"Measurement of Resistance" Ohm's Law PPT Courseware 4

Description

"Measurement of Resistance" Ohm's Law PPT Courseware 4

learning target

1. Further master the method of using voltmeter and ammeter

2. Learn to measure resistance using voltammetry

3. Deepen your understanding of Ohm’s law and its applications

Want to discuss

How to use Ohm's law to find a way to indirectly measure the resistance of a conductor?

I =U/R R=U/I

This formula uses a ratio to define the resistance of a conductor. It is a calculation formula for resistance, not a determining formula. It provides us with a method of measuring resistance, called voltammetric measurement of resistance.

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.

What is the function of a rheostat in a circuit?

① Reduce the experimental error by changing the current in the circuit and the voltage across the bulb and averaging multiple measurements.

②Protection circuit

The ammeter and voltmeter are used to measure the current I through the bulb and the voltage U across it respectively. What is the function of a rheostat in a circuit?

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 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.

Note: The highest voltage across the small bulb is the voltage value marked on the small bulb!

Discussion and exchange

1. Are the resistances of small light bulbs the same under various voltages? Which one is larger?

2. Think about the reasons for the difference?

in conclusion

The resistance value of the light bulb is related to the change of the temperature of the light bulb. The higher the temperature, the greater the resistance

Consolidation exercises

1. When using a voltmeter and ammeter to measure resistance, the basis is ______; if the voltmeter and current are known as shown in the figure, the voltmeter reading is _____, the ammeter reading is _____, and the measured resistance is _____.

2. A small light bulb with a rated voltage of 3.8V, Xiao Ming measured its resistance at 1.2V, and then adjusted the voltage across the bulb to 3.8V to measure its resistance. Xiao Ming found that the resistance at the last time was much greater than the first time. This is because( )

A. The experimental method is wrong

B． Experimental error

C. The resistance of a conductor is related to temperature

D. experimental error

3. As shown in the figure, the power supply voltage remains unchanged. After the switch is closed, if P moves to the right, the changes in the voltmeter and current indications are ( )

A. The voltage indication number becomes larger and the current indication number becomes smaller.

B. The voltage indication number becomes larger and the current indication number becomes larger

C. The voltage indication number becomes smaller and the current indication number becomes larger.

D. The voltage indication number becomes smaller and the current indication number becomes smaller

4. In the circuit as shown in the figure, the power supply voltage is 6V. After the switch S is closed, the lamp L does not light up. The voltage across resistor R measured with a voltmeter is 6V, which means: ( )

A. The lamp L and the resistor R are both intact

B. Lamp L is intact but resistor R is broken.

C. The lamp L is broken and the resistor R is intact.

D. Both the lamp L and the resistor R are open circuit

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For more information about the "Ohm's Law Measurement of Resistance" PPT courseware, please click the Ohm's Law ppt Measurement of Resistance ppt tag.

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Update Time: 2024-11-13

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