บทที่ 3 กระแสไฟฟ้าและวงจรไฟฟ้ากระแสตรง

1 1 3 2 (ampere) [1 A=1 C/1 s] + q (I) [C/sec] [Ampere] dtdQI AnqvtQId [#/m3] ( e) E3 C s a) b) s QIt = A=Q I t = 5 s 5= C= 10-19 C 10N-== x x x 4 ( )

2 Q n 10 6 m2 A 1028 /m3 I nqvA= 10--= ( ) ~108 m/s IvnqA= 10 m/sv-= 5 F = -eE ( ) (conductivity) ohmic materials 6 (J) dnqvAIJ n = 8x1023 cm-3 vd = cm/s EJ (conductivity)

3 RIALIVLVEAIJLVE ALALR ][1m R q E L A V R R R 7 V/A

4 8 Ohmic material ( ) 9 r l .. cm 10-4 m2 ( 1010 ) 10 .. 2-3 Ohm C Ohm ~100K (-170 C) JR-Maglev at Yamanashi.

5 581 km/h. Guinness World Records authorization 11 0E V ][WattVIdtdqVdtdUPqVU RVRIVIP22 = = 12 power lineIV =2power lineVR =power lineVIR= V A

6 L 2L A B A 2 B P I V =V IR =13 . 60 W 8 hr 5 ( ) 1 A 14 RVRIVIP22 RIV A B i VA VB E VA > VB A B BBAAE dl V I I R r s V V IR=()I R rIr IRee=+-= 15 21212121)(RRRIRVRRIIRIRVIIIss (Serial) R1 V I1 I2 R2 Rs V I 321 RRRRs ?131221 IRRV R1 V R2 I V Rs I AVRIIRRsss3412413 16 b c R1.

7 R2 .. 17 212121111 RRRRVRVRVIIIpp (Parallel) Rp V I R2 V I R1 I2 I1 3211111 RRRRp B R R R A R 6 R A, B R R B A R RP B A 263311111pppRRRRRRR18 .. 6 B A 3 2 4 221189161311111 RRRR1 B A 2 4 A 4 B R2 42212 RRRA RAB B 221141411 ABABABRRR19 5 B A X Y 6 2 1 3 RAB (Kirchhoff s law) 20 1. 2. I1 I2 I3 I1 = I2+I3 I1+ I2=I3 I1 I2 I3 R I () 0() 0 IRIRIR (Kirchhoff s law) I1, I2, I3 21 A 24V 12V 2 6 4 B C D E F 1I2I3IB A 8 V 3 6V 10 13V X Y 1I2I3I22 E B A 24V 12V 2 6 4 B C D E F 1I2I3I RC 2 Q=CV 23 s R C RC VCqV q C I R dtdqRIRV RC I s I CqIR RCqCRCqRdtdqCqdtdqR I(t) =?

8 Q(t) = ? )1()1()(maxRCtRCteQeCtq CQ maxq t 0 RC 2RC 3RC 4RC 24 RCtRCtRCteIeReRCQdtdqI maxmax RI maxI t 0 RC 2RC 3RC 4RC charge C RC = = time constant (second) RC I R s C +Q0 -Q0 C charge Q0 q(t) I(t) s dtdqIandCqIR ( ) RCtQqRCdtqdqRCdtqdqCqRdtdqqQt 00ln0 RCteQq 0 RCteIdtdqI 025 RCteQq 00Qq t 0 RC 2RC 3RC 4RC RC = = time constant (second) RCteIdtdqI 00II t 0 RC 2RC 3RC 4RC I0 = Q0/RC 26 = s R = 200 k C I R s C +Q0 -Q0 I R s MRFCV10212 q/C 8V ( C) charge q/C = 10 V