"Measurement of Resistance" Ohm's Law PPT Courseware 3

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"Measurement of Resistance" Ohm's Law PPT Courseware 3

Review the past and learn the new

1. The indication of a voltmeter connected in parallel at both ends of the wire is:

2. A voltmeter connected in series in the circuit shows:

1. Three basic physical quantities of circuits:

Physical quantity: current I, measuring tool: ammeter (ammeter)

Physical quantity: voltage U, measuring tool: voltmeter (voltmeter)

Physical quantity: resistance R, measuring tool: ?

2. Ohm’s law

Content: The current in a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.

Expression: I =U/R

Variations: U=IR, R=U/I

1. Measure resistance by voltammetry

Experiment purpose: Use voltmeter and ammeter to measure resistance indirectly

Experimental principle R=U/I

Experimental equipment: power supply, voltmeter, ammeter, sliding rheostat, switch, wire, resistance to be measured.

Experimental requirements

1. Write out your experimental procedures and experimental data recording forms;

2. Connect the circuit according to the circuit diagram and make measurements;

3. Record the measured data in a record sheet designed by you;

4. Based on the measured data, calculate the resistance value using Ohm's law;

5. Measure several sets of data to see if the measured resistance values ​​are the same.

Experimental steps

1. Adjust the pointers of the ammeter and voltmeter to zero scale; connect the physical objects according to the circuit diagram. Adjust the sliding rheostat to the maximum resistance end;

2. Close the switch, adjust the sliding blade of the sliding rheostat to the appropriate position, read the ammeter reading I and the voltmeter reading U respectively, and record them in the table;

3. Calculate the value of R according to the formula R=U/I and record it in the table.

4. Adjust the slider of the sliding rheostat to change the current in the resistance to be measured and the voltage at both ends, then measure several sets of data, and calculate the average value of R.

Precautions

1. Before connecting the circuit, adjust the ammeter and voltmeter to zero scale.

2. When connecting the circuit, the switch should be turned off. After connecting the circuit, the sliding rheostat should be adjusted to the maximum resistance end.

3. Connect the circuit, use the switch to test after checking that the circuit connection is correct, and then close the switch S after confirming that the circuit is intact.

4. Pay attention to selecting appropriate ranges for voltmeters and ammeters.

Think about it, do it

1. Replace the fixed-value resistor in the above experiment with a small light bulb and use the same method to measure the resistance of the small light bulb.

2. Measure several sets of data and calculate the resistance of the small light bulb based on the experimental data;

3. Compare the calculated values ​​to see if the resistance values ​​calculated are the same each time? Is there any pattern of change?

4. If the situation that occurs is different from when measuring a fixed value resistance, how do you explain it? Talk to your classmates.

Circuit connection:

Fault 1: The pointers of the ammeter and voltmeter deflect in opposite directions.

Judgment: The "+" and "-" terminals of the ammeter and voltmeter are connected reversely.

Fault 2: The pointer deflection angle of the ammeter and voltmeter is very small.

judge:

①The ranges of the voltmeter and ammeter may be selected too large;

②The power supply voltage may be too low.

Fault 3: The ammeter pointer exceeds the maximum value.

judge:

①The measuring range may be selected too small;

② There may be a short circuit in the circuit.

Fault 4: When the sliding rheostat slides, the electric meter and the brightness of the bulb do not change.

Judgment: The sliding rheostat does not have a "one up and down" connection.

Example explanation:

Example 1. The following equipment is available: ammeter (0-0.6A 0-3A), voltmeter (0-3V 0-15V), sliding rheostat (0-10 ohm 2A), 4V power supply, and a small light bulb with resistance to be measured ( The normal light-emitting voltage is 2.5V, the resistance is about 6 ohms), a switch and some wires. It is required to use voltammetry to measure the resistance of the filament when the small light bulb is normally emitting light. During the measurement, the pointers of the two meters should deviate from the center line of the surface scale.

(1) Try to draw the circuit diagram;

(2) The measuring range of the ammeter should be 0-0.6A and the measuring range of the voltmeter should be 0--3V;

(3) The reasonable order of the following steps is E F G AH D B E C.

A Close the switch B Fill in the measured data into the table

C Calculate the resistance of the small bulb under test D Read the indications of the two meters

E Turn off the switch F Adjust the resistance of the sliding rheostat to the maximum position

G Connect the circuit according to the circuit diagram

H Adjust the sliding rheostat so that the voltage indication is 2.5V

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Update Time: 2024-08-31

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