The second year of junior high school physical resistance wire, how to learn physical resistance in

According to r=pl s there is:

1. The size of the resistance is proportional to the length. That is, the longer the length, the greater the resistance.

2. The size of the resistance is inversely proportional to the cross-sectional area. The larger the cross-sectional area, the smaller the resistance.

Therefore, the resistance in half becomes smaller, and it becomes a quarter of the original resistance. If it is folded in half, it will be reduced to a quarter, and it will become the earliest sixteenth.

The formula r l s, r is the resistance, is the resistivity, l is the length, s is the cross-sectional area, after a resistance wire is folded in half, the length is reduced by half, the cross-sectional area is doubled, the resistance is the original 1 4, and then folded in half to become the original 1 16

Smaller, because folding in half is equivalent to increasing the cross-sectional area, and at the same time reducing the length, because the larger the cross-sectional area, the smaller the resistance, and the shorter the length, the smaller the resistance, so it becomes smaller, and then folds in half is the same.

The resistance becomes smaller when folded in half.

Because folding in half increases the cross-sectional area, the larger the cross-sectional area, the smaller the resistance, so it becomes half smaller.

The longer the length, the greater the resistance, the larger the cross-sectional area, the smaller the resistance, the smaller the length after folding, the larger the cross-section, so the resistance decreases...

It gets smaller because the length l gets smaller and the section s gets bigger.

So the resistance becomes smaller.

Length l resistance = density * - cross-section s

You should know the relationship, after folding, the length becomes the original 1 2, the cross-sectional area becomes 2 times the original, the resistance becomes the original 1 4, and the resistance becomes the original 1 16

Hello!!! There are two aspects to learning resistors well.

Clause. First, the concept of resistance.

1.Resistance is a hindrance to the current.

2.Changing the resistance can change the current, but changing the current and voltage cannot change the resistance. The magnitude of the resistance is determined by the nature of the resistance itself.

3.The greater the resistivity of the material that makes up the resistor, the greater the resistance;

The longer the length of the material that makes up the resistance, the greater the resistance; Such as: sliding rheostats.

The larger the cross-sectional area (thickness) of the material that makes up the resistance, the greater the resistance;

Clause. Second, the calculation of resistance.

1.Ohm's Law. r=u/i

2.Joule's law. r=q/i2t

Just grasp the following points.

1) Resistance is the resistance of a conductor to the current, any conductor has resistance (except superconductors), but some are large and some are small.

2) The resistance of a conductor is determined by the material, length, cross-sectional area of the conductor, and is also related to temperature.

3) In general, the resistance of a conductor is considered constant.

4) The sliding rheostat is made by using the relationship between the resistance and the length of the conductor, and the rheostat must be used, and two binding posts are used when wiring.

Good luck with your studies!!

1.There are two ways to change the current in the circuit: one is to change the voltage at both ends of the circuit, which can change the number of dry batteries supplying power to the circuit or the voltage of the student power supply; The second is to change the resistance of the conductors connected in the circuit.

2.Resistance indicates the dampening effect of a conductor on an electric current. The greater the resistance of the conductor, the greater the resistance of the conductor to the current; Conversely, the smaller the resistance of a conductor, the less it has an effect on the current current.

3.Factors that determine the size of the conductor's resistance: Self factors:

The material, length, cross-sectional area of the conductor. External factors: temperature, the resistance of the metal conductor increases with the increase of temperature.

The resistance of a conductor is independent of other external factors such as voltage and current.

4.The control variable method is a commonly used research method in our experiments: when studying whether a physical quantity is related to multiple factors, the control variable method is often used.

We often change one factor and leave the others unchanged or equal, thus determining the relationship of this factor to the physical quantity being studied. The factors involved are judged one by one, and finally comprehensively resolved. For example, when studying the relationship between the magnitude and length of the conductor's resistance, it is necessary to control the material, cross-sectional area, and temperature to be the same or unchanged, change the length of the conductor, and observe the current change to judge the relationship between the resistance and the length of the conductor.

1.Answer: (1) Method: Use a wire to connect the waste bulb wick and the power switch ammeter into a diagram circuit, and then heat the wick with alcohol, etc., and observe the change of the current representation at the same time, and analyze it to draw conclusions. (2) The circuit is shown in the figure.

2.Solution: As you can see from the figure, L1L2 is connected in parallel, because the voltmeter range is 15V, and the pointer is one large grid and two small squares, then U=U1=U2=6V

A1 measures the total current A2 is the L1 current, I total = i1 + i2 from the question to know the current of i total = i1 = l2 i2 = i total - i1 = — =

Answer: The power supply voltage, the voltage at both ends of L1 and L2 is 6V, and the current through L1 and L2 is , respectively.

1) The voltage at both ends of L1 and L2 is equal to the power supply voltage (the voltage at both ends of the parallel circuit is equal);

2) Since the readings of the two ammeters are the same, the current on L1 is equal to the ammeter reading, while L2 is not on (the total current is equal to the sum of the currents of each circuit);

These two are related, in the case of a single conductor, the heat energy is equal to the voltage multiplied by the current (p=ui), and it is also equal to the square of the voltage divided by the resistance (p=uu r), comparing the two formulas to understand that the voltage is equal to the current multiplied by the resistance (u=ir), so these formulas can be deduced from each other.

When the quality of the resistance is the problem, the specific problem depends on the voltage or current in the specific situation, and then use the above formula to see the relationship between resistance and energy, and then judge the quality of the resistance.

As for what resistance is, you look at the definition, it is an obstacle to the current, but in the process of hindering, part of the electrical energy is turned into thermal energy.

The essence of resistance is how much can be converted into other forms" is not true, when the voltage is constant, the conversion heat energy is inversely proportional to the resistance, and when the current is constant, the conversion heat energy is proportional to the resistance. In addition, the amount of winter candied fruit that can be reduced to iodine irrigation is not only thermal energy, but also mechanical energy when you learn the motor, so the relationship is even more complicated, not just positive and inverse proportional relationships. You can't just say what is, the relationship between physical quantities is conditional, everything is subject to the formula, and the other quantities in the formula are fixed in order to say what kind of relationship one quantity has with another.

The diameter is 1 N, and the radius is 1 N. The resistivity of the resistance wire does not change, and the volume v does not change.

Three-step solution: the cross-sectional area of the original resistance wire is s1 = r1 squared, the length is l1, the volume v1 = s1l1, and the resistivity is .

Later, the cross-sectional area of the resistance wire is s2=

r-squared = (1 n)r1 squared = s1

1 n) square, the length is l2, the resistivity is , the volume v2 = s2l2, and later the length of the resistance wire l2 = v2 s2 = s1l1 s1 (1 n) square = l1 n squared.

According to r= l s, get.

The ratio of the later resistance to the original resistance.

r2/r1=(ρl2/s2)/(ρl1/s1)=s1l2/(s2l1)

s1 (l1 n squared) s1

1 n) square l1

n to the 4th power.

r2=n to the power of 4 r1

Answer: The current resistance is 4 times the original n.

The larger the cross-section, the smaller the resistance, the more electrons pass through the cross-section at the same time, the greater the current;

The longer the length, the greater the resistance, and the more the electrical energy is converted into a magnetic field force.

Because A resistance is a variable resistance, with the change of voltage, the resistance value of A will also increase correspondingly, and B has a certain value of resistance.

If the branch resistance increases, then the total resistance increases.

So choose D

The slope of the image is resistive. B does not change, A decreases with the increase of current. The sum of the reciprocal of the resistors after parallel connection is the reciprocal of the total resistance. The reciprocal of B remains the same, and the reciprocal of A becomes larger, so the total resistance decreases.