8th grade science resistance, 8th grade physics resistance

Analysis: Closing switch, ammeter, voltmeter have indications, because the light is very bright, indicating that the circuit resistance is small; Move.

The sliding blade of the sliding rheostat, the number of the two indicators and the brightness of the lamp are unchanged, indicating that the sliding rheostat is in the circuit.

, so the circuit fault is: the sliding rheostat is connected to the circuit by two upper wiring.

Post. Closing switches, ammeters, voltmeters have indicators, moving the slide of the sliding rheostat, and the two indicate the number and the lamp.

The brightness is unchanged, because the lamp is very dark, indicating that the circuit resistance is larger, so the circuit fault is: the sliding rheostat is connected to the circuit is two lower binding posts.

Closed switch, voltmeter has an indication, indicating that the two poles from the voltmeter to the power supply are connected; Since the ammeter has no indication, the lamp does not emit light, so the bulb is short-circuited; Then the circuit fault is: the bulb is short-circuited.

Closed switch, voltmeter has an indication, indicating that the two poles from the voltmeter to the power supply are connected; Move and slide.

Rheostat, ammeter pointer almost does not move, indicating that the circuit resistance is too large, and the sliding rheostat adjusts the circuit.

The ability of the current is too weak;

Then the circuit fault is: the voltmeter is connected in series in the circuit.

1.The rheostat is fully connected to wires.

2.The rheostat is fully connected to the resistance wire.

3.The lights are disconnected.

4.Short circuit of the rheostat.

1.It is a short circuit at both ends of the sliding rheostat.

2.The resistor of the entire sliding rheostat is connected to the circuit, and the sliding end is not connected.

3.It's the part of the circuit between the terminals of the voltmeter that is broken. If the voltmeter is connected to both ends of the bulb, then the filament is broken.

4.It should be a fault like the third question, which is open, but the connection between the ammeter and the voltmeter is different

If the closing switch, ammeter, voltmeter has an indication, the light is very bright, move the sliding rheostat, the number of both indicators and the brightness of the lamp are unchanged, what is the circuit fault?

The access resistance of the sliding rheostat is zero, that is, two upper binding posts are selected, the current is very large, and the light is very bright.

If the closing switch, ammeter, voltmeter have an indication, the lamp is dim, move the sliding rheostat, and the number of both indicators and the brightness of the lamp are unchanged, then the circuit fault is?

The slip resistance also remains the same, that is, the two lower binding posts are connected, the maximum resistance is connected, and the light is very dim.

If the switch is closed, the voltmeter has an indicator, the ammeter has no indicator, and the lamp does not emit light, what is the circuit fault?

If the ammeter has no indication, it is an open circuit, and the voltmeter is connected to a broken circuit.

If the switch is closed, the voltmeter has an indication, the sliding rheostat is moved, and the ammeter pointer barely moves, what is the circuit fault?

The sliding rheostat is short-circuited.

You are? Lu * foreign language school?

1.Something is wrong with the sliding rheostat.

2.Not enough power.

3.Short circuit. 4.There was a problem with the ammeter.

；If folded in half, the resistance becomes

The object obstructs the flow of electricity different Basically Zen-derived 300 long small Hindering ability Unchanged unchanged b a

11. Dust cavity problem: resistive 20 ohms allow the maximum current to pass through 1A D (because there is no diagram, others can't be done).

The resistance of a conductor to an electric current is called resistance and is denoted by the letter r. The SI unit of resistance is: ohm , which is denoted by the symbol .

If the voltage across the conductor is 1 V and the current passing through it is 1 A, the resistance of this conductor is 1 ohm.

2. Factors that determine the size of the resistance: the resistance of the conductor is a property of the conductor itself, and the size of the conductor resistance is determined by the material of the conductor (the conductor of different materials has different conductivity), length (the longer the conductor, the greater the resistance), the cross-sectional area (the smaller the cross-section of the conductor, the greater the resistance) and the temperature influence (for most conductors, the higher the temperature, the greater the resistance).

3. Types of resistance: Fixed-value resistance: There is a resistor with a definite resistance value, and the symbol in the circuit is .

Variable resistance: a resistance whose value can be changed within a certain range according to requirements; Slip rheostat, the symbol in the circuit is ; The resistance box can change the magnitude of the resistance value.

4. Sliding rheostat:

Function: Regulate the current in the circuit through the change of resistance.

Principle: The resistance value is changed by changing the length of the resistance wire connected in series in the circuit by the sliding arm.

Use: The binding posts on the metal rod and porcelain cylinder can only be connected up and down (i.e., "one up and down" connection), the rated power of the sliding rheostat and the maximum current allowed to pass through should be confirmed, and the resistance value should be adjusted to the maximum resistance value position before each connection to the circuit before use.

When the dicing p of the sliding rheostat is at the far right, the electrical power of the circuit is minimal.

After the switches are closed, the lamp is short-circuited, not much to say.

The total power is only 2 parts to form a scratch, and the other is the resistor R2 because of the parallel circuit. The electrical power of the resistor does not change, and the electrical power of the scratch decreases as the resistance value of the connected circuit increases, so it can be judged that the electrical power of the scratch is the smallest when the resistance value of the scratch is r1.

Divide by the formula p=square of voltage by resistance, respectively.

The sum of the two gives the total power of the circuit.

Close all the switches l and the sliding rheostat are shorted, only r2 is left to form a simple circuit, p = the square of the voltage divided by the resistance of r2, you don't give a number, how to do it, tell you the idea,

When the slip rheostat is equal to r2, the minimum total power is: 2*u*u r

"Voltammetry" is the basic method of measuring the unknown resistance, using an ammeter to measure the current i through the resistor, using a voltmeter to measure the voltage u at both ends of the resistor, and then using r=u i to calculate the resistance of the resistor. As you can see from Figure 1, this is a typical circuit diagram for "voltammetry" measurement of resistance. However, it seems too early to think that it can measure the resistance of the resistor Rx to be measured.

Because the title tells us that the resistance value of the resistor Rx is about a few hundred ohms, and the maximum supply voltage is only 3V. You can estimate the current in the circuit, which is 0.00 amps, which is roughly equivalent to the minimum graduation value of the ammeter in the diagram. In other words, it is impossible to accurately measure the current in a circuit with an ammeter.

Therefore, it is not possible to measure the resistance of a resistor in this way.

So how do you measure Rx with the equipment you already have in the question? Only on the principle of experimentation can be found. Since the ammeter does not work properly, can the Rx be measured with a voltmeter and a sliding rheostat?

Absolutely. The method is to make the resistance of the sliding rheostat zero at one time and the maximum (100W) at a time, write down the readings of the voltmeter respectively, and then calculate the resistance value of Rx by using the law in the series circuit.

You can replace the ammeter with a voltmeter or the voltmeter with an ammeter, the four types I don't know very well, but it should be two ammeters in series (two resistors in parallel), two voltmeters in parallel (two resistors in series).

That is to say, (1) first connect the position resistance RO in parallel with another fixed-value resistance RX, and then connect the RO in series with the ammeter to find the current of RO, which is recorded as IO, and then measure the current on RX in series with the ammeter, which is recorded as IX, and derive the formula: ix*rx=io*ro

rx=io/ix*ro

2) First, a galvanometer is connected in series on the trunk road, and the total current on the trunk road is measured as i, and then the current of RO and RO is recorded as IO in series with the ammeter, and the derivation formula: rx*(i-io)=io*ro, rx=io (i-io)*ro

The voltmeter is similar to that of the ammeter, first connect the voltmeter and RO in parallel to find the voltage of RO, which is recorded as UO, and then connect the voltmeter and RX in parallel to find the voltage of RX as UX, and the derivation formula: UO RO=UX RX, RX=UX UO*RO

Count the other one yourself

Well, this should be the most basic of the four types, I hope it can be used as your reference

A: 1There can be an equivalent substitution method, that is, the resistance box replaces the resistance to be measured, so that the indication of the ammeter or voltmeter is still the original value. The indication of the resistance box is sought.

2.The rest of the methods are nothing more than when using an ammeter, grasp the power supply voltage unchanged, and list the equations, such as: i1 (r to be + r to be determined) = i2r to be determined.

Solve the resistance to be measured; When using a voltmeter, grasp the current equality of the series circuit, such as: U1 (R slip + r fixed) = U2 R fixed.

The resistance value of the resistor to be measured is solved.

Current in series = (

R1 Resistance = R2=

Voltage in parallel = 10*

Current of r2 = 6 30 =

1. The resistor R1 and R2 are connected in series in the circuit, the voltage at both ends of R1 is, and the voltage at both ends of R2 is, so R2 R1=

2. If R1 and R2 are connected in parallel in another circuit, the current R1* flowing through R2

Physical Significance of Total Resistance of Parallel Circuit 1 R=1 R1+1 R2:

1.For a known circuit, the resistance values of R1 and R2 are constant. For example, two bulbs R1 and R2 are connected in parallel, their resistance is 5 ohms and 10 ohms respectively, and then they are connected in series with a battery voltage of 20 volts.

Here I can replace the above two parallel resistors with an equivalent resistor r3, so that the current in the circuit is constant. The equivalent resistance R3 here is the total resistance R, i.e., .

r3=r=r1r2 (r1+r2)=10 3 ohms, the total current in the circuit is 20 (10 3)=6 amps.

That is, in the above circuit, if I replace the two parallel bulbs R1 and R2 with an equivalent resistor R3, the total current in the circuit is 6 amps. So here the total resistance is an equivalent resistance.

2.Of course, if I replace the two bulbs, then their resistance will change, then I can still use an equivalent resistor r3 to replace the two resistors that are replaced, but the size of r3 is not the same, how small is it, can be calculated with the total resistance of the above parallel circuit 1 r = 1 r1 + 1 r2. For example, if r1=3, r2=6, r3=r=3*6 (3+6)=2 ohms.

3.The idea of equivalence is often used in physics. For example, two components can be replaced by a resultant force, and the effect is the same.

Introduce the concept of nodes.

The total resistance is the resistance between the parallel junction of two resistors.

If the sub-resistance is not specified, the resistance value is constant.

This is just a calculation formula that can be applied in different parallel circuits to calculate the total resistance of a parallel circuit. R1 and R2 represent the values of two resistors connected in parallel in a parallel circuit. So in different parallel circuits, the values of r1 and r2 are different.

The total resistance refers to the resistance after the two resistors are connected in parallel, that is, the parallel resistance of the two resistors. After connecting two resistors in parallel, the two resistors can be regarded as a whole, and the whole can be regarded as a new resistor composed of these two resistors in parallel, and the total resistance in parallel is the resistance value of the new resistor.

If there are two resistors R1 and R2 respectively, and they are connected in parallel, the total resistance is R, and R satisfies that formula.