"Measurement of resistance by "voltammetry"" Exploring Circuit PPT Courseware 3

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"Measurement of resistance by "voltammetry"" Exploring Circuit PPT Courseware 3

What physical quantities have we learned so far about electricity?

How to measure the resistance of a small light bulb

I =U/R R=U/I

R=U/I means that the resistance of a conductor is numerically equal to the ratio of the voltage applied to both ends of the conductor to the current flowing through it. This formula uses a ratio to define the resistance of a conductor. It is a definition of resistance, not a determinant. It provides us with a method of measuring resistance, which is called voltammetric measurement of resistance.

1. Measure resistance by voltammetry

Purpose of experiment: Use voltmeter and ammeter to indirectly measure resistance

Experimental principle R=U/I

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

Think about it?

What is the function of sliding rheostat?

effect:

① By changing the resistance in the circuit, gradually change the current in the circuit and the voltage across part of the circuit

②Protection circuit

What should you pay attention to before the experiment?

1. What state should the switch be in?

2. In order to protect the safety of circuit equipment, what measures should be taken during the experiment?

3. What method is used to determine the range of ammeter and voltmeter?

Experimental steps:

1) Disconnect the switch and connect the circuit

2) Adjust the sliding rheostat connected to the circuit to the maximum

3) Close the switch, adjust R, read and record several sets of ammeter and voltmeter data (U≤U amount)

4) Calculate the resistance of the small light bulb

practice

1. A small light bulb with a rated voltage of 3.8V. Xiao Ming measured its resistance at 1.2V, and then adjusted the voltage at both ends of the light bulb to 3.8V to measure its resistance. Xiao Ming found that the resistance at the last time was greater than the first time. Much more, 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

2. A 20 resistor is connected to a power supply consisting of 4 dry batteries connected in series. To measure the current in this resistor and the voltage at both ends, the selected range of the ammeter and voltmeter should be ( )

A. 0～0.6A, 0～3V B． 0～0.6A, 0～15V

C. 0~3 A, 0~3 V D. 0~3 A, 0~15 V

3. After a student connected the experimental equipment with the circuit shown in the figure, he closed the switch. The light bulb glowed normally, but the voltmeter pointer did not move. This may be ()

A. The ammeter is burned out and the circuit is open

B． The ammeter is intact, but the wire connected to the ammeter is broken.

C. Short circuit in the wire at the voltmeter terminal

4. In the experiment of "measuring the resistance of a small light bulb", a student accidentally connected the ammeter and voltmeter in the wrong position when connecting the circuit, as shown in the figure. Possible phenomena when closing the switch are ( )

A. The ammeter is burned out and the voltage indication is 0

B． Small light bulb burned out

C. The current representation number is 0, and the voltage representation number is the power supply voltage value.

D． The current representation number is 0, and the voltage representation number is 0

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Update Time: 2024-11-25

This template belongs to Physics courseware Shanghai Science Edition Ninth Grade Physics industry PPT template

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