Learning materials for junior high school physics and electricity!

--Summary of junior high school physics and electricity knowledge.

The circuit is composed of components such as power supply, electric keys, electrical appliances, and wires. For there to be a continuous current in the circuit, there must be a power supply in the circuit, and the circuit should be closed. The circuit has the phenomenon of path, open circuit (open circuit), short circuit of power supply and electrical appliances, etc.

Substances that easily conduct electricity are called conductors. Such as aqueous solutions of metals, acids, alkalis, and salts. Substances that do not easily conduct electricity are called insulators. Such as wood, glass, etc.

Insulators can be converted into conductors under certain conditions.

Identification of series and parallel circuits: series: the current is not bifurcated, parallel: the current is bifurcated.

A method of converting a non-standard circuit diagram into a standard circuit diagram: using the current flow path method. 】

Ten. 1. The law of electric current.

Electricity Q: The amount of charge is called the amount of electricity, unit: coulombs.

Current i: The amount of electricity that passes through the cross-section of a conductor in 1 second is called the current intensity. q=it

Current unit: ampere (a) 1 ampere = 1000 mA The direction in which the positive charge moves in a directional direction is specified as the current direction.

An ammeter is used to measure the current, which is connected in series in the circuit and considers the range to be suitable. It is not allowed to connect the ammeter directly to both ends of the power supply.

Voltage u: The cause of the directional movement of the free charge in the circuit to form the current. Voltage unit: volts (V).

The voltmeter (voltmeter) used to measure the voltage is connected in parallel at both ends of the circuit (electrical appliance, power supply), and the range is appropriate.

Resistance r: The obstructive effect of a conductive object on an electric current. Symbol: r, unit: ohm, kiloohm, megaohm.

The magnitude of the resistance is directly proportional to the length of the wire, inversely proportional to the cross-sectional area, and is also related to the material. 【

The conductor resistance is different, and when connected in series in a circuit, the current is the same (1 1). The conductor resistance is different, and when connected in parallel in a circuit, the voltage is the same (1:1).

Ohm's Law: Formula: i u r u ir r u i

The intensity of the current in the conductor is directly proportional to the voltage at both ends of the conductor and inversely proportional to the resistance of the conductor.

Conductor resistance r u i. If the voltage of a given conductor changes, the current also changes, but the resistance value does not change.

Series circuit features:

i＝i1＝i2 ② u＝u1＋u2 ③ r＝r1＋r2 ④ u1／r1＝u2／r2

When two conductors with different resistances are connected in series, the voltage at the two ends with the greater resistance is larger, and the conductor with the smaller voltage at both ends has less resistance.

Example: How to connect a lamp marked with "6V, 3W" to a circuit marked with 8 volts to make the small bulb glow normally?

Solution: Since p 3 watts, u 6 volts.

i p u 3 watts 6 volt amperes.

Since the total voltage of 8 volts is greater than the rated voltage of the lamp 6 volts, a resistor r2 should be connected in series as shown in the figure on the right, so u2 u u1 8 volts 6 volts 2 volts.

R2 U2 I 2 volt-ampere 4 ohms. A: (omitted).

Parallel circuit features:

U U1 U2 I I1 I2 1 R 1 R1+1 R2 or I1R1 I2R2

The daily power consumption of the refrigerator nameplate is, the refrigerator works for 12 minutes each time, that is, 12 60 = the refrigerator power is 150w, and the power consumption of the refrigerator from start to stop is 150 * then the refrigerator works n = times per day. The actual working hours are:

The number of revolutions of each meter m =

Well, there is an error in the calculation of the number of times, and I found that there was a mistake in my thinking after referring to the answer upstairs, and corrected it.

This should be the actual daily electricity consumption, divided by the electricity consumption per job:

Thank you for the other two corrections, suggesting the answer from jiusi2001.

The answer of jius2001 is correct. Because the refrigerator doesn't work 24 hours a day.