Twenty-six electrical formulas of junior high school physics 1, current intensity: I=Q electricity /t
2. Resistance: R=ρL/S
3. ohm's law: I=U/R
4, Joule's law:
(1)Q=I2Rt general formula)
(2)Q=UIt=Pt=UQ =U2t/R (pure resistance formula)
5, series circuit:
( 1)I=I 1=I2
(2)U=U 1+U2
(3)R=R 1+R2
(4)W=UIt=Pt=UQ (universal formula)
(5)W=I2Rt=U2t/R (pure resistance formula)
(6)U 1/U2=R 1/R2 (partial pressure formula)
(7)P 1/P2=R 1/R2
6, parallel circuit:
( 1)I=I 1+I2
(2)U=U 1=U2
(3) 1/R = 1/R 1+ 1/R2[R = R 1r 2/(R 1+R2)]
(4)I 1/I2=R2/R 1 (shunt formula)
(5)P 1/P2=R2/R 1
7. Fixed value resistance:
( 1)I 1/I2 = u 1/U2
(2)P 1/P2=I 12/I22
(3)P 1/P2=U 12/U22
8. Electricity:
(1)W=UIt=Pt=UQ (general formula)
(2)W=I2Rt=U2t/R (pure resistance formula)
9. Electricity:
(1)P=W/t=UI (general formula)
(2)P=I2R=U2/R (pure resistance formula)
Junior Middle School physical and electrical Formula and Life (1) Family Circuit
Composition: electric energy meter, master switch, fuse box, switch and socket.
Connection: All lamps, electrical appliances and sockets are connected in parallel. The electric lamp is connected in series with the switch that controls it.
Household circuit voltage: 220V.
Causes of excessive current in household circuits: short circuit and excessive total power of electrical appliances.
Fuse: made of lead-antimony alloy with high resistivity and low melting point. Connecting it in series in the circuit can ensure that the circuit will automatically cut off before the current in the circuit increases to a dangerous level.
(2) Safe use of electricity
Safe voltage of human body: not higher than 36V.
Principle of safe electricity use: Don't touch low-voltage charged body and don't approach high-voltage charged body.
Fire and zero lines can be detected with a pencil.
(3) Simple magnetic phenomena
Magnetism: the property that an object can attract iron, cobalt, nickel and other substances.
Pole: The most magnetic part of a magnet. A magnet has two magnetic poles, namely the South Pole (S Pole) and the North Pole (N Pole).
Interaction between magnetic poles: magnetic poles with the same name repel each other and magnetic poles with different names attract each other.
(4) Magnetic field
There is a magnetic field around the magnet. The basic characteristic of magnetic field is that it exerts a powerful effect on the magnet put in it.
Magnetic field direction: the direction of the north pole when the small magnetic needle at a certain point in the magnetic field is at rest, which is defined as the magnetic field direction at that point.
Magnetic induction line: Some directional curves drawn in a magnetic field. The tangent direction of any point on the curve is consistent with the north pole of the small magnetic needle placed at that point.
The magnetic induction line outside the magnet comes out from the north pole of the magnet and returns to the south pole of the magnet.