Electrostatics III Pt I

  1. Electric force has an associated form of _______ energy, similar to gravitational force and spring force. If an object moves "with nature," then potential energy ________
    • potential energy
    • decreases
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  2. Define Work 
    A positive charge q is repelled by a stationary _______ source charges. A hand must push on the charge +q in order to move it closer to the _______ source charges.
    The hand does work, transferring energy into the system of charges, ________ the system's energy (_____ _____ energy)
    • Work the transfer of energy to or from a system by external forces that act on it as it undergoes displacement
    • positive
    • positive
    • increasing
    • electric potential energy Ue
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    • B. potential energy depends on position.
    • For part 1, they are equidistant from the charge, so no change or high to high (0). For 2, we go from high to low, so -. For 3. We go from low to high, so +, and for 4, we go from high to low, so -
  4. Let's take a charge q = 10 nC and set Uelec = 0 at a point A. How do we find the potential energy at some other point B or C?
    • We must measure the amount of work it takes to move the charge from point A to that other point
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  5. It takes the hand 4 μJ of work to move the charge q from point A to point B, thus, its electric potential energy at B is (Uelect)B = _____. Similarly, (Uelect)C = ____. Since Point C is closer to the sources than point B, the potential energy at point C should be ______ than at point B.

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    • 4 μJ
    • 6 μJ
    • higher
  6. According to Coulomb's law, the electric force is proportional to the ______. Thus, a larger charge would require the hand to do _____ work.
    In turn, the work is also proportional to the ______:
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    A charged particle's potential energy is _______ _______ to its charge
    • charge
    • more
    • charge
    • directly proportional
  7. State the expression for the electric potential energy that any charge q would have if placed at some point B given the following ratios of electric potential to electric charges. Also state which part is associated with point B and which part depends on the charge we place at B
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    • Potential energy = (electric potential)(charge) or (Uelec) = Vq
  8. Define Electric Potential (V) and state the equation
    There is a relationship between electric potential and electric potential energy. The ______ ______ tells us how a source will exert a force on q; the electric potential tells us how the source charges would provide q with ______ ______.
    The unit of potential energy is the ______ ____ _____ or the _____
    • The electric potential V: the potential for creating an electric potential energy if a charge is placed at a given point 
    • Uelec = qV
    • electric field 
    • potential energy
    • joule per coulomb, or volt V: 
    • 1 V = 1 J/C
  9. In the electric field model, source charges alter the _____ around them, creating an ______ _______ field and a _____ field.
    • space 
    • electric vector field 
    • scalar field
  10. The scalar field is called the _______ _______

    Define equi potential surfaces and explain how they would work in the diagram below
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    • electric potential
    • Equi potential surface: any point on this surface will have the same potential value
    • So here, from any 3 position to another 3 position, no energy is spent. However, from an 8 to 3 or vice versa, energy must be spent
  11. For both Electric field vector and Electric Potential, state:
    The formulas
    What each tells us about source charges
    Type of Quantity (vector or scalar)
    The potential has a value at _____ _____ in an electric field
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  12. For each statement below specify whether it speaks of electric potential (V) or potential energy (Ue)
    Charge-field system: Due to an interaction between the field and a charged particle placed in the field 
    Created by the source charges
    Present whether or not a charged particle is there to experience it.
    Interaction energy of a charged particle with the source charges 
    Field Characteristic: Independent of the charge 
    Charge-field system: Due to an interaction between the field and a charged particle placed in the field 
    Field characteristic: The difference in potential (ΔV) is proportional to the difference in potential energy (ΔUe)
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    C.  It is independent of the charges +q and -q. Hence, it will be same for both.
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    D. It must go to a lower potential, they didnt tell us the direction of the E field so we can't tell whether it goes to a strong electric field or a weaker electric field, we can't say A or B and E. is eliminated
  15. The force on charge q is zero. No _____ is needed to move it from A to B. Charge q's electric potential energy remains _________ as it is moved from A to B:
    (Ue)B = _____ → VB = ____
    The potential difference (state the formula) is ______
    • work
    • uncharged
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  16. How is a potential difference created? The hand must do work on ___ to push it from A to B. There must be an electric potential difference ΔV between A and B. 
    The capacitor still has no _____ _____ but charge has been ______ to give the plates charges +Q and -Q
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    • A potential difference is created by separating positive charge from negative charge.
    • +q
    • net charge
    • separated
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    B. with the plates, the E field is uniform, the positive charge will try to get the negative plate so the potential energy would be zero at the negative. It would take more energy to displace the hypothetical charge over to the positive end, hence electric potential increases and we go from negative toward positive

    Keep in mind that potential energy will be related to work done
  18. When you shuffle your feet across the carpet, you pick up charge from the floor. There is a ______ ______ between your body and, say, a nearby doorknob. The potential difference can be _______ or more, enough to create a spark as the excess charge moves from _______ to _______ potential
    • potential difference
    • 10,000V
    • higher to lower potential
  19. Lightning is the result of large ______ ______ built up by ______ _______ within clouds due to collision between small ice particles 
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    • potential differences 
    • charge separation
  20. A common and important means of creating a fixed potential difference is the _______. Potential difference between two point is often called the _______. The potential difference between a battery's terminals as the ________ "across" the battery
    • battery
    • voltage
    • voltage
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  21. The nerve and muscle cells, active processes create a potential difference across the _____ _______ of about 70 mV. The membrane potential is caused by an imbalance of _______  (___) and _______ (___) ions. A ______-_______ exchange pump continuously pumps Na+ out of the cell and K+ into the cell. During one pumping cycle, there is a net transfer of one positive charge out of the cell causing a _______ _______
    • cell membrane
    • potassium (K+) and sodium (Na+) ions 
    • sodium-potassium exchange pump 
    • charge separation
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  22. The potential at a given point depends on where we choose V to be _____, but the difference is _______ of any choices. The voltmeter is a instrument for measuring _______ _______, and always has two inputs
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    • zero
    • independent
    • potential difference
  23. How can 120V of a household electric outlet produce a shock that is definitely painful and possibly fatal when the potential difference of 10,000 V when you scuff your feet on the carpet is not? (3-story)
    It is the quantity of charge transferred that determines the physiological effect of a shock. 

    The potential difference produced when you scuff your feet on the carpet is large, but the total amount of charge transferred when you touch a doorknob is quite small.

    The voltage of electric outlets is much smaller, but the charge transferred can be much greater.
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    B. The charge difference will be the same potential, there should be an equi potential between those two positions. Point 1 is 3 (set to the max because of the +) and Point 2 is zero, because it comes from the negative (which we automatically set to the minimum: zero). So the difference between those two poles will be 3.
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    • Because they are different sizes, they can't have the same charge. They also can't have the same electric field:
    • Electric field = Kq/r2 = potential/r
    • The two metal spheres are connected by a metal wire (great conductor), so they will have the same potential, A.
  26. Energy is conserved in an isolated charged system. State the formula for: 
    W (2)
    ΔK (4)
    Positive particle speeds up (___ > ___) → ____ > ____, i.e. it moves from ______ to ______ potential and vice versa. This situation is reversed for a ______ charge. A negative charge speeds up if it moves into a region of ______ potential
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    • (Kf > Ki) → Vi > Vf
    • higher to lower potential 
    • negative charge
    • higher potential
  27. The dashed green lines are lines of constant ______ ______. The potential is 500 V at ______ points on this line. A double-headed green arrow is used to represent the ______ ______ 
    A positive charge speeds up (ΔK __ 0) as it moves from ______ to ______ potential (ΔV ___ 0). ______ _____ energy is transformed into ______ energy. 
    A positive charge slows down (ΔK ___ 0) as it moves from ______ to ______ potential (ΔV ___ 0). ______ energy is transformed into ______ ______ energy
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    • electric potential
    • all points
    • potential difference
    • ΔK > 0
    • higher to lower potential (ΔV < 0)
    • Electric potential energy
    • kinetic energy
    • ΔK < 0
    • lower to higher potential (ΔV > 0)
    • Kinetic energy
    • electric potential energy
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  28. Problem Solving Strategy Conservation of energy in charge interactions 
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  29. Electric energy can be transformed into other types of energy in addition to kinetic energy. When a battery is connected to a light bulb, their electric potential energy is transformed into _______ ______ (__), making the bulb hot enough to glow brightly. State the formula for this energy transformation
    • thermal energy (Eth)
    • ΔEth = -qΔV
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    E. The direction of electric field in the given figure is directed downwards because electric from positive potential to negative potential. Thus, the potential energy of the proton decreases in downward direction, and kinetic energy increases in downward direction. Therefore, proton moves downward with increasing speed.
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  32. Another unit of energy that is commonly used in atomic and nuclear physics is the electron-volt.
    Define One electron-volt and state the value/conversion to CV and J 
    You must convert this energy to ____ before doing most calculations
    • One electron-volt: the energy a charge-field system gains or loses when a charge of magnitude e is moved through a potential difference of 1 volt
    • 1 eV = 1.60*10-19 C⋅V = 1.60*10-19 J
    • Joules (J)
Card Set
Electrostatics III Pt I
Electrostatics III Pt I