"Special Method to Measure Resistance" Ohm's Law PPT

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"Special Method to Measure Resistance" Ohm's Law PPT

【Topic Overview】

Common special methods for measuring resistance include volt resistance method, ampere resistance method and substitution method. The specific measurement methods are as follows:

(1) Measuring resistance by voltresistance method refers to the method of measuring unknown resistance using a voltmeter and a known resistance. As shown in the figure is the circuit diagram for measuring resistance by voltresistance method. First, connect the voltmeter to both ends of the known resistance R, and record the indication U1 of the voltmeter at this time; then connect the voltmeter to both ends of the unknown resistance Rx. Note down the voltmeter indication U2 at this time. According to Ohm's law, the current through the two resistors I1=U_1/R, I2=U_2/R_x. Since R and Rx are connected in series, I1=I2, that is, U_1/R=U_2/R_x, Rx=U_2/U_1 R.

(2) Measuring resistance by the ampereometric method refers to the method of measuring unknown resistance using an ammeter and a known resistance. As shown in the figure is the circuit diagram for measuring resistance by the ampereometric method. First, connect the ammeter in series with the known resistor R, and measure the current I1 through R; then connect the ammeter in series with the unknown resistor Rx, and measure the current I2 through Rx. Calculate the voltages at their respective ends U1=I1R, U2=I2Rx according to Ohm's law; since R and Rx are connected in parallel, U1=U2, that is, I1R=I2Rx, Rx=I_1/I_2 R.

(3) The circuit for measuring resistance using the substitution method is as shown in the figure. In the figure, R is a sliding rheostat, R' is a resistance box, Rx is the resistance to be measured, S2 is a single-pole double-throw switch, and G is an ammeter.

Adjust the slider P to the lowest end of the sliding rheostat in the circuit diagram, adjust the resistance box R' to the maximum value, close the switch S1, move the switch S2 to position "1", adjust the position of P, and make the ammeter point to a suitable Scale IG; then move the switch S2 to position "2", keep the position of the slider P unchanged, and adjust the resistance value of the resistance box R' so that the scale indicated by the ammeter is still IG. At this time, the resistance value of the resistance box is R0, then Rx=R0.

Type 1: Measure resistance by volt resistance method

1. When measuring the unknown resistance Rx by voltammetry, if the ammeter is missing or damaged, it can also be solved by other methods. Among the following four figures, the one that can complete the task is (B)

2. (Suihua High School Entrance Examination) Figure A is a physical circuit in which the experimental team used voltammetry to measure the unknown resistance Rx. The power supply voltage is unknown but constant. The maximum resistance of the sliding rheostat is known to be R (resistance is not affected by temperature).

(1) Find a wrongly connected wire in Diagram A, and draw an " cannot cross);

(2) When connecting the circuit, the switch should be turned off, and the sliding blade of the sliding rheostat should be located at the right (optional "left" or "right") end;

(3) The principle of this experiment is R=?/? (or Ohm’s law);

(4) During the experimental operation, it was found that the ammeter was damaged but the voltmeter was intact, so the students in the group designed the circuit diagram as shown in Figure B and completed the experiment. Please help them complete the following experimental steps:

① Close the switch S and adjust the sliding plate of the sliding rheostat. When the sliding plate is at the leftmost end, read the voltmeter indication at this time and record it as U1;

②Move the slider to the far right, read the voltmeter indication at this time, and record it as U2;

③Then the unknown resistance Rx= ?_2/(?_1 "−" ?_2 )R　.

Type 2: Resistance measurement using the ampereometric method

3. When measuring the unknown resistance Rx using voltammetry, it was found that the voltmeter was damaged. A student designed the following four plans. The correct one is (D)

4. Xiao Ming uses the circuit shown in Figure A to measure the resistance of a small light bulb with a rated voltage of 2.5 V. Figure B is the experimental circuit Xiao Ming connected.

(1) After Xiao Ming has connected the circuit correctly, he closes the switch and adjusts the slider of the sliding rheostat so that the small bulb just glows normally. At this time, the ammeter reads as shown in Figure C. The ammeter reads 0.3 A. The resistance of the small bulb The value is 8.3Ω (one decimal place is retained);

(2) When the voltage value changes, the resistance of the small bulb changes (optional "change" or "unchanged"). The basis for your judgment is that the resistance of the small bulb is affected by temperature;

(3) Xiao Ming wanted to measure the resistance of an unknown resistor Rx, and designed the circuit as shown in Figure D (R0 is a fixed-value resistor with a known resistance), and designed the following experimental steps. Please help him with the missing steps. Complete and write the expression for Rx.

Experimental steps:

A. Connect the circuit according to the designed circuit diagram (such as Figure D);

B. Open S2, close S1, and record the current as I1;

C. Open S1, close S2, and record the current as I2;

Expression: Rx= (?_1 ?_0)/?_2 (expressed in symbols of known and measured physical quantities).

Type 3 Equivalent substitution method for measuring resistance

5. To measure a resistor Rx with a resistance of about 600 Ω, the equipment provided: two dry batteries, a student voltmeter (with a range of 0~3 V, 0~15 V), and a student ammeter (with a range of 0~0.6 A. (A), one sliding rheostat (10 (A)) and one resistance box R0 (0~9999 (A), and several switches and wires. Among the following four design solutions, which one can measure the Rx resistance is the most reasonable one Yes(D)

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Update Time: 2024-11-01

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