Force Types: : Contact & Non-contact Contact: Must touch such as friction or using a rope.Non-contact

Michael Faraday (British: 1791-1867)

Field area around an object that affects other similar objects

Test charge charge that’s in an electric field

Planet

Satellite Proton

Electron

Satellite & electron experience field forces

•Gravitational field by Newton

•Electric field by Faraday

•Non-contact–Remember gravity?2

typ

es o

f Fo

rces

r2

MGF =

ma

•What is the field?

•a (or g)a

r2

MG=

•Non-contact–Remember gravity?–What’s the field for a charge?2

typ

es o

f Fo

rces

F = ma

•What is the field?

•a (or g)

r2

QkF =

qE

•What is the field?

•Ea

r2

MG= E

r2

Qk=

2 ty

pes o

f Fo

rces

F =Eq F = force on test charge

q = charge of test charge

E = Electric Field (N/C)Q creates the

field

Two equations for electric fields

Er2

Qk=

Ele

ctric Field

Lin

es

•Drawing Electric field lines–Rules

•lines tell direction a + test charge will go

•Out of (away from) positiveInto (toward) negative

•Lines always come out the object perpendicular to the surface.

•more lines = stronger field.+ --

+ -

+ +

Sam

ple

Pro

ble

ms

•What is the electric field intensity of a 16 μC particle 5 cm away from the charge?

Er

2

Qk=

E0.05

2

(16x10-

6)(9x109)=

E=5.75x107 N/C

Pro

pertie

s of

cond

ucto

rs in

ele

ctrosta

tic eq

uilib

rium

1. Excess charges gather only on the outside of the surface, never inside.

2. The electric field is zero everywhere inside the conductor.

3. Electric field coming in or out of the conductor is perpendicular to the surface.

------

------

E = 0 N/C

------

--

---- --

--

4. On an irregularly shaped surface, the charge will accumulate more where the radius of curvature is smallest.

This happens because the electrons will repel each other until they reach equilibrium.

Grounding An easy path for e’s to flow to or from

an infinite reservoir of e’s. Usually from the Earth to the electrical object.