What are the conditions for the use of R U2 p in junior high school physics?

Hello! First of all, r=u2 p is deformed from the formula p=i2r. (The two sides are multiplied by r at the same time, and the right side is given by u2 and then divided by p) and p=i2r is the power calculation formula of a pure resistance circuit, which requires that there can be no electric motors and other electrical appliances in the circuit that convert electrical energy into other non-thermal energy.

It doesn't matter whether it's connected in series or in parallel, as long as the electrical energy is not converted into other non-thermal appliances. Remember!

Due to i=u r Ohm's law.

It is only suitable for pure resistive circuits p=u2 r, and the formula that is more reversed by Ohm's law.

Therefore, it is only suitable for purely resistive circuits.

Parallel circuits, which are used in pure resistance circuits, and the resistance is constant, that is, the resistance does not change with temperature.

Parallel circuit, which is based on the parallel circuit each branch voltage equal, pure resistance or something depends on the topic.

To put it simply, in the junior high school physics stage, all electric heaters, incandescent lamps, resistors, and all formulas can be used casually, that is, it is approximate that all electrical energy is converted into internal energy.

As for electric motors and the like, they cannot be used due to Ohm's law. So the r=u2 p derived from it cannot be used either.

Used in pure resistive circuits, it is a circuit that converts all electrical energy into heat energy.

There is no motor, and the circuit that outputs work outward is about the same as the storage resistance.

The resistance is certain, but other conditions are not.

The 2 after u should be squared.

According to Ohm's theorem r=u i

i=p ur=u (p u)=(u*u) p=u p where r is the resistance, u is the voltage, and p is the power.

Ohm's law is simply described as follows: In the same circuit, the current in a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor. This law was proposed by the German physicist Georg Simon Ohm in his book "Determination of the Law of Conductivity of Metals" published in April 1826.

r: resistance.

u: Voltage. p: Power.

Resistance is equal to the square of the voltage divided by the power.

You don't need an example for this, you just need to know that these two formulas are essentially the same, only for pure resistive circuits,,, there is also a p=ui, this is a general formula, which can be used to calculate electrical power in general circuits.

There is a problem with your expression input, which should be: p i 2r and p u 2 r;

These two formulas only apply to purely resistive circuits, and for non-resistive circuits, the electrical power is calculated using the definitive P UI - it applies to all circuits.

The above two formulas are not applicable to non-pure resistive circuits such as electric motors and electric fans, and they are used to calculate the electric heating power of the resistor r.

Know the former for current and resistance to find power, and know the latter for voltage and resistance. They are all converted from the p ui.

p=ui can be used in any situation, p=u r, can be used in pure resistor, p=u2r, there is no such formula.

To know the voltage and current of the circuit, use: p=ui

To know the voltage and resistance of the circuit, use: p=u2 r

To know the current and resistance of the circuit, use: p=(i2)r

The third formula is wrong and should be p=i 2r

1) Knowing u and i finds you and r, and gets p according to p=u 2 r

This depends on the known conditions, if you know the system i,r,t, use p=i*r. For example, when the electric bai furnace is in use, the electric furnace wire.

DAO and wire in series, i electric furnace wire = i wire, the energizing time t is the same, q = i2rt, r electric furnace wire r wire, heat generated by the current:

Q electric furnace wire Q wire, so the electric furnace wire is hot and red, but the wire is almost not heated

p=i-squarer is suitable for purely resistive circuits.

This electrical power is the heating power of the circuit, which means that if there are LEDs or motors in the circuit, it cannot be counted as such. Resistor circuits are suitable.

A pure resistive circuit is the conversion of electrical energy into heat energy.

In the pure copy resistor, p=ui is obtained from Ohm's law, and p=iir=uu r is derived. In the non-pure electrical resistance, due to the conversion of electrical energy into a substance other than the internal energy, there is q

It's just to ask for power, but it's just deduced, that is, it's easy to ask for those conditions.

If you want to calculate the power of an electrical appliance, the formula p ui is applicable to all circuits. Because the formula p u r is a variant of p ui and i u r, and ohm's law is involved in this formula, it can only be used to calculate the power of electrical appliances in purely resistive circuits.

For non-electric motors, these three formulas are universal.

In a purely resistive circuit: i, u, r, p four quantities, as long as you know two of them, you can use them to find the other two. If you know u,r, use p=u2 r to find p, and p=i2r if you know i,r. It depends on the convenience.

However, in non-pure resistive circuits (such as electric motors), the only way to obtain heat is to use p=i2r.

I summed up: few students nowadays are as hard as we did when we were in junior high school, I feel that I thought deeply at that time, I remember a topic, the teacher did not make it immediately, or I came up with it myself, that was when I was in junior high school, not after: each side of the cube is a wire with a resistance value r, from any fixed point in, to another fixed point out, how many equivalent resistances are there, respectively?

If you can't do it, you can ask your teacher, and don't forget to tell me the answer: PC

This asks me hello class, I'm the class representative.

U2 R is generally used in parallel, and I2R is generally used in series, because the parallel U is equal, and the series I is equal.

p=u2／r=i2r

I2R is the work done by the current in the circuit, and it's obvious that there is i north.

Both U2 R and I2R are formulas for calculating electrical power.

U2 R is mostly used for parallel connection, and I2R is mostly used for series connection, but these two formulas cannot be used in non-pure resistance circuits such as motors, because there is internal resistance in it, which consumes a part of the electric energy, and the specific derivation formula is p=ui, u=i*r*i, i=u r

Both of these represent electrical power, the former is voltage power, the latter is current power, note that power and work are not the same concept, if you find the work done by the current, it is i2rt, where t is the time when the current does the work.

The first is the square divided by one resistance by the square of the voltage at both ends of the resistor, and the second is the square multiplied resistance of the current flowing through the resistor, both of which are only used in pure resistive circuits and can represent the work done by the current.

The first one is generally used for power in parallel circuits, because the parallel circuit voltages are equal.

The second is generally used for power in series circuits, because the current of series circuits is equal.

And both formulas only apply to purely resistive circuits.