Electric Field - General Physcis - Lecture Slides, Slides of Physics

Download Electric Field - General Physcis - Lecture Slides and more Slides Physics in PDF only on Docsity!

Electric Field

Force at a Distance

Electric charges act on eachother at a distance.

•^

Empty space betweencharges

-^

Net force on a charge

Force has to act on anothercharge.

•^

Specific charge for a specificvalue of force

-^

Value needed for forcemagnitude

^







^





F

F

F

E







(^22) 

 ^



^

kQr

F F^



(^22) 

 ^



^

kQr F F^



Field Strength

The electric field is the electricforce per unit test charge.

•^

Measured in N/C

The field has a value at everypoint in space.

•^

Independent of force value

-^

Parallel to force direction

q





q F^ q

E

 E

^



Point Charge

The field of a point charge is just like the vector force that would act at apoint near the charge.

•^

Magnitude comes from Coulomb’s law

(^2) r kQ

E



Screened Charge

Two oppositely charged pointcharges of 10. nC areseparated by 2.0 mm. Find theelectric field at a point 20.0 mmfrom the midpoint along theline of the charges on thepositive side.

Only the x components matter.

•^

k^

= 8.99 x 10

9

Nm

2 /C

(^2)

•^

q^

= 10 x 10

-^

C

•^

r^

= 20.0 x 10

-^

m

•^

d^

= 1.0 x 10

-^

m

Answer:

E

= 4.5 x 10

4

N/C

1  E

2  E

q^^1

2 q

^

(^2) 

1

d r

kq

E

x

^  

^

(^2) 

2

d r

kq

E

x

^  

Environmental Fields

Electric fields exist fromcharges in the environment.

Distance affects the fieldstrength from point sources.

Typical field strengths in N/C

•^

Radio waves: 0.

-^

Living room: 3

-^

30 cm from a stereo: 90

-^

Fair weather sky: 150

-^

Shower (water on): 800

-^

Thunderstorm: 10,

-^

Cell membrane: 10,000,

next