# Such electrical problems are not a problem for the top students.Fills up the topic of 22

2022-06-16 By The 2021 cD-physics and electrics-filling-blanks question for middle school students is a bit difficult, and it is not easy for average students to get full marks, but for students with good grades, it is not a problem because they can grasp the key points to solve the problem.Let’s take a look at this trick.Analysis :(1) after closing the switch S, the small bulb L does not emit light and the ammeter shows no number, indicating that there is no current in the circuit and the fault type is open;If the voltmeter is displayed, both ends of the voltmeter are properly connected to both ends of the power supply.In summary, it can be determined that the circuit fault is R break.(2) the resistance of the small bulb RL: RL=UL2/PL= (2.5V) 2/1.25W=5 ω;Current when the bulb works normally: IL = PL/UL=1.25W/2.5V=0.5A;At this time, the indicator of the voltmeter is 2V, and the small bulb, voltmeter, ammeter and sliding rheostat all work normally. 0.5A is the maximum current allowed by the circuit.When the resistance in the sliding rheostat access circuit reaches the maximum value of 10 ω, the voltage at both ends of the sliding rheostat is known as 2×4.5V/3=3V according to the voltage division law of the series circuit, which does not exceed the range of the voltmeter. At this time, the current in the circuit is the smallest, and the minimum value Imin is:Imin = U/ (Rm+RL) =4.5V/ (10+5) ω =0.3A.Therefore, the range of current representation is 0.3a ~ 0.5A.A. cut off B. cut off C. cut off D. cut off0.3 A to 0.5 A.The first question in this question is not big and most of the examinees can answer it correctly.The second empty requirements to ensure the safety of each component of the circuit, the entry point is the small bulb normal light, this is the maximum current in the circuit.Moving the sliding vane of the sliding rheostat increases the resistance value in the access circuit, but cannot exceed the range of the voltmeter. Through the calculation of the law of voltage division, it is known that when the resistance in the access circuit of the sliding rheostat reaches the maximum value of 10 ω, the number of the voltmeter is 3V, which just does not exceed the range.This, not every examinee can calculate smoothly come out.Happy teachers and students!Ninth grade physics chapter review, difficulty analysis, test and analysis ye teacher physics 99 yuan to buy column