Chapter 17 Flashcards
Electric force
interaction between 2 charged objects (N)
Electric field
Force exerted on a tiny + test charge (q) placed at that point DIVIDED by magnitude of test charge
Units: (N/C)
Equation for E-field
charge (q) creating the field
(E-field with respect to location)
Equation for E-field
charge (q) experiencing field
(E-field with respect to location)
Work
force acts on an object and causes a displacement
Energy
conserved substance like quantity (can be stored in multiple modes but its always the same thing)
Energy storage modes
gravitational, kinetic, elastic, electrical
Equation for WORK
Is work stored in a system?
no
Is energy stored in a system?
Yes
What conditions of force and displacement cause no work?
No work is done when: force PERPENDICULAR to displacement
Electric potential energy
amount of energy needed to move a charge against an E-field
Units: J
Does electric potential energy depend on the path taken when moving from A to B?
No, PE is independent of path taken
Electric potential difference
diff in potential energy/unit charge between two locations in an E-field
units: V (J/C)
What does electric potential difference depend and not depend on?
Does not depend on: test charge (q)
Depends on: charges that create the field
How can electric field be defined in terms of electric potential difference?
E-field: the rate that electric potential decreases over distance in that direction
Equipotential line
- Line along which the electric potential is constant
- Isolines PERPENDICULAR to E-field at all points
- Continuous (never end)
Equipotential surface
Surface all at the SAME potential
Example: conductor in static equilib
Equation for electric potential energy (PE)
PE = q∆V
Equation for electric potential difference (V)
V = W/q
V = Ed
Equation for kinetic energy (Ek)
Ek = ½ mv2
Equation for gravity force and
Fg = m g
g = 10N/kg
Equation for Gravitational Potential energy
Eg = m g h
g = 10N/kg
What plate has a higher potential negative or positive?
+ plate has higher potential
Where will charged objects naturally move to in an electric field?
+q: move from high → low potential
–q: move from low → high potential
Where will charged objects naturally move to in an electric field?
+q: move from high → low potential
–q: move from low → high potential
Capacitance
ratio of the electric charge on each conductor (Q) to the potential difference (V) between them
A higher capicatance (C) means that a conductor can hold more or less charge at 1V?
higher C = can hold many Coulombs of charge at 1V
Equation for CAPACITANCE
q = CV
Equation: amount of energy stored in a capacitor
Ecap = (½)CV2
What is a CAPACITOR?
device use to store electric charge & consists of 2 conducting objects (plates/sheets)
Equation: CAPACITANCE for a parallel plate capacitor
A = area of either plate
ε0 = 8.85 x 10-12 (C2/Nm2)
What does 1 Fardad (F) =
1 F = 1C/V
Equation: electric potential (V) of a single point charge
The potential around + charges is always +/–? What about around – charges?
Potential around + charges = +
potential around – charges = –
How can you add voltages?
Voltages add arithmetically (superpositon)
VA = VAB + VAC …
Can voltages be negative?
Yes! Because we choose an arbitrary 0
What is the coulomb’s constant: k =
k = 9 x 109 (Nm2/C2)
Charge of one electron/proton
1.6 x 10-19 (C)
Mass of 1 proton
k = 1.67 x 10-27 kg
Mass of 1 electron
9.11 x 10-31 kg
Unit conversions
1 N =
Unit conversions
1 J =
Unit conversions
1 V =
Unit conversions
How to go from N/C to V/m?
1 electron volt (eV) =
1 eV = 1.6 x 10-19 J
