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A Physics Finale pt 2. > Unit 4.1 Capacitance > Flashcards

Unit 4.1 Capacitance Flashcards

1
Q

What is a capacitor?
(3-way)

A
  • An electric device designed to
  • store electrical charge
  • and hence electrical energy
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2
Q

What does a capacitor consist of?
(4-way)

A
  • 2 conducting metal plates
  • parallel to each other
  • separated by an insulating material:
  • “dielectric”
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3
Q

List 5 different uses of capacitors in a circuit?
(Pick and match type sh)

A
  • Local energy storage
  • Voltage spike suppression
  • Timing circuits
  • Signal filtering
  • Nuclear fusion research (high energy laser)
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4
Q

How do u draw how a capacitor works?
(Get whiteboard)
(Booklet sorry)

A

Once again….

  • 2 cells
  • the capacitor
  • electrons
  • Positive and negative sides
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5
Q

Explain how a capacitor becomes charged when a battery is placed across it? PT. 1
(4-way)

A
  • Electrons from capacitor attracted to positive terminal of the battery
  • Leaves a positively charged plate on capacitor,
  • attracts electrons from negative terminal of the battery
  • Electrons stored on capacitor plate
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6
Q

Explain how a capacitor becomes charged when a battery is placed across it? PT. 2
(3-way)

A
  • One plate = positively charged, other = negatively charged
  • Charge = equal
  • Once voltage across capacitor = battery, charging stops
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7
Q

What is charge (Q) measured in?

A

Coulombs
(C)

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8
Q

Do u know the circuit symbol for a capacitor?

A

Imagine paying to add pictures.

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9
Q

Define capacitance
(2-way)

A
  • The charge per unit potential difference
  • across the 2 plates
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10
Q

What is the formula for a capacitor?
(In data booklet)

A

C = Q/V

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11
Q

Formula for a capacitor expressed in words?

A

Capacitance = charge on either plate/pd between plates

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12
Q

Define C
(Capacitor formula)

A

Capacitance
(F aka Farad)

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13
Q

Define Q
(Capacitor formula)

A

Charge
(C)

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14
Q

Define V
(Capacitor formula)

A

Voltage
(V)

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15
Q

1 Farad = ?

A

1 coulomb per volt

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16
Q

1F = ?

A

1CV-1

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17
Q

How would u calculate t on a charged plate?

A

Q = It

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18
Q

How would u find the charge stored on each conducting plate of the capacitor
(3-way)

A
  • Q = CV
  • They’re only positive & negative sides
  • therefore same answers but…
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19
Q

Which capacitor will have greater capacitance in terms of distance between plates?
How come?
(3 things)

A
  • Smaller distance
  • Stronger field between plates
  • Stronger interaction between the charges
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20
Q

Distance and Capacitance relationship?

A

They are inversely proportional
(C ∝ 1/d)

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21
Q

Which capacitor will have greater capacitance in terms of area of plates?
How come?
(1 + 2-way)

A
  • Bigger area
  • More capacity
  • … to store electric charge
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22
Q

Area and Capacitance relationship?

A

They are directly proportional
(C ∝ A)

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23
Q

What’s the equation for capacitance?
(In data booklet)

A

C = ε0A/d

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24
Q

Define C
(Capacitance equation)

A

Capacitance
(F)

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25
Q

Define A
(Capacitance equation)

A

Area of plates
(m2)

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26
Q

Define d
(Capacitance equation)

A

Distance between plates
(m)

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27
Q

Define ε0
(Capacitance equation)
(A constant)

A

Permittivity of free space
(8.85 x 10-12 Fm-1)

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28
Q

What is a dielectric?
(2-(1thing)-way)

A
  • A material used in-between the 2 plates
  • within capacitor
  • That has effects on the value capacitance
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29
Q

How does a dielectric effect the value capacitance?
(4 things)

A
  • Has dipolar effects inside
  • If polarised, increases capacitance
  • Unpolarised = no effect
  • Polarises due to pd across it
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30
Q

How is a uniform electric field obtained with a capacitor in a circuit?
(3 things)

A
  • Between the 2 parallel metal plates w/
  • distance apart (d)
  • & has a pd (v)
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31
Q

Describe field lines
(3 things + () <- literally)

A
  • Parallel to each other
  • At right angles to the plate
  • Directed from positive to negative plate
  • (Direction a positive test charge would move)
32
Q

How do u increase the electric field strength (E)?
(2 ways)

A
  • Increase the pd (V)
  • Decrease plate separation (d)
33
Q

Electric field strength equation?
(In data booklet)

A

E = v/d

34
Q

Define E
(Electric field strength equation)

A

Electric field strength….
(Nc-1)

35
Q

Define v
(Electric field strength equation)

A

Voltage, potential difference
(V or Jc-1)

36
Q

Define d
(Electric field strength equation)

A

Plate separation
(m)

37
Q

Tip for finding out the electric field strength?
(2-way)

A
  • As separation always very small…
  • E will always be the bigger answer
38
Q

How is energy being stored in a capacitor?
(3 things)

A
  • When charging the capacitor,
  • work is being done
  • assembling the charge on each plate
39
Q

How is the energy stored in a capacitor equation formed?
(4 steps)

A
  1. Voltage against charge
  2. Straight line
  3. Area under = energy stored
  4. J = ½ QV
40
Q

Therefore, energy stored in capacitor equation?
(in data booklet)

A

J = ½ QV

41
Q

What are the 2 alternate formulae to use to find energy stored in capacitor?

A
  1. J = ½ CV2
  2. J = ½ Q2/C
42
Q

(Simple)
How do u find total capacitance in series?

A
  • Same to finding resistance in parallel
  • 1/ CT = 1/C1 + 1/C2 + 1/C3
43
Q

(Simple)
How do u find total capacitance in parallel?

A
  • Same to finding resistance in series
  • CT = C1 + C2 + C3
44
Q

What’s another way of saying the total capacitance?

A

The effective capacitance

45
Q

How to find voltage in capacitor in series?
(Use data booklet)

A

Charge/Capacitance = Voltage

46
Q

How to find voltage in capacitor in parallel?
(Use data booklet)

A

Charge/Total capacitance = Voltage

47
Q

How to find charge in capacitors in series?
(3 steps)

A
  1. Find total capacitance
  2. Q = VC
  3. Charge = same
48
Q

How to find charge in capacitors in parallel?
(We partly don’t know yet but…)

A
  1. Probably use the formula
49
Q

What does it mean for a capacitor to discharge?
(2 things)

A
  • Provide electrons for the circuit
  • Like a battery
50
Q

What 3 factors determine how long it takes a capacitor to fully discharge?

A
  • Capacitance (C)
  • Voltage (V)
  • Resistance (R)
51
Q

How is C and V a factor of how long a capacitor takes to discharge?
(2-way)

A
  • Determines how much charge,
  • is stored Qo
52
Q

How is R a factor of how long a capacitor takes to discharge?
(2-way)

A
  • Determines the size of current
  • that flows to discharge the capacitor
53
Q

What type of decrease would the graph show on how the charge on the plates changes with time?

A

Exponential decay

54
Q

How would u define exponential decay for the graph showing “charge on the plates changes with time”?
(2-time)

A
  • The percentage decrease,
  • is constant per unit time
55
Q

What’s the general formula for exponential decay?
(In data booklet)

A

A = Aoe-λx

56
Q

What effects the rate of decrease of the exponential decay formula?
(2-wayway)

A
  • Decay constant
  • aka λ
57
Q

What are the 3 measurements that can be subbed in exponential decreases for capacitor discharge?

A
  • Charge
  • Current
  • Voltage
58
Q

What’s the exponential decrease formula for Q of capacitor discharge?
(In data booklet)

A

Q = Qoe-t/CR

59
Q

How do u find the exponential decrease formula for I and V?
(2 things)

A
  • Just swap the Q
  • Don’t forget -t/CR
60
Q

Formula for time constant (CR)?
(In data booklet)

A

Q = Qoe-t/CR

61
Q

Define Q
(Time constant formula)

A

Charge at any time t
(C aka coulombs)

62
Q

Define Qo
(Time constant formula)

A

Initial charge
(C aka coulombs)

63
Q

Define t
(Time constant formula)

A

Any time after discharging has begun
(s aka seconds)

64
Q

Define C
(Time constant formula)

A

Capacitance of capacitor
(F aka farads)

65
Q

Define R
(Time constant formula)

A

Resistance of load
(Ohms)

66
Q

What’s the difference if CR is small?
(2 features)

A
  • Q quickly decays
  • Steeper curve on graph
67
Q

What’s the difference if CR is large?
(2 features)

A
  • Q slowly decays
  • Less steep curve on graph
68
Q

How to show CR (time constant) must have units of seconds?
(4 by 4 steps)

A
  1. FxR
  2. C = Q/V & R = V/I
  3. It/v x V/I
  4. = t
69
Q

Definition of time constant?
(3-way although cut 1 way…)

A
  • Time constant, for a discharging capacitor,
  • is time taken for charge/current/voltage
  • to decrease to 37% of og val.
70
Q

How do u find the “time constant” from the CR formula?
(Wow… <- clue right there)

A
  1. Take logs.
  2. Use the whiteboard
  3. That one chemistry lesson
71
Q

What are the 2 ways to obtain a value for the capacitance of the capacitor with graphs?

A
  • t = RC for normal graph @ 37% (y axis)
  • In v graph and do y = mx + c
72
Q

The clarification is lost D: ^^

A

Lesson learned?

73
Q

What’s an opposite for a capacitor discharging?

A

…. the capacitor charging

74
Q

What’s the difference for capacitor charging?
(3 things)

A
  • Only charge & voltage increases
  • No current + no decrease
  • Different formula
75
Q

Equation for capacitor charging?
(Not in data booklet)

A

Q = Qo(1 - e-t/CR))

76
Q

How can u tell on the graph that it’s capacitor charging?

A

The opposite of capacitor discharging:
- Goes up insteada down

77
Q

Probably not the best….. once again…. however.

A

I’d probably spam ppq, surely it can make things more clarifying?

A Physics Finale pt 2. (7 decks)

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