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Introductory Physics 2 > Chapter 21 > Flashcards

Chapter 21 Flashcards

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1
Q

What is the Basic Energy Model?

A

Every system in nature has a quantity we call its TOTAL ENERGY (E)
- The total energy (E) is the sum of the energies present in the system

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2
Q

What are the different forms of energy?

A
  1. kinetic energy
  2. gravitational potential energy
  3. elastic potential energy
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3
Q

what is kinetic energy?

A

energy of an object of mass (m) moving with speed (v)

K = 1/2mv^2

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4
Q

what is gravitational potential energy?

A

energy of an object of mass (m) at height (y) (assuming Ug = 0 when the object is at y = 0)
Ug = mgy

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5
Q

what is elastic potential energy?

A

energy of a spring displaced (x) from equilibrium (assuming Us = 0 when the end of the spring is at x = 0)
Us = 1/2kx^2

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6
Q

Energy transformations?

A

Energy can be transformed into energy of another kind within a system

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7
Q

Energy Transferred and work?

A

energy can be transferred between a system and its environment through WORK and HEAT

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8
Q

what is the work-energy equation?

A
  • work is the energy transferred in or out of a system mechanically, by pushing or pulling
  • The total energy of a system changes by the amount of work done on it
  • work can increase or decrease the energy of a system
    ΔE = ΔK + ΔUg + ΔUs + ΔEth + ΔEchem +… = w
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9
Q

what is work?

A
  • work is done on a system by external forces
  • work is scalar
  • SI unit is the Joule; 1 joule = 1J = 1Nm
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10
Q

How are work an electric potential energy related?

A

The electric potential energy of a charge when it is at a particular position is HOW MUCH WORK IT TOOK to move the charge to that position

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11
Q

How are energy and charge related?

A

Think of a mass in free-fall:

  • a positive charge “falls” in the direction of the electric field
  • a negative charge “falls” in the opposite direction of the electric field
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12
Q

When do you do positive work (gain energy/speed)?

A
  • When a positive charge moves against the electric field

- when a negative charge moves in the direction of the

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13
Q

when do you do negative work (lose energy/speed)?

A
  • when a positive charge moves in the direction of the electric field
  • when a negative charge moves against the electric field
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14
Q

What is the potential energy of a system with multiple point charges?

A

For a system of many point charges, the total potential energy is equal to the work that must be done by an external agent to assemble the system from infinity

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15
Q

what is the potential energy for a system with two point charges?

A
  • For a system of two point charges, the total potential energy is

U = Kq1q2/r1*2

  • if q1 and q2 are LIKE charges, POSITIVE work must be done by an external agent to bring the charges together
  • if q1 and q2 are OPPOSITE charges, NEGATIVE work must be done by an external agent to bring the charges together
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16
Q

what is electric potential?

A

Just as the electric field is the force per unit charge, electric potential is the electric potential energy per unit charge:
ΔV = ΔU/q
- Potential is NOT the sane as potential energy
- BOTH potential energy and potential are scalars

17
Q

what is the electron volt?

A

The electron volt (eV) is the energy that an electron gains when accelerated through a potential difference of 1V
1 eV = 1.6x10^-19J

18
Q

What is the electric potential (potential) due to a point charge?

A

The potential created by a point charge (q) at any distance (r) from the charge is
V = Kq/r
- the point charge creates a potential exist everywhere in space around it
- for systems of many point charges, the total potential is just the sum of potentials due to every point charge

19
Q

what are equipotential lines?

A
  • contour lines are lines of constant elevation
  • lines close together indicate steep changes in elevation
  • If we think of previous 3D plots of potential as mountains, and slice them across horizontally, we would get contour lines
  • we call these equipotential lines
20
Q

Equipotential lines have?

A

have physical meaning as well being helpful for visualizing

21
Q

Mechanical energy is conserved in the presence of which of the following types of force?

A
  1. Magnetic
  2. Gravitational
  3. Electrostatic
22
Q

What is the formula that relates Potential Difference (V) to Electric Field (capacitance)?

A 
Q = C*V or E = Q/(Eo*A) or V = E*d
A = area 
Eo = 8.85*10^-12 C^2/N*m^2
23
Q

What are some formulas to solve for capacitance?

A 
C =Q/V or C =Eo*k*A/d or C =Eo*A/d
A = area 
Eo = 8.85*10^-12 C^2/N*m^2
C = Capacitance
V = Potential Difference
k = dielectric Constant
24
Q

What is the formula for Potential Energy that links Capacitance and Potential Difference (Capacitance Potential Energy)?

A

Uc = 1/2CV^2

25
Q

What is the formula for Potential Energy?

A 
P = kqQ/r 
Q = -10*10^-9

Introductory Physics 2 (10 decks)

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