Junior Physics Resistance Problems in Circuits

There are two scenarios.

1.When there is only a sliding rheostat in the circuit, the current indication number becomes larger, and the voltage indication number does not change.

2.When there are other electrical appliances in the circuit, the current indicates that the number becomes larger, and the voltage indicates that the number becomes smaller.

Reason 1: When there is only one consumer in the circuit, the voltage at both ends of the appliance is always equal to the power supply voltage, so the voltage at both ends remains unchanged. The reason why the current indication number is higher is that the voltmeter can be determined because it is wired correctly.

The right terminal of the sliding rheostat is connected to the positive pole, so when the sliding rheostat is moved to the left, the resistance in the access circuit decreases, so the number of current representations increases.

The reason for 2 is that when the resistance of the sliding rheostat decreases, the voltage at both ends also decreases accordingly (because it is a series circuit, so there is this situation, because the voltage of the resistance in the series circuit is more, so the voltage at both ends of the sliding rheostat decreases accordingly) because the power supply voltage of the circuit remains unchanged, the voltage of other electrical appliances does not change, and the resistance of the sliding rheostat decreases, so the total resistance in the circuit decreases, and because the total power supply voltage does not change, according to Ohm's law, the current in the circuit increases.

When the slider p of the sliding rheostat slides to the left end, the resistance of the sliding rheostat to the circuit becomes smaller, so the total resistance becomes smaller and the current becomes larger.

The voltmeter, on the other hand, measures the supply voltage (if there is only a sliding rheostat in the circuit), so the voltmeter does not change.

p slides to the left end, and the sliding rheostat resistance becomes smaller.

In the whole circuit, the resistance becomes smaller, the current becomes larger, and the current representation number becomes larger; (The voltage is constant, the resistance becomes smaller, and the current becomes larger).

The sliding rheostat divides the voltage between the entire circuit (the voltage is distributed according to the size of the resistor in a series circuit).

The current indicates that the number increases, and the voltage indicates that the number increases.

Reason: When the slide moves to the left, the resistance becomes smaller, while the voltage does not change, and according to I=U r, the resistance becomes smaller and the current becomes larger.

The same goes for voltmeters.

The number of current indicators increases and the number of voltmeters decreases.

According to the Euclidean law, current = voltage resistance.

Therefore, the number of current representations decreases and the number of voltmeters increases.

Let the resistance on each side of the square be r, and the resistance between AB is equivalent to 5r 2 and 3r 2 two resistors in parallel, and the parallel circuit 1 r = 1 r1 r1 + 1 r2 gives 2 5r + 2 3r = 16 15, so r = 1

Let the wire resistance on each side of the square be r

A and B can be regarded as two resistors in parallel.

The size of the two resistors is 5 2r

3 2r, so after parallel, it is 15 16r

Equal to 15 16 ohms.

So r=1

Let the side length of the square be x, then the length of the two resistors is and respectively. And because the two resistors are connected in parallel, the sum formula of the parallel resistance is used 1 r=1 r1+1 r2, that is, 16 15=1

The x of the knot is what is sought.

Let the resistance on each side be r, and the resistance between AB is equivalent to 5r 2 and 3r 2 in parallel.

That is, r total = (5r 2) * (3r 2) [(5r 2) + (3r 2)] = 15 16

Simplification yields r=1

1. When the length is the same as the material, the resistance of the conductor decreases with the increase of the cross-sectional area; The resistance of a conductor is inversely proportional to its cross-sectional area.

Thus, all other factors being equal, the cross-sectional area is reduced by half and the resistance is doubled.

2. Resistance is the obstruction effect of the conductor on the current; It is related to the "material, length, cross-sectional area, temperature" of the conductor;

The magnitude of the resistance is directly proportional to the length of the conductor and inversely proportional to the cross-sectional area of the conductor.

Then the length change is half of the original according to the formula r=k*l s

I don't understand what you mean.

Second, the operation steps:

1. Connect the circuit according to the designed circuit diagram;

2. Close the switches S and S1, disconnect S2, and measure the voltage (U0) at both ends of the known resistance R0;

3. Close the switches S and S2, disconnect S1, measure the total voltage (U) supplied by the power supply to both ends of the series circuit;

4. Organize equipment.

3. Data analysis and processing

1. Find the current in the series circuit by i=u r: i=u0 r0;

2. R=U i is obtained from i=u r to find the resistance value of the measured resistance rx:

rx=ux/i=(u-u0)/(u0/r0)=(u-u0)r0/u0.

This is an example question in the textbook, take a good look at the book, I won't do it for you.

Circuit drawing: Rx and R are connected in series to the power supply (R is the known resistance, Rx is to be measured) because they are connected in series, so ix=IR

Use a voltmeter to measure the power supply voltage U total, r voltage ur, rx voltage uxir = ur r

ix=ir=ur/r

It can be obtained from i=u r.

rx=ux/ix=ux/(ur/r)

Connect the two resistors in series to the battery pack, measure the voltage values at both ends of the two resistors with a voltmeter, and calculate the other resistance values by using the series current equal u1 r1 = u2 r2.

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.