Laboratory work in physics for 8th grade: “Measurement of power and work of current in an electric lamp”

How to choose the right lighting for a room?

I could compare the power of LED lamps and incandescent lamps right now, you would see what you need and that’s it. But I want you to not just choose a lamp, but to understand how it works. Knowing the lighting standards and the area of ​​the room, we can choose exactly the LED lamp we need.

First, let's look at the illumination standards in lux per square meter:

Based on what you already know, calculating the necessary lighting will not be difficult for you. Let's say we have a room 5 by 6 meters, we are going to relax in it, so let's take the illumination to 54. The area of ​​the room will be 5 x 6 = 30 meters. We multiply the illumination by the area and get the number of Lumens. 54 times 30 is 1620 lumens or lm. All that remains is to find such an LED lamp or buy two of 800 lumens.

LED lightening

This was the most accurate and correct way to select the power of an LED lamp. But we can still focus on the power consumption of incandescent lamps or even LED lamps.

Principle of operation

The source works by emitting wave radiation due to electronic molecular excitation and atoms, as well as due to thermal vibration of the filament molecular nucleus. As the temperature of the filament increases, the translational, vibrational and rotational energy of charged particles increases. As a result, the flux of radiation with average photon energy increases. The radiative wavelength moves into the short-wave infrared and long-wave visible regions. In the future, the body temperature will increase, providing energy that is sufficient to excite molecules and atoms and produce short-wave visible radiation. Therefore, the main factor that determines density with radiation wavelength is temperature.

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Operating principle of incandescent lamps

Electric circuits and their varieties

An electrical circuit is a complex of devices and individual objects that are connected in a given way. They provide a path for electrical current to pass. To characterize the ratio of the charge flowing within each individual conductor over a period of time to the duration of this time, a certain physical quantity is used. And this is the current strength in an electrical circuit.

Such a circuit includes an energy source, energy consumers, i.e. load and wires. They are divided into two types:

• Unbranched - the current moving from the generator to the energy consumer does not change in value. For example, this is lighting that includes only one light bulb.
• Branched - chains that have some branches. The current, moving from the source, is divided and goes to the load along several branches. At the same time, its meaning changes.

An example would be lighting that includes a multi-arm chandelier.

A branch is one or more components connected in series. The current flows from the node with high voltage to the node with its minimum value. In this case, the incoming current at the node coincides with the outgoing one.

Circuits can be nonlinear and linear. If in the former there are one or more elements where there is a dependence of the values ​​on current and voltage, then in the latter the characteristics of the elements do not have such a dependence. In addition, in circuits characterized by direct current, its direction does not change, but under the condition of alternating current, it changes taking into account the time parameter.

Interesting info on the topic

A three-phase power supply circuit is used in production. The total voltage of such a network is 380 V. Also, such wiring is installed in multi-story buildings, and then distributed to apartments. But there is one nuance that affects the final voltage in the network - connecting the voltage core results in 220 V. Three-phase, unlike single-phase, does not cause distortions when connecting power equipment, since the load is distributed in the panel. But to connect a three-phase network to a private house, special permission is required, so a scheme with two cores, one of which is zero, is widespread.

Current calculation for a single-phase network

Current is measured in amperes. To calculate power and voltage, the formula is I = P/U, in which P is the power or total electrical load measured in watts. This parameter must be entered in the technical data sheet of the device. U – represents the voltage of the calculated network, measured in volts.

The relationship between current and voltage is clearly visible in the table:

Thus, the relationship between power and current makes it possible to perform preliminary calculations of loads in a single-phase network. The calculation table will help you select the required wire cross-section, depending on the parameters.

Resistance change:

In the following diagram you can see the difference in resistance between the systems shown on the right and left side of the figure. The resistance to water pressure in the tap is counteracted by the valve; depending on the degree of opening of the valve, the resistance changes.

Resistance in a conductor is depicted as a narrowing of the conductor; the narrower the conductor, the more it opposes the passage of current.

You may notice that on the right and left sides of the diagram the voltage and water pressure are the same.

You need to pay attention to the most important fact. Depending on the resistance, the current increases and decreases

Depending on the resistance, the current increases and decreases.

On the left, with the valve fully open, we see the largest flow of water. And at the lowest resistance, we see the largest flow of electrons (Amperage) in the conductor.

On the right, the valve is closed much more and the flow of water has also become much greater.

The tension of the conductor also decreased by half, which means the resistance to the flow of current doubled. As we can see, due to the high resistance, half as many electrons flow through the conductor.

For reference

Please note that the constriction of the conductor shown in the diagram is used only as an example of resistance to current flow. In real conditions, the narrowing of the conductor does not greatly affect the flow of current

Semiconductors and dielectrics can provide significantly greater resistance.

The tapering conductor in the diagram is shown only as an example, to understand the essence of the process taking place. The formula of Ohm’s law is the relationship between resistance and current

I = E/R As you can see from the formula, the current is inversely proportional to the resistance of the circuit.

More resistance = Less current

* provided that the voltage is constant.

How is the luminous flux of an LED lamp measured?

LED bulbs

As I already said, the luminous flux of an LED lamp or any other light source can be measured in Lumens. On lamp packaging, Lumens are abbreviated as Lm or Lm. Before moving on to the calculations, it is important to understand what Lumen is. Let's imagine that our light bulb is a bag of sand from which sand is constantly pouring out; imagine that one lumen is one grain of sand. The number of lumens for our bag bulb will mean how many grains of sand will fall on one square meter of surface, for example, 900 lumens will mean that 900 grains of sand will fall on one square meter.

But we don’t have ordinary sand, but light, and it is scattered evenly over the entire surface, so if the luminous flux of a lamp is 900 lumens, and the area of ​​the room is 3 square meters, then 300 lumens will fall per square meter.

And here we come to another very important parameter - the illumination of the room. Lumens characterize only the luminous flux of the lamp; if we continue our analogy, then the amount of sand that can spill out of the bag. But there is another parameter - this is the illumination of the room and it is measured in lux. Lux shows how many lumens will fall per square meter in a certain room. Designated Lk or Lx. If we said that our light source emits 900 Lumens, and the area is three square meters, then the illumination of our room will be 300 lux. For those who really love the formula 1 lux = 1 lumen / 1 square meter.

Got it? Now let's move on to the question of how to find out the lighting power of LED lamps.

Characteristics

Alternating current flows through a circuit and changes its direction with magnitude. Creates a magnetic field. Therefore, it is often called periodic sinusoidal alternating electric current. According to the law of a curved line, its value changes after a specific period of time. That's why it's called sinusoidal. Has its own parameters. The important ones are to indicate the period with frequency, amplitude and instantaneous value.

A period is the time during which the electric current changes, and then it repeats again. Frequency is the period per second. Measured in hertz, kilohertz and millihertz.

Amplitude is the maximum current value with voltage and flow efficiency over a full period. Instantaneous value is an alternating current or voltage that occurs during a specific time.

AC Characteristics

Kinds

Today there are a large number of different lamps, which are divided according to the shape and coating of the bulb, purpose and filler. It can be spherical, cylindrical, tubular and spherical; transparent, mirror and matte. There are also light sources for general, local and quartz-halogen purposes. In addition, there are vacuum, argon, xenon, krypton and halogen models.

Transparent ones are common options. Such elements are considered the cheapest and most effective; they have an uneven light flow. Mirror models are the most effective in terms of lighting, since the coating generates directional light flow. Matte ones are able to create soft and diffuse lighting for favorable working and leisure conditions. Products with local lighting operate at twelve volts, which is necessary to create safe working conditions.

Note! Such lamps are needed to illuminate inspection holes during the installation of electrical garage wiring.

Incandescent lamp types table

General purpose lamps

General-purpose sources are the most common light sources that are used to illuminate an apartment or factory on a network with an alternating current of 220 volts and a frequency of up to 50 hertz. There are vacuum, argon and krypton. The same group is neodymium and krypton. Essentially these are ordinary lighting lamps. It is worth pointing out that at the time of manufacturing neodymium sources, neodymium oxide is used, which absorbs the light spectrum. This improves the light quality.

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Widespread use of general purpose luminaires

Spotlight lamps

Spotlight sources are installed on ship, railway, theater and other searchlights. They differ in that they have an increased light output and can be supplemented with reflectors to improve the concentration of the light beam.

Spotlights as one of the types

Mirror lamps

Mirror light sources are distinguished by the fact that they have the usual bulb shape and a special internal coating of the bulb part. This helps to collect all the light flow, which is directed in the right direction. They are used in industry, videography, farming and bathroom ceiling lighting.

Halogen lamps

Halogen lamps are powered by an inert gas, to which bromine and iodine are added to protect the filament and increase operating life. Such light sources are small in size for use as a filler of expensive inert gas. They are distinguished by their brightness, natural color rendering, good service life and significant luminous efficiency, having smaller dimensions.

Note! The only negative is the sensitivity and significant changes in mains voltage.

Halogen lamps as one of the types