And knowledge points

And knowledge points

1. When the "220 V 40 W" and "220 V 60 W" electric lamps are connected in series in a 220 V circuit, their actual power is calculated
2. With the improvement of people's living standards, refrigerators have entered thousands of households. It is known that the rated power of a household refrigerator is 120W, and the working time of the refrigerator is not continuous. If the total working time of the refrigerator is 6h, how many kilowatt hours of electricity is consumed
3. Resistance R1 = 4 ohm, R2 = 8 ohm in series in the 24 V circuit, at this time, the electrical power of R1?
4. An electric iron needs a certain preheating time before it is used, so people often connect it to the power supply when it is not in use, which not only wastes electricity, but also causes the iron head to be oxidized and not easy to be stained with zinc. Xiao Ming connects an electric iron marked "220 V 55 W" with a bulb (the resistance of the bulb in the preheating state is 495 Ω) to form the circuit diagram as shown in the figure, The soldering iron soon reaches the welding temperature
What is the power consumption of electric iron in 1 'preheating state
The power consumption of the whole circuit in 2 'preheating state is several percent of that of the electric iron in normal operation
——————Electric soldering iron——
↑ |
220V ___ Switch__ |
↓ | | |
————- light bulb————

About Ohm's law and electric power
R1 and R2 are two constant resistors, R1: R2 = 1: n. The small bulb L is marked with 6V and 3W. When l is connected in series with R1, the small bulb will light normally. When the small bulb is connected in series with R2, the power consumed by the small bulb is one fourth of the rated power
(1) If n is a positive integer less than 5, the possible value of n is explained by calculation
(2) Try to find the corresponding resistance of R1 and R2 when n is the above possible value

Set the resistance value of the bulb as RL, there is
Light bulb and R1 in series RL * (V / (R1 + RL)) ^ 2 = 3 (1)
Lamp connected in series with R2 RL * (V / (R2 + RL)) ^ 2 = 3 / 4 (2)
From 3W = 6V × 6V / RL, RL = 12
The known condition is R2 = n × R1
(1) If (n-2) r1-12 = 0
The solution shows that n has two values that meet the constraint conditions, namely 4 and 3
When n = 4, R1 = 6, R2 = 24, the voltage source should be 9V;
N = 3, R1 = 12, R2 = 36, the voltage source should be 12V

As shown in the figure, the voltage of the power supply is 6V, the resistance R1 = 5 Ω, and the maximum resistance of the rheostat R2 is 10 Ω

(1) When the slide is at the B end, the number of current indication is the smallest, I min = ur1 + R2 = 6v5 Ω + 10 Ω = 0.4A, at this time, the number of voltage indication is the smallest, u min = I min, R1 = 0.4A × 5 Ω = 2V; (2) when the slide is at the a end, the number of current indication is the largest, I max = ur1 = 6v5 Ω = 1.2A, at this time, the number of voltage indication is the largest, u max = u = 6V, so the indication range of the ammeter is 0.4A ≤ I ≤ 1.2A, and the indication of the voltmeter changes The indication range of ammeter is 2V ≤ u ≤ 6V; a: the indication range of ammeter is 0.4A ≤ I ≤ 1.2A, and that of voltmeter is 2V ≤ u ≤ 6V

Under what conditions, according to the calculation formula of electric power and Ohm's law, we can deduce the formula of electric power expressed by voltage resistance (i.e. P = u ^ 2 / R)~
Such as the title
In________________ Based on the formula of electric power (P = UI) and Ohm's Law (U = IR), the formula of electric power expressed by voltage and resistance (P = u ^ 2 / R) can be deduced?
The whole topic is a circuit with a single pole double throw switch. When a is connected, there is only one resistor R1, voltage is 110V, and road power is 1100W. When B is connected, there is only one resistor R2, voltage is 220V, and circuit power is still 1100W. Then the first question is________________ Based on the calculation formula of electric power (P = UI) and Ohm's Law (U = IR), the formula of electric power expressed by voltage and resistance (P = u ^ 2 / R) ～

Pure resistance circuit