일반물리 2Introduction

• 송 석호 교수

– 자연과학대학 401호

– 02-2220-0923

– shsong@hanyang.ac.kr

– http://optics.hanyang.ac.kr/~shsong

• References

– http://iphysics.chonbuk.ac.kr/ - 전북대학교 물리학과

– http://www-ph.postech.ac.kr/genphys/gp/ -포항공대

– http://online.physics.uiuc.edu/courses/phys101/

21. 전하 (charges)

•종류 : 두종류가있으며, (+)전하와 (-)전하로나타낸다.

•양자화: 전하량은최소단위가있다 (양자화되어있다).

•보존 : 총전하량은언제나같다 (보존된다).(전하가생길때부호가반대인전하도동시에똑같은양이생긴다; 사라질때도같다.)

(Coulomb) 10602.1 ,3 ,2 ,1 ,

19Cenneq

−×=

±±±== L

) ( )(

생성쌍

소멸과정+−

+−

+→

+→+

eeee

γ

γγ

21-3. 도체와 절연체

전기전도 특성에 따른 물체의 분류

• 도체 (conductors)

• 반도체 (semiconductors)

• 절연체(유전체) (insulators, dielectrics)

▸ 초전도체(superconductors)

그 속에서 전하가 움직일 때 저항이 없는 물질

[어느 온도(상전이온도) 이하에서만 초전도성을 띤다.]

Conductors and Insulators

Most things are in between perfect conductor / insulator

Electrons in a conductor

Electrons in an insulator

• Charging by Induction

Grounded

Conductor

Charges are uniformly distributed at the surface of conductors.

Induced Charge due to polarization in insulators.

유도 전하 (Induced charge)

유도 전하 (Induced charge)

전도 전자유도 전하

유도 전하

확인문제 1

21-4. Coulomb 법칙

같은 부호의 전하는

서로 밀어내고

다른 부호의 전하는서로 당긴다

04

12

21 >=rqqF

oπε

04

12

21 <=rqqF

oπε

# Vector notation of Coulomb’s Law

r̂rqqkF eC 2

21=r

21221

12 r̂rqqkF e=

r

12221

21 r̂rqqkF e=

r

1221 r̂r̂ −=

1221 FFrr

−= : Newton’s third law

The magnitude is the same but the direction is opposite.

+ –

+−

q1 q2

q3q4

12Fr13F

r

14FrVector Sum

∑=++=i

iFFFFF 11413121

rrrrr

전기력과 중력

221

41

rqqF

oC πε=

221

rmmGFG −=

거리의제곱에반비례

+ (반발력), – (인력) 항상 – (인력)

껍질정리항상성립

(예) 수소원자 (Hydrogen Atom) 에서의 전기력과 중력 비교

+- e

p

Average separation r = a0 = 5.3 × 10-11m|e| = 1.60 × 10-19Cmp = 1.67 × 10-27kg , me = 9.11 × 10-31kg

( )( )211

219

2

29

221

10351060110998

m.C.

CmN.

rqqkF ee −

−

×

×⋅×==

Electrical force

N. 81028 −×=

( )211

2731

2

211

221

103510671101191076

m.kg.kg.

kgmN.

rmmGFG −

−−−

×

×⋅×⋅×==

Gravitational force

N. 471063 −×=

+ --

Positive charge is attracted (force to left)Negative charge is repelled (force to right)Positive charge is closer so force to left is larger.

A positive and negative charge with equal magnitude are connected by a rigid rod, and placed near a large negative charge. What is the net force on the two connected charges?

1) Left 2) Zero 3) Right

221

rqkqF =

Question

1) Nothing2) Attracted to charged sphere.3) Repelled from charged sphere.

• An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released?

Question

(1) Negative charge attracts + repels -(2) Since + is closer, attractive force is strongest

Summary

•종류 : 두종류가있으며, (+)전하와 (-)전하로나타낸다.

•양자화: 전하량은최소단위가있다 (양자화되어있다).

•보존 : 총전하량은언제나같다 (보존된다).

• Coulomb의법칙

(Coulomb) 10602.1 ,3 ,2 ,1 ,

19Cenneq

−×=

±±±== L

r̂rqqkF eC 2

21=r

∑=++=i

iFFFFF 11413121

rrrrr