"Measurement of Resistance" Ohm's Law PPT

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"Measurement of Resistance" Ohm's Law PPT

Part One: Guidance Design

Learning point 1: Principle of measuring resistance

Question: To measure the resistance of a fixed-value resistor as shown in Figure 17-3-11, you generally need to measure the ________ at both ends and the _______ passing through it, and then use the formula _______ to calculate the resistance of the resistor. , this is a _______ (optional "direct" or "indirect") measurement method.

Question 1: For the components shown in Figure 17-3-12, in order to measure the resistance of the fixed-value resistor, the equipment that should be used is: _______________________________________________.

Learning point 2: Measuring the resistance of a fixed value resistor

Question 2: A student wants to measure several more sets of data to see if the measured resistance values ​​are the same. What kind of equipment can be used for this purpose?

answer:___________________.

Question 3: Based on your design ideas, please draw a circuit diagram in the dotted box below, and connect the physical diagram according to the circuit diagram.

Question 4: Carefully analyze the resistance data measured by voltammetry in the table below and see what findings you have?

(1) Based on the measured data and using Ohm’s law, the resistance values ​​of the three resistors are calculated as: ____________________________. (If the calculation result is not divisible, please keep two decimal places)

(2) What are the characteristics of the measured third resistance value?

answer:_____________________________________________.

(3) In the experiment of measuring resistance by voltammetry, what is the method to reduce the measurement error?

answer:__________________________________.

(4) Do you think the resistance of the resistor being measured should be __________Ω.

Learning point 3: Measure the resistance of a small light bulb

Research 1: In order to measure the resistance of the filament when the small light bulb shown in Figure 17-3-15A is normally emitting light, a student designed a circuit diagram as shown in Figure B.

Question 1: Connect the circuit according to the circuit diagram shown in Figure B. Can you measure the resistance of the filament when the small light bulb glows normally? Why?

answer:___________________________________________.

Question 2: In order to measure the resistance of the filament when the small light bulb is emitting light normally, the equipment required is _______________.

Question 3: After closing the switch, the next step is: ____________________________________________, read the ammeter indication, and then calculate the resistance of the filament when the small light bulb emits light normally based on R=.

Exploration 2: After the idea was clear, a student conducted an experiment and used a sliding rheostat to measure the resistance of the small light bulb under different lighting conditions, as shown in the table below:

Question 1: Based on the measured data, use Ohm's law to calculate the resistance values ​​of the four times:_________________________. (If the calculation result is not divisible, please keep two decimal places)

Question 2: What are the characteristics of the fourth-order resistance value?

answer:_______________________________________________________.

Question 3: The brightness of the light bulb indirectly reflects the temperature of the filament. What conclusions can be drawn by comparing the experimental results and related phenomena?

answer:___________________________________.

Resistance measurement PPT, part 2: summary of common exams

Type 1: Resistance value measured by voltammetric method

Typical Example 1 [Xiaogan High School Entrance Examination] In the experiment of "Measuring the resistance of the unknown resistor Rx", please complete the following related questions.

(1) Use pen-drawn lines instead of wires to completely connect the physical circuit in Figure 17-3-9A.

(2) Fill in the corresponding positions in the table with the indications of the voltmeter and ammeter during the second measurement (as shown in Figure B).

(3) Process the experimental data recorded in the table and obtain the resistance value of the unknown resistor Rx as ______Ω.

[Commentary by Famous Teachers] The voltammetry method is used to measure the resistance of a fixed-value resistor. Multiple measurements should be taken during the experiment. The purpose is to find the average of several measurement results to reduce the measurement error.

Type 2: Measure the resistance of small light bulbs using voltammetry

Typical Example 2 - Zhangjiajie High School Entrance Examination - A student used the experimental device shown in Figure 17-3-11A to measure the resistance of a small light bulb.

(1) Please help him use pen-drawn lines instead of wires to connect to the physical circuit. The wires are not allowed to cross.

(2) After the student connected the circuit, he closed the switch and found that the small bulb did not light up, the pointer of the ammeter barely deflected, and the voltmeter showed a reading that was close to the power supply voltage. You think the fault in this circuit might be __________.

(3) After eliminating the circuit fault, the student completed the experiment and plotted the experimental data into an image, as shown in Figure B. When the voltage across the small bulb is 2 V, the resistance of the small bulb is _____Ω.

(4) The student suggested that in the experiment of measuring resistance, the image drawn based on the experimental data was a straight line, but what was obtained in this experiment was a curve. You think the reason may be ____________________.

[Commentary by Famous Teachers] The I-U relationship image of the small light bulb is not a straight line, that is, the resistance of the small light bulb changes. This is mainly because the filament resistance is affected by temperature. The purpose of multiple measurements during the experiment is to obtain Find out how the resistance of a small light bulb changes with voltage (temperature).

Type 3: Other methods to measure resistance

Typical Example 3 There is a thermistor R in the laboratory, and the image of its resistance value changing with temperature is shown in Figure 17-3-13A. To measure the resistance value of the thermistor at any temperature, the following experimental equipment is available: an old dry battery, two switches S1 and S2, and several wires. In addition, the following equipment is available:

A． Ammeter A (range: 0~0.6 A, 0~3 A);

B． Voltmeter V (range: 0~3 V, 0~15 V);

C. Fixed value resistor R1 (resistance: 5 Ω); D. Fixed value resistor R2 (resistance: 150 Ω).

(1) Please choose two pieces of equipment from the four experimental equipments A, B, C, and D to accurately measure the resistance of the thermistor R when the temperature is 32°C, and complete the following questions as required.

①The two pieces of equipment selected are _________ (fill in the alphabetical number in front of the equipment).

②Select the measuring range of the electric meter as _________.

③Draw the experimental circuit diagram based on the existing circuit in Figure B. (The circuit is not disconnected during the experimental measurement process).

④Connect the circuit according to the circuit diagram, write the experimental steps and use letters to indicate the measured physical quantities.

Answer④A． Close switch S1, open switch S2, and read the voltmeter indication as U1; B. Close switches S1 and S2, and read the voltage indication as U2

⑤ Use measured physical quantities and known physical quantities to express R, R = _________.

(2) To accurately measure the resistance of the thermistor R when the temperature is 98°C, the two equipments that can be selected are _______ (fill in the alphabetical number in front of the equipment).

[Commentary by Famous Teachers]In experiments to measure resistance, the volt-ohm method or the ampere-ohm method is often used for variable measurement. It is necessary to use a fixed-value resistor (or rheostat) with a known resistance in series with the resistance being measured. Or in parallel, at this time, you need to pay attention to the "matching" relationship between the two, that is, the resistance of the fixed value resistor (or rheostat) should be equivalent to the resistance being measured, and cannot be far apart, otherwise it will cause their voltage or current distribution to be "unbalanced" .

Resistance measurement PPT, Part 3: Class feedback

1. The principle of measuring resistance by voltammetry is ________. The specific method is to use ________ to measure the voltage at both ends of the resistor to be measured, use ________ to measure the current passing through the resistor to be measured, and then calculate the resistance of the resistor to be measured. value.

2. Draw the circuit diagram for measuring resistance by voltammetry in the dotted box, and connect the physical circuit as shown in Figure 18-1 according to the circuit diagram. When connecting the circuit, the switch should be in the ________ state, and the slider of the sliding rheostat should be at the ________ end. This is mainly to prevent the ________ in the circuit from being too large and burning out the relevant components in the circuit. In the experiment of measuring resistance by voltammetric method, the resistance value of each time is calculated using the formula R=U/I, but the calculated results are often different. This is a _________ in the experiment. It is inevitable and many measures are taken. The method of averaging measurements can be __________________.

[ Analysis For the current of the resistor, measure several sets of data to find the average value of the resistance and reduce the error. When connecting the circuit according to the circuit diagram, the switch should be in the off state, and the resistance of the sliding rheostat should be at the maximum resistance position (depending on the actual connection situation).

3. A classmate pointed out that in the experiment of measuring resistance by voltammetry, the following points must be paid attention to. The one you think is unnecessary is ()

A． Before closing the switch, the slider is at the point of maximum resistance

B． When connecting the circuit, first turn off the switch

C. The switch is connected to the end close to the positive terminal of the power supply

D. The voltmeter is connected in parallel with the resistance to be measured

4. In the experiment of measuring resistance by voltammetry, the role that the sliding rheostat cannot play is ()

A． change the current in a circuit

B． Change the voltage across the resistor being measured

C. Change the resistance of the resistor being measured

D. protect the circuit

5. The students used "voltammetry" to measure the resistance of the unknown resistor Rx. The power supply voltage used was 3 V, and the resistance of Rx was about 5 Ω.

(1) The actual circuit is shown in Figure 18-2A. Please use strokes instead of wires to connect the circuit completely.

(2) After connecting the circuit, close the switch, change the voltage across the resistor Rx, and conduct three measurements. The current value in the third experiment is shown in Figure B, which is __________A.

(3) After processing the experimental data, the average value of the resistance Rx measured three times is __________Ω.

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Update Time: 2024-10-13

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