Examination of 22 physics senior high school entrance examinations in Huanggang. Xiao Yang designed a natural gas leakage detection circuit, as shown in Figure A, where R is the gas sensitive resistor

Examination of 22 physics senior high school entrance examinations in Huanggang. Xiao Yang designed a natural gas leakage detection circuit, as shown in Figure A, where R is the gas sensitive resistor. Answer d

Test center/site

1. Series voltage division (options A and B)

2. Dynamic circuit (question type: according to the change of voltmeter current)

analyse

A: With the increase of natural gas concentration, it can be seen from the image that R decreases. According to the fact that the voltage distribution in series circuit is proportional to the resistance, the partial pressure of R decreases. Since the total voltage remains the same, the divided voltage of R0 increases the resistance.

B: With the decrease of natural gas concentration, R becomes larger. Because R0 remains unchanged, the total series resistance becomes larger. Because the total voltage is constant, the total current becomes smaller, that is, the current representation becomes smaller.

C: With the increase of natural gas concentration, R decreases and the total series resistance decreases. When the total voltage remains constant, the total current increases. According to P=UI, it can be seen that the total power becomes larger.

You can also use P=U? /R (pure resistance circuit) The total voltage is constant, the total resistance becomes smaller and the total power changes (P is inversely proportional to R).

D: Natural gas concentration decreases, R increases, and partial pressure increases, resulting in smaller voltage expression; Because the total resistance becomes larger, the current representation becomes smaller; That is, the voltmeter and ammeter become smaller, but because U0/I0=R0, R0 remains unchanged, so the ratio remains unchanged; That is, the voltage and current at both ends of the constant resistance in series circuit change in the same direction, but the ratio is the resistance itself, so the ratio remains unchanged.