Electric Fields

Question 1

How electric field patterns are mapped out

Answer 1

Using electric field lines

Question 2

Properties of electric field patterns/field lines

Answer 2

• Never start or stop in empty space, only form charge or at “infinity”
• Never touch/cross
• Have direction
• Density of lines indicates strength of e field
• Parallel and equally spaced lines indicate field of constant field strength

Question 3

Direction

Answer 3

-Tangent to electric field line gives direction which a positive point charge placed at point would move

Question 4

Density

Answer 4

Closely spaced lines indicates greater e field strength

Question 5

Flux

Answer 5

measure of number of field lines passing through an area

Question 6

Electric flux

Answer 6

number of electric field lines penetrating a surface/area

Question 7

Flux formula

Answer 7

Φ = normal component of the field E x area A

Question 8

what is normal

Answer 8

line perpendicular to object/plane

Question 9

Guess’ Law

Answer 9

Electric flux through any closed surface is proportional to enclosed electric charge

Question 10

Guess’s Law Formula

Answer 10

Φ = qₑₙ𝒸/ε₀

Question 11

E

Answer 11

• vector
• points in direction of net electric force on positive charge
• units are N/C

Question 12

F

Answer 12

-vector force on test charge

Question 13

q

Answer 13

• test charge

- scalar

Question 14

E and F

Answer 14

-only parallel if test charge is positive

Question 15

Application of electric fields

Answer 15

Electrostatic dust particle scrubber

Question 16

Electrostatic dust particle scrubber

Answer 16

• particulate collection device
• removes particles from flowing gas
• using force of induced electrostatic charge

Question 17

Common way to produce uniform E field

Answer 17

w/ a parallel plate capacitor

Question 18

Parallel plate capacitor

Answer 18

• Two flat, metal, parallel plates
• One charged neg, one pos
• except for some fringing on edges, field is nearly uniform inside
• everywhere inside capacitor has about same magnitude + direction

Question 19

work done by fields eg

Answer 19

• To lift a positive charge q in a downward field E, requires a force qE
• Positive work done in lifting charge, field does negative work

Question 20

work done on charge

Answer 20

-can go into kinetic e, waste heat, or potential e.
-If there is no friction + acceleration, work goes into change of potential energy:
ΔU = qEΔx

Question 21

Change in potential energy for charge in uniform electric field

Answer 21

ΔU = qEΔx

-sign of Δx determined sign of ΔU

Question 22

work done by field and change in potential energy

Answer 22

-Work done by field is opposite of change n potential energyL

W𝒻ᵢₑₗ𝒹 = -ΔU

Question 23

Electric potential

Answer 23

V, is defined to be electric potential energy per unit charge

Question 24

Electric potential notes

Answer 24

• Constant at any given distance from charged surface in uniform field
• Independent of charge

Question 25

Electric potential formula

Answer 25

V = Ed = U/q

where d is the distance from the charged surface and U is the potential energy

Question 26

SI units for potential

Answer 26

the volt (V)

Question 27

1 Volt =

Answer 27

1 J/C

Question 28

Moving in an electric field

Answer 28

• Electric fields are conservative fields
• when charge moves about, any ΔU is independent of path

-ΔV is independent of path

Question 29

ΔV is independent of path

Answer 29

-If charge takes straight line path from A to B, the change in potential is the same as if it took a long, curvy path to B.

They gain the same amount of J of potential energy