Electrical Experiment Question: What is the purpose of observing the current representation number w

Would you like to ask the answer to question (2) of this question? This question is a 10-year Dalian high school exam question, and the answer is **.

12. In the experiment of "the relationship between the brightness of the small bulb and its electric power when it is illuminated", the voltage of the power supply used is 8V, the rated voltage of the small bulb is 5V, and the maximum voltage allowed at both ends of the small bulb is times the rated voltage of the small bulb.

1) Please connect the experimental circuit in Figure 14 completely.

2) After connecting the circuit correctly, slide the sliding blade of the rheostat to the largest end of the tissue. Close the switch and find that both representations are smaller. At this time, the sliding blade of the rheostat is slowly slid towards the minimum end of the resistance value, and the two representations are observed at the same time. Then the purpose of observing the current representation is .

3) Draw the experiment**.

4) If a certain experimental voltage is selected, what is the possible impact on the experiment?

The indication of the ammeter changes with the movement of the sliding vane, the purpose of our use of the sliding rheostat is to change the current, of course, we should pay attention to the current and look at the ammeter when moving the sliding vane. There is no other phenomenon outside the sliding blade movement on the sliding rheostat, so there is no need to stare at it.

It is easy to find that the sliding rheostat is faulty if the sliding rheostat is not connected correctly, and the numbers of the voltmeter and ammeter are not looked at.

It's very extensive... To see the role of the sliding rheostat, most of the time is to see whether the range is exceeded, to prevent damage to the electrical instrument, and if the sliding rheostat is to regulate the voltage and current, you have to take the appropriate value for recording... It is necessary to analyze specific problems on a case-by-case basis.

Verify Ohm's Law!

i=u r, when the voltage is constant, the current is inversely proportional to the resistance!

From a scientific point of view, this phenomenon is a normal circuit situation, and the voltmeter and ammeter do not measure the same electrical appliance with a certain resistance.

The main reason is that the voltmeter is connected to both ends of the sliding rheostat, and the ammeter is connected to the trunk of the series circuit, which will occur when the resistance of the sliding rheostat becomes smaller.

In more detail, the resistance of the sliding rheostat decreases, the voltage division decreases, and the voltage representation number inevitably decreases.

And the total current in the line becomes larger because the total voltage does not change, and the total resistance becomes smaller, which is what Ohm's law tells us, that is, the current representation number becomes larger.

Note: At this time, the voltmeter and the ammeter are in the same circuit, and the magnitude of the indication corresponds, so it is not good to think separately from the two meters.

Sliding rheostats.

There are mainly two functions of the square cavity to pat the Yuannian surface: [protective effect and regulating effect].

with an ammeter. and voltmeter resistor" The purpose of the sliding rheostat slide in the experiment is to adjust the voltage: adjust the voltage at both ends of the measured resistor and the current provided to the measured resistor, and obtain multiple sets of corresponding voltage and current measurement values.

It is convenient to further analyze and demonstrate multiple resistance values to obtain reasonable results (conclusions).

Change the voltage across the resistor and the current through the resistor

Kid, in order to test a few more sets of data!

1. If the sliding plate resistor is moved, the resistance changes linearly continuously;

2, i=u r, the current is inversely proportional to the resistance, so the current also shows a linear continuous change;

3. The relationship between current and resistance can be reflected intuitively by using a sliding resistor.

Since the resistance of the voltmeter is much greater than the resistance of the sliding rheostat, which is equivalent to an open circuit, no matter how you slide the sliding blade, the resistance of the connected circuit is always equivalent to r+r', so the number of current representations does not change. The voltmeter measures the voltage of the right part of the sliding rheostat, when the sliding blade slides to the right, because the overall current of the circuit remains unchanged, and the resistance of the section connected to the voltmeter decreases, so the voltage representation decreases. Choose A

The ammeter remains unchanged and the voltmeter decreases. a。The voltmeter is equivalent to an open circuit, and its existence basically does not contribute to the current; The current is not changing, but the resistance measured by the voltmeter is decreasing, so its indication is decreasing.

The analysis circuit shows that the sliding rheostat is connected in parallel with the resistor, and the power supply voltage remains unchanged.

When the sliding blade p of the sliding rheostat moves to the right, the resistance of the sliding rheostat access circuit becomes larger, which is changed by i=u

r shows that the current in the sliding rheostat becomes smaller, that is, the indicator of the ammeter A2 becomes smaller;

The branches in the parallel circuit do not affect each other.

The current through the resistor R does not change, i.e. the ammeter A1

The indication of the indication is unchanged;

According to the current relationship of the parallel circuit, the trunk current is equal to the sum of the currents of each branch, so the trunk current becomes smaller, that is, the indication of ammeter A becomes smaller

So the answer is: unchanged; Becomes smaller; Becomes smaller;