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All the Physics Formulas in junior high school
（2）、U＝U1＋U2
（3）、R＝R1＋R2
(4) U1 / U2 = R1 / R2 (partial pressure formula)
（5）、P1/P2＝R1/R2
6. Parallel circuit:
（1）、I＝I1＋I2
（2）、U＝U1＝U2
（3）、1/R＝1/R1＋1/R2 [ R＝R1R2/(R1＋R2)]
(4) I1 / I2 = R2 / R1 (shunt formula)
（5）、P1/P2＝R2/R1
7 constant resistance:
（1）、I1/I2＝U1/U2
（2）、P1/P2＝I12/I22
（3）、P1/P2＝U12/U22
8 electric power:
(1) , w = uit = Pt = UQ (universal formula)
(2) W = i2rt = u2t / R (pure resistance formula)
9 electric power:
(1) , P = w / T = UI (universal formula)
(2) , P = I2R = U2 / R (pure resistance formula)
Common physical quantities
1. Speed of light: C = 3 × 108m / S (in vacuum)
2. Sound speed: v = 340m / S (15 ℃)
3. Echo discrimination of human ear: ≥ 0.1s
4. Acceleration of gravity: g = 9.8n/kg ≈ 10N / kg
5. Standard atmospheric pressure value:
760 mm mercury column height = 1.01 × 105 pa
6. Water density: ρ = 1.0 × 103kg / m3
7. Freezing point of water: 0 ℃
8. Boiling point of water: 100 ℃
9. Specific heat capacity of water:
C＝4．2×103J/(kg?℃)
10. Elementary charge: e = 1.6 × 10-19c
11. Voltage of one dry cell: 1.5V
12. Voltage of one lead-acid battery: 2V
13. Safety voltage for human body: ≤ 36V (not higher than 36V)
14. Power circuit voltage: 380V
15. Home circuit voltage: 220 V
16. Unit conversion:
（1）、1m/s＝3．6km/h
（2）、1g/cm3 ＝103kg/m3
（3）、1kw?h＝3．6×106J
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