This is a common method for measuring resistance. Because the voltage (in volts) is divided by the current (in amperes), it is called voltammetry.
This explanation is more formal and easier to understand. You can think of it as a method of calculating resistance by using the experimental circuit diagram of ohm's law, measuring voltage with voltmeter and measuring current with ammeter
Today, we will take a concrete look at the two experiments of measuring resistance by voltammetry and measuring the resistance of small bulbs by voltammetry.
1. Voltammetry to measure the resistance of resistance resistor.
1, experimental principle: according to the deformation formula of ohm's law, r = u/i.
As long as the voltage across the constant resistance and the current flowing through it are measured, its resistance can be calculated.
2. Experimental equipment: power supply, switch, ammeter, voltmeter, sliding rheostat, resistor to be measured and several wires.
3. The function of sliding rheostat is to change the voltage across the measured resistor and protect the circuit.
4, experimental circuit diagram, physical diagram
5. Experimental steps
① Connect the circuit correctly according to the circuit diagram (turn off the switch and move the sliding vane of the sliding rheostat to the place with the largest resistance).
(2) After the inspection is correct, close the switch, adjust the position of the sliding vane P of the sliding rheostat, change the voltage at both ends of the resistor to U 1, U2 and U3 respectively, observe the corresponding value of the ammeter every time, and fill in the design record forms of I 1, I2 and I3 respectively:
(3) According to the voltage and current values recorded each time, find out their corresponding resistance values, and then find out their average values.
5. The purpose of repeated experiments:
Take the average of many measurements to reduce the error.
2. Voltammetry to measure the resistance of small bulbs.
1, experimental principle: according to the deformation formula of ohm's law, r = u/i.
As long as the voltage at both ends of the small bulb and the current passing through it are measured, its resistance can be calculated.
2. Experimental equipment: power supply, switch, ammeter, voltmeter, sliding rheostat, small bulb to be tested and several wires.
3. The function of sliding rheostat is to change the voltage across the measured resistor and protect the circuit.
4, experimental circuit diagram, physical diagram
5. Experimental steps
① Connect the circuit correctly according to the circuit diagram (turn off the switch and move the sliding vane of the sliding rheostat to the place with the largest resistance).
(2) After the inspection is correct, close the switch, adjust the position of the sliding vane P of the sliding rheostat, change the voltage at both ends of the resistor to U 1, U2 and U3 respectively, observe the corresponding value of the ammeter every time, and fill in the design record forms of I 1, I2 and I3 respectively:
4. When measuring the L resistance of the small bulb, measure the voltage and current values for three times and calculate the resistance value of the small bulb for three times.
However, the average value cannot be calculated, and the rated resistance under rated voltage is generally calculated.
5. The voltage of a small light bulb changes the current, the current changes the temperature, and the temperature changes the resistance.
6. The purpose of multiple measurements is to observe the change of the resistance of small bulbs with temperature under different voltages and currents.
7. The higher the temperature, the greater the resistance of the small bulb. The resistance of a small light bulb varies with temperature. )
9. What should I do if the rated voltage of the bulb is 3.8V, the power supply voltage is 6V and the voltmeter is 0 ~ 15V?
Connect a voltmeter in parallel at both ends of the sliding rheostat, and move the sliding rheostat so that the voltage of the sliding rheostat is 2.2V.