Ampere magnetic force. How to convert amps to watts and vice versa?

Ampere's law

Ampere's force is the main component of Ampere's law - the law on the interaction of electric currents.
It states that in parallel conductors, in which electric currents flow in the same direction, an attractive force arises. And in those conductors in which electric currents flow in opposite directions, a repulsive force arises. Also called Ampere's law is a law that determines the strength of a magnetic field in a small part of a conductor through which current flows. In this case, it is defined as the result of multiplying the current density that flows through the conductor by the induction of the magnetic field in which the conductor is located. From Ampere's law itself, it is concluded that Ampere's force is equal to zero if the angle located between the current and the magnetic induction line is also equal to zero. In other words, the conductor must be located along the magnetic induction line to achieve zero value.

Ampere's Law - Definition

Andre Ampère in 1920 defined the force with which a magnetic field affects a conductor placed in it. He established a direct relationship between the force arising around the conductor, the strength of the current, the magnitude of magnetic induction and the sine of the angle between the magnetic induction vector and the direction of the current.

The expression looks like:

FA = B *I*L*sinα,

Where:

• FA – Ampere force, N;
• B – magnetic induction module;
• I – current strength, A;
• L – length of the conductor section, m.

The definition is valid for a conductor along which there is a constantly directed movement of electrons.

What is Ampere power

Actually, the ampere force is the force of the magnetic field on the conductor through which the current flows. The Ampere force is calculated by the formula as the result of multiplying the current density passing through the conductor by the induction of the magnetic field in which the conductor is located. As a result, the Ampere force formula will look like this

sa=st*dchp*mi

Where, sa is the Ampere force, st is the current strength, dchp is the length of the conductor part, mi is the magnetic induction.

Ampere's Force, Ampere's Law, Left Hand Rule:

• Ampere force: is the force acting on a current-carrying conductor placed in a magnetic field
• Rule of the left hand: if the left hand is positioned so that the component of vector B perpendicular to the conductor enters the palm, and four extended fingers are directed in the direction of current movement, then the thumb warmed to 90° will show the direction of the force acting on the section of the conductor

Lorentz force direction

We have already mentioned that the direction of the resulting Lorentz force, in addition to magnetic parameters, is determined (including) by the polarity of the charge. If we had the opportunity to observe a charged elementary particle located in a magnetic field, then from the vector of its movement we could determine the direction of the force vector F.

But in practice, it is very difficult to observe elementary charges due to their tiny sizes. Therefore, to determine this direction, a method is used, known as the left-hand rule (Fig. 4).

Rice. 4. Finding the Lorentz force vector

The palm must be turned so that the induction vector enters it. In the case of a positive charge, the extended fingers are positioned according to the movement of the particle. (for a negative charge, fingers point in the opposite direction). The thumb points at a right angle to the desired direction.

If the orientation of the particle velocity vector is known, then the directions of the remaining vectors can be determined by applying the right-hand rule, which is clear from Figure 5.

Rice. 5. Example of application of the right hand rule

Ampere strength (using two parallel conductors)

Imagine two infinite conductors that are located at a certain distance.
Currents flow through them. If currents flow in one direction, then the conductors attract. Otherwise, they will repel each other. The fields that parallel conductors create are directed counter to each other. And to understand why they react this way, you just need to remember that like poles of magnets or like charges always repel. To determine the directional side of the field created by the conductor, the right-hand screw rule should be used.

Power units

Converting watts to amperes and vice versa is a relative concept, because these are different units of measurement. Amps are a physical quantity of electric current, that is, the speed at which electricity flows through a cable. Watt is the amount of electrical power, or the rate of electricity consumption. But such a translation is necessary in order to calculate whether the value of the current corresponds to the value of its power.

Relationship with other SI units

What amperes are from the point of view of the connection between electrical units can be seen in the following examples:

• at a current of 1 ampere (A), the cross-section of the conductor passes through itself a charge of 1 coulomb (C) in one second;
• when a charge of 1 ampere is applied to the plates of a capacitor with a capacity of 1 F, the voltage on the plates will increase, increasing by 1 V every second;
• the capacity of galvanic sources and batteries is measured in ampere-hours (A*h, or A*h), 1 A*h = 3660 C, this amount of electricity flows through the conductor in 1 hour;
• the maximum output power (watt) of rectifiers or power supplies is the second most important characteristic of such sources and is marked V*A;
• the amount of electricity in a lightning discharge is approximately 500 kiloamperes (1 kA = 10³ A);
• a 0.1 kilowatt (kW) incandescent light bulb consumes 0.5 A.

The designation of the number of amperes is applied to the housings of circuit breakers and fuses.

Converting amperes to watts and kilowatts

Knowing how to calculate the correspondence between amperes and watts is necessary in order to determine which device can withstand the power of connected consumers. Such devices include protective equipment or switching equipment.

Before choosing which circuit breaker or residual current device (RCD) to install, you need to calculate the power consumption of all connected devices (iron, lamps, washing machine, computer, etc.). Or, on the contrary, knowing the cost of a circuit breaker or protective shutdown device, determine which equipment will withstand the load and which will not.

To convert amperes to kilowatts and vice versa, there is a formula: I=P/U, where I are amperes, P are watts, U are volts. Volts are the mains voltage. In residential premises, a single-phase network is used - 220 V. In production, to connect industrial equipment, a three-phase electrical network is used, the value of which is 380 V. Based on this formula, knowing the amperes, you can calculate the correspondence to watts and vice versa - convert watts to amperes.

Situation: There is a circuit breaker. Technical parameters: rated current 25 A, 1-pole. You need to calculate what wattage of devices the machine can withstand.

The easiest way is to enter technical data into a calculator and calculate the power. You can also use the formula I=P/U, it will turn out: 25 A=x W/220 V.

x W=5500 W.

To convert watts to kilowatts, you need to know the following measures of power in watts:

• 1000 W = 1 kW,
• 1000 000 W = 1000 kW = MW,
• 1000,000,000 W = 1,000 MW = 1,000,000 kW, etc.

This means 5500 W = 5.5 kW. Answer: a machine with a rated current of 25 A can withstand the load of all devices with a total power of 5.5 kW, no more.

Apply a formula with voltage and current data in order to select the type of cable based on power and current. The table shows the current correspondence to the wire cross-section:

Copper cores of wires and cablesCode cross-section, mm²Copper cores of wires, cables

How to convert watt to ampere

You need to convert watts to amperes in a situation where you need to install a protective device and you need to choose what rated current it should have. It is clear from the operating instructions how many watts a household appliance connected to a single-phase network consumes.

The task is to calculate how many amperes in watts or what kind of socket to connect to if the microwave oven consumes 1.5 kW. For ease of calculation, it is better to convert kilowatts into watts: 1.5 kW = 1500 W. We substitute the values ​​into the formula and get: 1500 W / 220 V = 6.81 A. We round the values ​​up and get 1500 W in terms of amperes - microwave current consumption is at least 7 A.

If you connect several devices simultaneously to one protection device, then in order to calculate how many amperes there are in watts, you need to add all the consumption values ​​together. For example, the room uses lighting with 10 pcs LED lamps. 6 W, iron 2 kW and TV 30 W. First, all indicators need to be converted into watts, it turns out:

• lamps 6*10= 60 W,
• iron 2 kW=2000 W,
• TV 30 W.

60+2000+30=2090 W.

Now you can convert amperes to watts, to do this we substitute the values ​​in the formula 2090/220 V = 9.5 A ~ 10 A. Answer: current consumption is about 10 A.

You need to know how to convert amps to watts without a calculator. The table shows the correspondence between the rate of electricity consumption and the current strength for single-phase and three-phase networks.

Application of Ampere force

The use of Ampere's force in the modern world is very wide; one can even say without exaggeration that we are literally surrounded by the power of Ampere. For example, when you are riding in a tram, trolleybus, or electric car, it is this force, the Ampere force, that sets it in motion. Elevators, electric gates, doors, any electrical appliances are similar; all this works precisely thanks to the power of Ampere.

Experiment

In order to be able to see with your own eyes the effect of the Ampere force, you can conduct a small experiment at home.
First you need to take a horseshoe magnet in which a conductor is placed between the poles. It is advisable to reproduce everything as in the picture. If you close the key, you can see that the conductor will begin to move, shifting from the initial equilibrium point. You can experiment with the directions of current passage and see that depending on the direction of movement, the direction of deflection of the conductor changes. From the experiment itself, several observations can be made that confirm the above:

• The magnetic field acts exclusively on the current-carrying conductor.
• A conductor carrying current in a magnetic field is acted upon by a force that is a consequence of their interaction. It is under the influence of this force that the conductor moves in space within the boundaries of the magnetic field.
• The nature of the interaction directly depends on the voltage of the electric current and the magnetic field lines.
• The field does not act on a current-carrying conductor if the current in the conductor flows parallel to the direction of the field lines.

Application of Lorentz force in technology

Kinescope

The kinescope, which was installed until recently, when it was replaced by an LCD (flat) screen, in every TV, would not have been able to work without the Lorentz force. To form a television raster from a narrow stream of electrons on the television screen, deflection coils are used, in which a linearly varying magnetic field is created. Line coils move the electron beam from left to right and return it back; frame coils are responsible for vertical movement, moving the beam running horizontally from top to bottom. The same principle is used in oscilloscopes - devices used to study alternating electrical voltage.

Mass spectrograph

A mass spectrograph is a device that uses the dependence of the radius of rotation of a charged particle on its specific charge. The principle of its operation is as follows:

A source of charged particles that gain speed using an artificially created electric field is placed in a vacuum chamber in order to eliminate the influence of air molecules. The particles fly out from the source and, having passed along a circular arc, hit the photographic plate, leaving marks on it. Depending on the specific charge, the radius of the trajectory and, therefore, the point of impact changes. This radius is easy to measure, and knowing it, you can calculate the mass of the particle. Using a mass spectrograph, for example, the composition of lunar soil was studied.

Test tasks on the topic: magnetic interaction of currents and Ampere force

Problem 1. Prove that two parallel conductors carrying currents in the same direction attract each other.

Task analysis:

There is a magnetic field around any conductor carrying current, therefore, each of the two conductors is in the magnetic field of the other. The first conductor is acted upon by an Ampere force from the magnetic field created by the current in the second conductor, and vice versa. Having determined the directions of these forces using the left-hand rule, we will find out how the conductors behave.

Solution:

During the solution, we will make explanatory drawings: we will depict conductors A and B, show the direction of the current in them, etc.

Let us determine the direction of the Ampere force acting on conductor A located in the magnetic field of conductor B.

1) Using the gimlet rule, we determine the direction of the magnetic induction lines of the magnetic field created by conductor B (figure on the left). It turns out that conductor A has magnetic lines directed towards us (o).

2) Using the left-hand rule, we determine the direction of the Ampere force acting on conductor A from the magnetic field of conductor B.

3) We come to the conclusion: conductor A is attracted to conductor B.

Now let's find the direction of the Ampere force acting on conductor B, which is in the magnetic field of conductor A.

1) Determine the direction of the magnetic induction lines of the magnetic field created by conductor A (figure on the right). It turns out that conductor B has magnetic lines directed away from us (o).

2) Determine the direction of the Ampere force acting on conductor B.

3) We come to the conclusion: conductor B is attracted to conductor A.

Answer: two parallel conductors carrying currents in the same direction actually attract each other.

Problem 2. A straight conductor (rod) 0.1 m long and weighing 40 g is in a horizontal uniform magnetic field with an induction of 0.5 Tesla. The rod is located perpendicular to the magnetic field lines). What current strength and in what direction should be passed through the rod so that it does not put pressure on the support (hangs in a magnetic field)?

Task analysis:

The rod will not press on the support if the Ampere force balances the force of gravity. This will happen under the following conditions:

1. Ampere's force will be directed opposite to gravity (that is, vertically upward)
2. the value of Ampere's force is equal to the value of gravity FA = Fgrav

We determine the direction of the current using the left-hand rule.

Solution:

Let's determine the direction of the current. To do this, position your left hand so that the magnetic field lines enter the palm, and the thumb bent 90° is directed vertically upward. Four outstretched fingers will indicate the direction away from us. So, the current in the conductor should be directed away from us.

We take into account that FA = F heavy. FA= BIlsinα, where sin α = 1; Fstrand = mg

From the last expression we find the current strength: I = mg/Bl

Let's check the unit and find the value of the desired quantity.

Answer: I = 8 A; The current is in the direction away from us.

Let's sum it up

The force with which a magnetic field acts on a current-carrying conductor is called the Ampere force. The value of the Ampere force is calculated by the formula: FA = BIlsinα, where B is the magnetic field induction; I is the current strength in the conductor; l is the length of the active part of the conductor; α is the angle between the direction of the magnetic induction vector and the direction of the current in the conductor.

To determine the direction of Ampere's magnetic force, the left hand rule is used: if the left hand is positioned so that the magnetic field lines enter the palm, and four extended fingers indicate the direction of the current in the conductor, then the thumb bent 90 ° will indicate the direction of the Ampere force.

Types of electromagnetic forces

Definition 1

Electromagnetic forces are forces that act between bodies due to the fact that these bodies consist of charged moving particles between which magnetic and electric forces act.

Electromagnetic forces include:

• friction force $ \vec{ F_{tr}} $;
• elastic force $ \vec{ F_{control}} $;
• body weight $ \vec{ P} $.

Definition 2

The friction force $ \vec{ F_{tr}} $ is an electromagnetic force that arises due to the fact that the contacting bodies have uneven surfaces.

The friction force is always directed in the direction opposite to the movement. It has no application point. There are two types of friction force:

1. Static friction force. It occurs when the bodies are at relative rest, in other words, when the bodies in contact are absolutely motionless relative to each other. The static friction force is always equal in magnitude to the external force and is directed in the opposite direction. It cannot exceed the maximum value $F_{tr.\max} = \mu N$.
2. If the external force applied to the body becomes greater than $F_{tr.\max}$, then slipping occurs. The friction force in this case is called “sliding friction force”.

The sliding friction force is determined by the following formula:

$F_{tr.} = \mu N$, where

• $ \mu $ is the friction coefficient (dimensionless quantity), which depends only on the material of manufacture of the bodies and the degree of their processing;
• $N$ is the ground reaction force.

In addition to the above friction forces, one can also distinguish electromagnetic forces of viscous friction and rolling friction forces.

Definition 3

The elastic force $ \vec{ F_{exerc}} $ is an electromagnetic force that occurs during elastic deformation in a body.

It is directed opposite to the deformation. The modulus of elastic force can be calculated using the formula:

$ |F_{control}| = k \delta l$, where

• $k$ is the spring stiffness;
• $\delta l$ is the deformation.

Electromagnetic forces also include body weight.

Definition 4

The weight of a body $ \vec{ P} $ is the electromagnetic force with which a body acts on other bodies due to its attraction to the surface of the Earth.

If a body is at rest relative to the vertical or moves up or down uniformly, then its weight is equal to the force of gravity:

$P = mg$

If a body moves up with deceleration or down with acceleration, then its weight is significantly less than the force of gravity. You can find it using the following formula:

$P= m(ga)$

If a body falls freely, then a weightless state occurs. In this case, body weight is equal to zero:

$P = 0$

If a body goes down with deceleration or moves up with acceleration, then its weight exceeds the force of gravity. You can find body weight using the formula:

$P = m(g + a)$

In this case, the ratio of body weight to gravity can be called overload.

The formula for the weight of a body that moves uniformly accelerated through a vector difference can generally be expressed as follows:

$\vec{P} = m(\vec{g} -\vec{a})$