive charge
placed in that position

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How do u calculate the strength of a charges' (Q) field (E)? (2-way + 1 way?)

- Place a positive test charge q - in the field - Measure force acting on it

Electric field strength equation? (Analogous to capacitance version O_o) (NOT IN DATA BOOKLET)

E = f/q

Define E (Electric field strength equation)

... The electric field strength (NC^-1)

Define f (Electric field strength equation)

Force (N ig?)

Define q (Electric field strength equation)

Charge (C)

Electric field strength equation expressed in words?

Electric field strength = Force/Charge

Definition of the electrical field strength?

Force per unit charge

The 2 different units for E (electrical field strength)?

- NC^-1 - Vm^-1 (E = v/d, capacitance version)

The 2 things to note for electrical field strength equation + positive test charge? (Lil check up)

- Magnitude of the field strength at any point in the field is independent of the test charge - The direction of the field depends upon the charge of Q which generates the field; however, a positive test charge must always be sued to define the direction

What equation for E in a radial field? (In data booklet)

E = (1/4πε₀) x Q/r²

Define 1/4πε₀ (E in a radial field equation)

= 9 x 10⁹ Fm^-1 A constant.... kind of.

What's the jig with 1/4πε₀?

k = 1/4πε₀ = 9 x 10¹⁰

Define Q (E in a radial field equation)

Charge (C)

Define r (E in a radial field equation)

Radial distance from point charge (m)

What's the ε₀ known as?

Permittivity of free space

For E in a radial field, what is the relationship between charge and E?

They're directly proportional (E ∝ Q)

For E in a radial field, what is the relation between distances and E?

They're inversely proportional (E ∝ 1/r²)

What's the relationship between E and radial distance another example of?

The inverse square law

If r doubles, what happens to E? (Relationship between E and r)

E becomes 1/4 of its previous strength

If r is halved, what happened to E? (Relationship between E and r)

E becomes 4 times greater

Combining electric fields using vector addition (lil check up)

I'll come back to it. It's actually a bit similar to basic physics vectors. Tho obviously, "analogous"

Tell me what u know so far for the combining electric fields (Future self)

- Once again, like resolving vectors - Tho apparently mostly u wouldn't be needed sin + cos - (Horizontal & vertical components) - Typical equation is E = k x Q/r² - k obviously the constant - Take in consideration of what happens between + against - - or - against - or + against + - Don't forget to square - In addition, finding magnitude and direction - I'll stick with this

What's it called for if we consider force experienced by a second charge (q), place in a specific position in some rando's field

Electrical field force (Coulomb's Law)

The typical equation for finding force in an electric field? (Capacitance type shi)

F = E x q

Therefore, the equation for the electric field force? (In data booklet except in k terms)

F = k x (Q₁Q₂)/r²

Define F (Electric field force eqn)

Force between charges (N)

Define Q (Electric field force eqn)

Charge (C)

Define k (Electric field force eqn)

- Constant of proportionality - Coulomb's constant (Nm²C^-2 aka 1/4πε₀)

Define r (Electric field force eqn)

Separation of charges (m)

Define ε₀ (Electric field force eqn)

Permittivity of free space (Constant)

Definition for Coulomb's law? (4-way)

- Force between charges is directly proportional... - to the product of charges - and inversely proportional to - ... the distance between charges **squared**

What to take in consideration for electric field force eqn? (2-(way) + 2 things)

- For finding the charge, be aware whether it's + or - - (Rules of magnets n stuff) - If attracting, Force = negative - If repelling, Force = positive

Glad i did that hw asap

But now how much can I recall? + i forgot what i was gonna say

Once again, now u better be sorry

...

Explanation for the equation for electrical Potential Energy in terms of force/distance graph? (1, 4-way)

- In a Uniform Field, - area under force/distance graph - = work done when moving - charge through a distance (x)

Hence, equation for electrical Potential Energy [in distance]?

△W = F △x

Definition of potential energy? (In terms of charge ig)

- The energy required to move - the charge from infinity to - a point in a field

However, what about electrical Potential Energy in a radial field? (4-way)

- Same principle - Area enclosed under... - force/radius represents work done - when charge moved from r1 to r2 (positions)

What does the force/radius graph look like for electrical potential energy in a radial field?

A curve

In addition, how would u gain the area in the force/radius graph? (Electrical Potential Energy in a radial field)

Count the squares...

Thus, the equation of our line for electrical Potential Energy in a radial field?

F = k x q₁q₂/r² (ofc k = 1/4πε₀

BUT ULTIMATELY, the actual equation for the electrical Potential Energy in a radial field? (In data booklet)

PE = Q₁Q₂/4πε₀r better way for this, k constant.

Explain what it means by infinity? (Electrical Potential Energy in a radial field) (4-way)

- The zero energy reference but as... - Electric Fields, - can be attracting/repelling - either max. or min. PE

What would it mean if the field is attractive? (Electrical Potential Energy in a radial field) (4 things)

- Q₁Q₂ is -'ve - PE = negative - **Maximum** PE at ∞ - Work to move charge in field is **greatest** towards ∞

What would it mean if the field is repulsive? (Electrical Potential Energy in a radial field) (4 things + 1 optional special)

- Q₁Q₂ is +'ve - PE = positive - **Minimum** PE at ∞ - Work to move charge in field is **lowest** to ∞ - Like a spring pushed down...

Explain what the electrical potential (V_E) due to a point charge is? (4-way) (Electrical Potential (V_E of a position)

- The **work done** in... - bringing a **unit positive** charge from - **infinity** to that point - in the field

Equation for Electric Potential _(volt)? (JC^-1) (Electrical Potential (V_E) of a position)

V = W/_Test q

Data booklet edition for equation for Electric Potential _(volt)? (Electrical Potential (V_E) of a position)

W = q △V_E

Derive expression for Electrical Potential V using equation for electrical PE in radial field? (3 by 3 step) (Electrical Potential (V_E) of a position)

- V_E = PE/q - PE = k x Q₁Q₂/r - Hence, V_E = k x Q/r

[Useful] way to imagine potential (work done per unit charge)? (2-way)

- Imagine a "**potential surface**" - created by a point charge

Surface of zero potential would be? (Potential wells and hills)

Flat surface

Explain the positive charge in terms of... (Potential wells and hills) (a thing + 3-way + a things)

- Creates potential "**hill**" - +'ve work done must be done to move - a +'ve test charge closer to it - "as tho u're moving it up a hill" - +'ve work done when **against** electric force

Explain the negative charge in terms off... (Potential wells and hills) (a thing + 3-way + a things)

- Creates a potential "**well**" - -'ve work done to move... - a +'ve test charge closer to it - "as tho u're moving it down a well" - -'ve work done when moving **with** electric force

What's electrical potential (V_E) of a position similar to? (1 imp + 3-way)

- Like PE of a charge in a field - Electrical Potential (V_E) of a point in a field is: - negative in an attractive field - positive in a repulsive field

How to find resultant potential at point x if **multiple charges** is present? (1 thing but optionals if u want)

i.e. Q₁, -Q₂ Q₃ - Algebraic sum of the potentials - Resultant V at X = V₁ - V₂₃

Sketch and label how potential varies with distance for both a positive and negative charge (graph)

Stage is yours

Gradient for [how potential varies with distance (graph)]? (3-way)

- Gradient of graph = rise/run = △V_E/△r - V_E = k x Q/r - ∴ gradient = k x Q/r² = E - but ultimately, gradient = -E

How's that the gradient for [how potential varies with distance (graph)]? (4-way)

- Direction given by charge producing field - Negative charge producing -E (inwards) - Positive charge producing +E (outwards) - ∴, gradient = -E

It's like, I forgot I had physics SO, what's left?:

- Escape velocity in electrical fields (as much as i'd start this first.... it's already a major sell that I didn't do the previous work ¬.¬)

I have a choice: - Make notes for escape velocity in electrical fields - Boycott, start the real revision