1. The series circuit current and voltage have the following laws:
(Such as: R1, R2 in series)
①Current: I=I1=I2 (the currents in all parts of the series circuit are equal)
②Voltage: U=U1+U2 (the total voltage is equal to the sum of the voltages of various places)
③Resistance: R=R1+R2 (total resistance is equal to the sum of each resistance) If n resistors with the same resistance value are connected in series, then Rtotal = nR
2. Parallel circuit current and voltage have the following laws:
(For example: R1, R2 are connected in parallel)
①Current: I=I1+I2 (the main circuit current is equal to the sum of the current of each branch)
②Voltage: U=U1=U2 (the voltage of the main circuit is equal to the voltage of each branch)
③Resistance: (the reciprocal of the total resistance is equal to the sum of the reciprocal of the parallel resistances) or if n resistors with the same resistance are connected in parallel, then Rtotal = R
Note: The total resistance of the parallel circuit is smaller than the resistance of any branch.
3. Electric power calculation formula:
(1) W=UIt (in the formula, the unit is W→Joke (J); U→Volt (V); I→A (A); t→second)
note:
①W, U, I and t in the formula are in the same circuit
②Units should be unified when calculating
③ Knowing any three quantities, the fourth quantity can be obtained.
(2) The following formula can also be used to calculate electric power: W=I2Rt; W=Pt; W=UQ (Q is electricity)
【Electrical part】
1. Current intensity: I=Q power/t
2. Resistance: R=ρL/S
3. Ohm’s law: I=U/R
4. Joule’s law:
Voltage = current * resistance that is U = RI
Resistance=Voltage/Current ie R=U/I
Power = current * voltage that is P = IU
Electric energy = electric power * time that is W = Pt
Sign meaning and unit
U: Voltage, V
R: Resistance, Ω
I: current, A
P: Power, W
W: Electricity, J
t: time, S
⑴、Q=I2Rt universal formula)
⑵, Q=UIt=Pt=UQ power=U2t/R (pure resistance formula)
5. Series circuit:
⑴、I＝I1＝I2
⑵、U＝U1＋U2
⑶, R＝R1＋R2
⑷、U1/U2=R1/R2 (partial pressure formula)
⑸、P1/P2=R1/R2
6. Parallel circuit:
⑴、I＝I1＋I2
⑵, U＝U1＝U2
⑶, 1/R＝1/R1＋1/R2 [R＝R1R2/(R1＋R2)]
⑷、I1/I2=R2/R1 (shunt formula)
⑸、P1/P2=R2/R1
7. Fixed value resistance:
⑴、I1/I2=U1/U2
⑵、P1/P2=I12/I22
⑶, P1/P2=U12/U22
8. Electric power:
⑴、W＝UIt＝Pt＝UQ (universal formula)
⑵、W＝I^2Rt＝U^2t/R (pure resistance formula)
9. Electric power:
⑴、P=W/t=UI (universal formula)
⑵, P＝I2^R＝U^2/R (pure resistance formula)
10. Partial pressure formula
It is a formula for calculating how to divide the total voltage of each resistor in series and how much voltage is divided into. How much of the sub-voltage is calculated as follows: the percentage of the total resistance is the percentage of the sub-voltage.
The formula is: U = (R/R total) × U source
For example, 5 ohms and 10 ohms resistors are connected in series in the middle of a 10V circuit, 5 ohms account for 1/3 of the total resistance of 5 + 10 = 15 ohms, so its divided voltage is also 1/3, which is 10/3 volts.
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