Electrostatics
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ไฟฟ้าสถิต Electrostatics. รายวิชา ฟิสิกส์ 14 รหัสวิชา ว 30214. ครูเทวัญ ดีจรัส. ความเป็นมาของไฟฟ้าและแม่เหล็ก. ค.ศ. 1600 : William Gilbert พบอำนาจทางไฟฟ้าของประจุในแท่งอำพัน ( amber ). ค.ศ. 1785 : Charles Coulomb เสนอกฎของคูลอมบ์.

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ไฟฟ้าสถิต Electrostatics

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Electrostatics

14

30214


  • .. 1600 : William Gilbert (amber)

  • .. 1785 : Charles Coulomb

  • .. 1819 : Hans Oersted

  • .. 1831 : Michael Faraday Joseph Henry

  • .. 1873 : James Clerk Maxwell


Benjamin Franklin



(Electric Charges)

  • 2

  • (C): 1 C 6.24x1018 1 A 1 s



(Conservation of Charge)

  • :

Q = Ne

  • N

  • e = 1.6 x 10-19 C

  • e = -e

  • e = +e


(electrical and conductor)



(Electrostatic Discharge)


Electrical Induction



(Electroscope)




(Coulomb's law)

(Charles Augustin de Coulomb) ( .. 2279)


  • (point charge) :

  • ke

  • ke = 8.9875 x 109 N.m2/C2 =

  • = 8.8542 x 10-12 C2 / N.m2


  • 3


  • (principle of superpositon)

  • 6 1


1

+5.0 C -3.0 C


2

5.3x10-11m


3

4 A, B, C D 4 cm -2 C, 8 C, +4 C 12 C C

A

D

B

C


4

q3 q1 q2 q1=q3=5.0 C, q2= 2.0 C a = 0.1 m


5

0.1 1 60


(Electric field)

Faraday (source charge ) (test charge)


(Electric field)

(E) (Q) (F) q0

F


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-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-


(electric filed lines)

A B



(electric filed lines)


(electric filed lines)


(electric filed lines)

  • 2


Q +Q +q +Q r F +q

q

+Q

+q

r

F


1

A +5 x=0 B -10 x = 10 cm x=-5 cm

A

B


2

P

q1=7.0 q2= -5.0 0.3 x P




A +4 B +16 30cm B

3


4

A +8 B 30 A 20 B


r

r


(Uniform field)




a

q

+

Fe

mg


5

104 0.02 2 2


6

2 15 cm 3000 N/C P

1) A

2) A

3) A


7

0.40 kg = 37 g 10 m/s2


R


Q =

r =


r


10 cm 20

1) 5 cm

2)

3) 12 cm

8


  • :

  • N-m2/C


(1) :

(2) :

(3) :

  • (net flux)


()

  • E

  • (Gaussian surface)


()

  • qin E


  • (surface integral)


9

q


10


11


(Energy potential)

(Ep)

q q q q q

A


+q

A B

+q A B

+q B


q Q B A


B

A


B

A


Q1, Q2 Q3 R1, R2 R3

Q1 Q2


Q3 Q3 Q1 Q2


(Electric potential)

V = /

EP =

q =

N Q1, Q2, Q3, , QN r1, r2, r3, , rN



12

4x107 m/s 900 N/C


13

10 C 50 V/m 1


14

50 C 20 C 40 cm

1)

2) 50 C 40 cm 20 C 16 cm

3) 2 C 1) 2)


15

0.2 5x10-7C 5 cm 60


16

12 V/m +3.0 C A C ABC


17

E 4x104 AB BC 10 5 -10-6 A C


18

4 cm -10 C 2, 4 6 cm 6 cm 4 cm


(capacitance)


+Q

-Q

E

E

V

Q V


Q V

Q = CV

C = Q/V

C

(F)


V Q Q V





A d


ra rb


ra

a


(capacitor condenser)



(Series)


(Series)


(Series)


(Parallel)


(Parallel)


2

C1, Q1

C1, Q1

C2, Q2

C2, Q2



1

5 20

2,000


2

A B 6 12 24


4 F, 6 F, 12 F

1)

2)

3) 6 F 12 F 4 F

4) 3. 20

3


4

20 12 30


5

A 2,000 B S A 1,600 A 4.0x10-3F B

S

B

A


A 2 B

6


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