Measure the resistance of the small bulb when it works 1. Experiment Name: measure the resistance of small bulb when it works 2. Voltmeter, ammeter, one small light bulb (2.5V, 3.8V), small lamp holder, four No.1 batteries and battery box, sliding rheostat (20 Ω or 50 Ω), "one" - shaped small screwdriver, switch, wire (without iron clip), pencil, ruler 3. Experimental requirements: voltammetric measurement of small bulb dark red, weak light and normal light resistance; complete the experimental report 4. Note: (1) the bulb to be tested is made by the invigilator; (2) The voltage at both ends of the bulb shall not be more than 1.2 times of the marked value 5. Draw the circuit diagram for the experiment 6. Experimental record U / V I / a R / EU 7. What is the relationship between filament resistance and filament temperature?

Measure the resistance of the small bulb when it works 1. Experiment Name: measure the resistance of small bulb when it works 2. Voltmeter, ammeter, one small light bulb (2.5V, 3.8V), small lamp holder, four No.1 batteries and battery box, sliding rheostat (20 Ω or 50 Ω), "one" - shaped small screwdriver, switch, wire (without iron clip), pencil, ruler 3. Experimental requirements: voltammetric measurement of small bulb dark red, weak light and normal light resistance; complete the experimental report 4. Note: (1) the bulb to be tested is made by the invigilator; (2) The voltage at both ends of the bulb shall not be more than 1.2 times of the marked value 5. Draw the circuit diagram for the experiment 6. Experimental record U / V I / a R / EU 7. What is the relationship between filament resistance and filament temperature?

1、 Experimental principle: P = UI
Use voltmeter to measure the voltage at both ends of the small bulb, use ammeter to measure the current in the small bulb, and use the formula P = UI to calculate the electric power. The electric power measured under the rated voltage is the rated power. This is a commonly used indirect measurement method in physics, which is also known as volt ampere method
2、 Experimental equipment
Power supply, sliding rheostat, voltmeter, ammeter, small bulb and lamp holder, switch, wire
3、 Experimental steps
1. Connect the real object according to the circuit diagram, and design the experiment record form
2. After checking the circuit, close the switch s and move the slide P of the sliding rheostat. At this time, pay attention to the indication of the voltmeter. When the indication of the voltmeter is equal to the rated voltage of the small bulb, stop sliding and record the indication of the ammeter. Substitute P = UI formula to calculate the rated power of the small bulb
3. Adjust the sliding rheostat so that the voltage at both ends of the small bulb is 1.2 times of the rated voltage, observe the light emission of the small bulb, and record the indication of the voltmeter and ammeter, and substitute it into the formula P = UI to calculate the actual power of the small bulb at this time
4. Adjust the sliding rheostat to make the voltage at both ends of the small bulb lower than the rated voltage, observe the light-emitting condition of the small bulb, record the indication of the voltmeter and ammeter, and substitute it into the formula P = UI to calculate the actual power of the small bulb at this time
5. Arrange the experimental equipment
Attention: we should pay attention to the following points in the experiment
① The power supply voltage should be higher than the rated voltage of the small bulb. For example, when measuring the electric power of the small bulb with the rated voltage of 2.5 V, at least two dry batteries should be selected as the power supply in series
② The range of voltmeter should be larger than the rated voltage of small bulb, and the range of ammeter should be larger than the normal working current of small bulb
③ The maximum current allowed by the sliding rheostat should be greater than the normal working current of the bulb, and the maximum resistance value of the sliding rheostat should be similar to that of the small bulb, so as to make the regulation effect obvious
④ According to the principle of series voltage division, the sliding rheostat should be adjusted accurately and skillfully to make the small bulb shine under three conditions: equal to the rated voltage, slightly higher than the rated voltage and lower than the rated voltage. Especially in the second experiment, the sliding rheostat should be adjusted carefully to avoid burning the bulb because the experimental voltage exceeds the rated voltage too much
⑤ When starting to connect the circuit, the switch should be disconnected. Before closing the switch, the slide of the sliding rheostat should be placed at the maximum resistance
⑥ Before the experiment, check the circuit and try to touch it. After the experiment, turn off the switch first, and then sort out the circuit

Doing the experiment of measuring the resistance of small bulb by voltammetry
① When connecting the circuit, the switch should be___________ .
② When closing the switch, check the circuit connection first, and move the slide P of the sliding rheostat to the right position___________ .
③ When a student moved the sliding rheostat after closing the switch, he found that there was no indication of ammeter and voltage sometimes. The reason may be that_________________________________ .
④ Another group of experiments found that moving slide P, the number of current indication is always zero, the light is not on, the number of voltage indication is power supply voltage, then the possible reason is that______________________ .
⑤ If the moving slide P is found, the bulb lights up and the brightness changes, the voltmeter shows the number and changes, but the ammeter does not read, the reason may be that______________________ .
⑥ If it is found that the bulb does not light up, the voltmeter does not show the number, and the ammeter shows the number and changes when the slide P is moved, the reason may be that______________________ At this time, slide p___________ (fill in "can" or "can't") to the minimum resistance
⑦ If it is found that no matter how the slide P is moved, the bulb lights up, the voltage indication is always the power supply voltage, and the ammeter has the indication and does not change, the possible reason is that_________________________________ .
⑧ If it is found that no matter how the slide P is moved, the bulb lights up, the voltmeter shows the number and remains unchanged when it is lower than the power supply voltage, and the ammeter shows the number and remains unchanged, the possible reason is that______________________ .

① When connecting the circuit, the switch should be (off)
② When closing the switch, check the circuit connection first, and move the slide P of the sliding rheostat to (the maximum resistance)
③ When a student moved the sliding rheostat after closing the switch, he found that there was no indication of ammeter and voltage sometimes. The reason may be that the resistance of sliding rheostat was too small sometimes
④ Another group of experiments found that moving slide P, the number of current indication is always zero, the lamp is not on, the number of voltage indication is power supply voltage, then the possible reason is (sliding rheostat open circuit or bulb open circuit)
⑤ If the moving slide P is found, the bulb lights up and the brightness changes, the voltmeter shows the number and changes, but the ammeter does not read, the reason may be (short circuit of the ammeter)
⑥ If it is found that when the slide P is moved, the bulb does not light, the voltmeter does not show the number, and the ammeter shows the number and changes, the reason may be that (the bulb is short circuited), at this time, the slide P (can't) (select "can" or "can't") moves to the minimum resistance position
⑦ If it is found that no matter how the slide P is moved, the bulb lights up, the voltage indication is always the power supply voltage, and the ammeter has the indication and remains unchanged, the possible cause is (short circuit of sliding rheostat)
⑧ If it is found that no matter how the slide P is moved, the bulb lights up, the voltmeter shows the number and remains unchanged when it is lower than the power supply voltage, and the ammeter shows the number and remains unchanged, the possible reason is (the sliding rheostat is connected to the following two terminals)

How to measure the resistance of a small bulb?
Measuring the resistance of small bulb by voltammetry
Is that ok?

Voltammetry should be said to be a method, principle, general formula
R=U/I

Is it right to measure electric power with electric energy meter
RTRTRTRTRTRTRTRTRTRTRTRTRTRTRTRTTRTR

If you turn off all other electrical appliances, you can directly measure the electrical appliances. Then the data measured by the electric energy meter is the electrical work of the electrical appliances

If the cosine of their angle is the root of the equation 5x2-7x-6 = 0, then the length of the other side of the triangle is ()
A. 52B. 213C. 16D. 4

By solving the equation 5x2-7x-6 = 0, the root of the equation is 2 or - 35, so the cosine of the angle cos θ = - 35. According to the cosine theorem, the length of the other side of the triangle is 32 + 52 − 2 × 3 × 5 × (− 35) = 213

All formulas for calculating electric power
It's better to have the physical formula and basic knowledge of the second volume of junior high school (for example, which zero line and fire line should be paid attention to when using the current and voltmeter), and the related classic test questions! I use them when reviewing the third grade of junior high school

A;
All circuits:
P=UI
P=W/t
Pure resistance circuit
P=I^2R
P=U^2/R
In all circuits
Q=I^2Rt