Electric current is generated in order to be used in the future for certain purposes, to perform some kind of work. Thanks to electricity, all devices, devices and equipment function. The work itself represents a certain effort applied to move an electric charge over a set distance. Conventionally, such work within a section of the circuit will be equal to the numerical value of the voltage in this section.
To perform the necessary calculations, you need to know how the work of the current is measured. All calculations are carried out on the basis of initial data obtained using measuring instruments. The larger the charge, the more effort is required to move it, and the more work will be done.
What is the work of current called?
Electric current, as a physical quantity, in itself has no practical significance. The most important factor is the effect of the current, characterized by the work it performs. The work itself represents certain actions during which one type of energy is transformed into another. For example, electrical energy is converted into mechanical energy by rotating the motor shaft. The work of electric current itself is the movement of charges in a conductor under the influence of an electric field. In fact, all the work of moving charged particles is done by the electric field.
In order to perform calculations, a formula for the operation of electric current must be derived. To compile formulas, you will need parameters such as current strength and. Since the work done by an electric current and the work done by an electric field are the same thing, it will be expressed as the product of the voltage and the charge flowing in the conductor. That is: A = Uq. This formula was derived from the relationship that determines the voltage in the conductor: U = A/q. It follows that voltage represents the work done by the electric field A to transport a charged particle q.
The charged particle or charge itself is displayed as the product of the current strength and the time spent on the movement of this charge along the conductor: q = It. In this formula, the relation for the current strength in the conductor was used: I = q/t. That is, it is the ratio of the charge to the period of time during which the charge passes through the cross section of the conductor. In its final form, the formula for the work of electric current will look like the product of known quantities: A = UIt.
In what units is the work of electric current measured?
Before directly addressing the question of how the work of electric current is measured, it is necessary to collect the units of measurement of all physical quantities with which this parameter is calculated. Any work, therefore, the unit of measurement of this quantity will be 1 Joule (1 J). Voltage is measured in volts, current is measured in amperes, and time is measured in seconds. This means the unit of measurement will look like this: 1 J = 1V x 1A x 1s.
Based on the obtained units of measurement, the work of electric current will be determined as the product of the current strength in a section of the circuit, the voltage at the ends of the section and the period of time during which the current flows through the conductor.
Measurements are carried out using a voltmeter and a clock. These devices allow you to effectively solve the problem of how to find the exact value of a given parameter. When connecting an ammeter and a voltmeter to a circuit, it is necessary to monitor their readings for a specified period of time. The obtained data is inserted into the formula, after which the final result is displayed.
The functions of all three devices are combined in electric meters that take into account the energy consumed, and in fact the work done by electric current. Here another unit is used - 1 kW x h, which also means how much work was done during a unit of time.
In everyday life we often come across such a concept as work. What does this word mean in physics and how to determine the work of the elastic force? You will find out the answers to these questions in the article.
Mechanical work
Work is a scalar algebraic quantity that characterizes the relationship between force and displacement. If the direction of these two variables coincides, it is calculated using the following formula:
- F- module of the force vector that does the work;
- S- displacement vector module.
A force that acts on a body does not always do work. For example, the work done by gravity is zero if its direction is perpendicular to the movement of the body.
If the force vector forms a non-zero angle with the displacement vector, then another formula should be used to determine the work:
A=FScosα
α - the angle between the force and displacement vectors.
Means, mechanical work is the product of the projection of force on the direction of displacement and the module of displacement, or the product of the projection of displacement on the direction of force and the module of this force.
Mechanical work sign
Depending on the direction of the force relative to the movement of the body, the work A can be:
- positive (0°≤ α<90°);
- negative (90°<α≤180°);
- equal to zero (α=90°).
If A>0, then the speed of the body increases. An example is an apple falling from a tree to the ground. At A<0 сила препятствует ускорению тела. Например, действие силы трения скольжения.
The SI (International System of Units) unit of work is Joule (1N*1m=J). A joule is the work done by a force, the value of which is 1 Newton, when a body moves 1 meter in the direction of the force.
Work of elastic force
The work of force can also be determined graphically. To do this, calculate the area of the curvilinear figure under the graph F s (x).
Thus, from the graph of the dependence of the elastic force on the elongation of the spring, one can derive the formula for the work of the elastic force.
It is equal to:
A=kx 2 /2
- k- rigidity;
- x- absolute elongation.
What have we learned?
Mechanical work is performed when a force is applied to a body, which leads to movement of the body. Depending on the angle that occurs between the force and the displacement, the work can be zero or have a negative or positive sign. Using the example of elastic force, you learned about a graphical method for determining work.
Before revealing the topic “How work is measured,” it is necessary to make a small digression. Everything in this world obeys the laws of physics. Each process or phenomenon can be explained on the basis of certain laws of physics. For each measured quantity there is a unit in which it is usually measured. Units of measurement are constant and have the same meaning throughout the world.
Jpg?.jpg 600w, https://elquanta.ru/wp-content/uploads/2018/03/risunok-1-768x451..jpg 1024w" sizes="(max-width: 600px) 100vw, 600px">
System of international units
The reason for this is the following. In nineteen sixty, at the Eleventh General Conference on Weights and Measures, a system of measurements was adopted that is recognized throughout the world. This system was named Le Système International d’Unités, SI (SI System International). This system has become the basis for determining units of measurement accepted throughout the world and their relationships.
Physical terms and terminology
In physics, the unit of measurement of the work of force is called J (Joule), in honor of the English physicist James Joule, who made a great contribution to the development of the branch of thermodynamics in physics. One Joule is equal to the work done by a force of one N (Newton) when its application moves one M (meter) in the direction of the force. One N (Newton) is equal to a force of one kg (kilogram) mass with an acceleration of one m/s2 (meter per second) in the direction of the force.
Jpg?.jpg 600w, https://elquanta.ru/wp-content/uploads/2018/03/risunok-2-2-210x140.jpg 210w" sizes="(max-width: 600px) 100vw, 600px">
Formula for finding a job
For your information. In physics, everything is interconnected; performing any work involves performing additional actions. As an example, we can take a household fan. When the fan is plugged in, the fan blades begin to rotate. The rotating blades influence the air flow, giving it directional movement. This is the result of the work. But to perform the work, the influence of other external forces is necessary, without which the action is impossible. These include electric current, power, voltage and many other related values.
Electric current, at its core, is the ordered movement of electrons in a conductor per unit time. Electric current is based on positively or negatively charged particles. They are called electric charges. Denoted by the letters C, q, Kl (Coulomb), named after the French scientist and inventor Charles Coulomb. In the SI system, it is a unit of measurement for the number of charged electrons. 1 C is equal to the volume of charged particles flowing through the cross section of a conductor per unit time. The unit of time is one second. The formula for electric charge is shown in the figure below.
Jpg?.jpg 600w, https://elquanta.ru/wp-content/uploads/2018/03/risunok-3-768x486..jpg 848w" sizes="(max-width: 600px) 100vw, 600px">
Formula for finding electric charge
The strength of electric current is indicated by the letter A (ampere). Ampere is a unit in physics that characterizes the measurement of the work of force that is expended to move charges along a conductor. At its core, electric current is the ordered movement of electrons in a conductor under the influence of an electromagnetic field. A conductor is a material or molten salt (electrolyte) that has little resistance to the passage of electrons. The strength of electric current is affected by two physical quantities: voltage and resistance. They will be discussed below. Current strength is always directly proportional to voltage and inversely proportional to resistance.
Jpg?.jpg 600w, https://elquanta.ru/wp-content/uploads/2018/03/risunok-4-768x552..jpg 800w" sizes="(max-width: 600px) 100vw, 600px">
Formula for finding current strength
As mentioned above, electric current is the ordered movement of electrons in a conductor. But there is one caveat: they need a certain impact to move. This effect is created by creating a potential difference. Electric charge can be positive or negative. Positive charges always tend towards negative charges. This is necessary for the balance of the system. The difference between the number of positively and negatively charged particles is called electrical voltage.
Gif?.gif 600w, https://elquanta.ru/wp-content/uploads/2018/03/risunok-5-768x499.gif 768w" sizes="(max-width: 600px) 100vw, 600px">
Formula for finding voltage
Power is the amount of energy expended to do one J (Joule) of work in a period of time of one second. The unit of measurement in physics is designated as W (Watt), in the SI system W (Watt). Since electrical power is considered, here it is the value of the electrical energy expended to perform a certain action in a period of time.
Jpg?.jpg 600w, https://elquanta.ru/wp-content/uploads/2018/03/risunok-6-120x74..jpg 750w" sizes="(max-width: 600px) 100vw, 600px">
Formula for finding electrical power
In conclusion, it should be noted that the unit of measurement of work is a scalar quantity, has a relationship with all branches of physics and can be considered from the perspective of not only electrodynamics or thermal engineering, but also other sections. The article briefly examines the value characterizing the unit of measurement of the work of force.
Video
« Physics - 10th grade"
The law of conservation of energy is a fundamental law of nature that allows us to describe most occurring phenomena.
Description of the movement of bodies is also possible using such concepts of dynamics as work and energy.
Remember what work and power are in physics.
Do these concepts coincide with everyday ideas about them?
All our daily actions come down to the fact that we, with the help of muscles, either set the surrounding bodies in motion and maintain this movement, or stop the moving bodies.
These bodies are tools (hammer, pen, saw), in games - balls, pucks, chess pieces. In production and agriculture, people also set tools in motion.
The use of machines increases labor productivity many times due to the use of engines in them.
The purpose of any engine is to set bodies in motion and maintain this movement, despite braking by both ordinary friction and “working” resistance (the cutter should not just slide along the metal, but, cutting into it, remove chips; the plow should loosen land, etc.). In this case, a force must act on the moving body from the side of the engine.
Work is performed in nature whenever a force (or several forces) from another body (other bodies) acts on a body in the direction of its movement or against it.
The force of gravity does work when raindrops or stones fall from a cliff. At the same time, work is also done by the resistance force acting on the falling drops or on the stone from the air. The elastic force also performs work when a tree bent by the wind straightens.
Definition of work.
Newton's second law in impulse form Δ = Δt allows you to determine how the speed of a body changes in magnitude and direction if a force acts on it during a time Δt.
The influence of forces on bodies that lead to a change in the modulus of their velocity is characterized by a value that depends on both the forces and the movements of the bodies. In mechanics this quantity is called work of force.
A change in speed in absolute value is possible only in the case when the projection of the force F r on the direction of movement of the body is different from zero. It is this projection that determines the action of the force that changes the velocity of the body modulo. She does the work. Therefore, work can be considered as the product of the projection of force F r by the displacement modulus |Δ| (Fig. 5.1):
A = F r |Δ|. (5.1)
If the angle between force and displacement is denoted by α, then Fr = Fcosα.
Therefore, the work is equal to:
A = |Δ|cosα. (5.2)
Our everyday idea of work differs from the definition of work in physics. You are holding a heavy suitcase, and it seems to you that you are doing work. However, from a physical point of view, your work is zero.
The work of a constant force is equal to the product of the moduli of the force and the displacement of the point of application of the force and the cosine of the angle between them.
In the general case, when a rigid body moves, the displacements of its different points are different, but when determining the work of a force, we are under Δ we understand the movement of its point of application. During the translational motion of a rigid body, the movement of all its points coincides with the movement of the point of application of the force.
Work, unlike force and displacement, is not a vector, but a scalar quantity. It can be positive, negative or zero.
The sign of the work is determined by the sign of the cosine of the angle between force and displacement. If α< 90°, то А >0, since the cosine of acute angles is positive. For α > 90°, the work is negative, since the cosine of obtuse angles is negative. At α = 90° (force perpendicular to displacement) no work is done.
If several forces act on a body, then the projection of the resultant force on the displacement is equal to the sum of the projections of the individual forces:
F r = F 1r + F 2r + ... .
Therefore, for the work of the resultant force we obtain
A = F 1r |Δ| + F 2r |Δ| + ... = A 1 + A 2 + .... (5.3)
If several forces act on a body, then the total work (the algebraic sum of the work of all forces) is equal to the work of the resultant force.
The work done by a force can be represented graphically. Let us explain this by depicting in the figure the dependence of the projection of force on the coordinates of the body when it moves in a straight line.
Let the body move along the OX axis (Fig. 5.2), then
Fcosα = F x , |Δ| = Δ x.
For the work of force we get
A = F|Δ|cosα = F x Δx.
Obviously, the area of the rectangle shaded in Figure (5.3, a) is numerically equal to the work done when moving a body from a point with coordinate x1 to a point with coordinate x2.
Formula (5.1) is valid in the case when the projection of the force onto the displacement is constant. In the case of a curvilinear trajectory, constant or variable force, we divide the trajectory into small segments, which can be considered rectilinear, and the projection of the force at a small displacement Δ - constant.
Then, calculating the work on each movement Δ
and then summing up these works, we determine the work of the force on the final displacement (Fig. 5.3, b). Unit of work.
The unit of work can be established using the basic formula (5.2). If, when moving a body per unit length, it is acted upon by a force whose modulus is equal to one, and the direction of the force coincides with the direction of movement of its point of application (α = 0), then the work will be equal to one. In the International System (SI), the unit of work is the joule (denoted by J):
1 J = 1 N 1 m = 1 N m.
Joule- this is the work done by a force of 1 N on displacement 1 if the directions of force and displacement coincide.
Multiple units of work are often used: kilojoule and megajoule:
1 kJ = 1000 J,
1 MJ = 1000000 J.
Work can be completed either in a large period of time or in a very short one. In practice, however, it is far from indifferent whether work can be done quickly or slowly. The time during which work is performed determines the performance of any engine. A tiny electric motor can do a lot of work, but it will take a lot of time. Therefore, along with work, a quantity is introduced that characterizes the speed with which it is produced - power.
Power is the ratio of work A to the time interval Δt during which this work is done, i.e. power is the speed of work:
Substituting into formula (5.4) instead of work A its expression (5.2), we obtain
Thus, if the force and speed of a body are constant, then the power is equal to the product of the magnitude of the force vector by the magnitude of the velocity vector and the cosine of the angle between the directions of these vectors. If these quantities are variable, then using formula (5.4) one can determine the average power in a similar way to determining the average speed of a body.
The concept of power is introduced to evaluate the work per unit of time performed by any mechanism (pump, crane, machine motor, etc.). Therefore, in formulas (5.4) and (5.5), traction force is always meant.
In SI, power is expressed in watts (W).
Power is equal to 1 W if work equal to 1 J is performed in 1 s.
Along with the watt, larger (multiple) units of power are used:
1 kW (kilowatt) = 1000 W,
1 MW (megawatt) = 1,000,000 W.
Every body that makes a movement can be characterized by work. In other words, it characterizes the action of forces.
Work is defined as:
The product of the modulus of force and the path traveled by the body, multiplied by the cosine of the angle between the direction of force and movement.
Work is measured in Joules:
1 [J] = = [kg* m2/s2]
For example, body A, under the influence of a force of 5 N, traveled 10 m. Determine the work done by the body.
Since the direction of movement and the action of the force coincide, the angle between the force vector and the displacement vector will be equal to 0°. The formula will be simplified because the cosine of an angle of 0° is equal to 1.
Substituting the initial parameters into the formula, we find:
A= 15 J.
Let's consider another example: a body weighing 2 kg, moving with an acceleration of 6 m/s2, has traveled 10 m. Determine the work done by the body if it moved upward along an inclined plane at an angle of 60°.
To begin with, let's calculate how much force needs to be applied to impart an acceleration of 6 m/s2 to the body.
F = 2 kg * 6 m/s2 = 12 H.
Under the influence of a force of 12N, the body moved 10 m. The work can be calculated using the already known formula:
Where, a is equal to 30°. Substituting the initial data into the formula we get:
A= 103.2 J.
Power
Many machines and mechanisms perform the same work in different periods of time. To compare them, the concept of power is introduced.
Power is a quantity that shows the amount of work performed per unit of time.
Power is measured in Watts, after the Scottish engineer James Watt.
1 [Watt] = 1 [J/s].
For example, a large crane lifted a load weighing 10 tons to a height of 30 m in 1 minute. A small crane lifted 2 tons of bricks to the same height in 1 minute. Compare crane capacities.
Let's define the work performed by cranes. The load rises 30m, while overcoming the force of gravity, so the force expended on lifting the load will be equal to the force of interaction between the Earth and the load (F = m * g). And work is the product of forces by the distance traveled by the loads, that is, by the height.
For a large crane A1 = 10,000 kg * 30 m * 10 m/s2 = 3,000,000 J, and for a small crane A2 = 2,000 kg * 30 m * 10 m/s2 = 600,000 J.
Power can be calculated by dividing work by time. Both cranes lifted the load in 1 minute (60 seconds).
From here:
N1 = 3,000,000 J/60 s = 50,000 W = 50 kW.
N2 = 600,000 J/ 60 s = 10,000 W = 10 kW.
From the above data it is clearly seen that the first crane is 5 times more powerful than the second.