Praca prądu elektrycznego

Prepare answers to the following introductory questions for the lesson.

1. What is electric currentelectric currentelectric current?

2. What is the current intensity?

3. What is voltagevoltagevoltage?

4. Introduce Ohm's law.

5. What determines the resistance of a conductorconductorconductor?

The definition of voltage as a formula:

From the above formula it is easy to determine the work done by electric forces:

Usually, in practice, we rarely know what charge has flown through a given electricity receiver. However, in a fairly simple way we can measure the current flowing through it.

Using the definition of electric currentelectric currentelectric current:

we can directly determine the charge that has flown through the electricity receiver:

After inserting this to the formula for work, we will get the final formula:

where:
W - work done by electric forceselectric forceselectric forces,
U - voltagevoltagevoltage at the ends of the electricity receiver,
I - the intensity of current flowing through the electricity receiver,
t - duration of the current flowcurrent flowcurrent flow.

What are the effects of the current flow?

Thermal

Example:

Electrons in a heating element of iron collide constantly with atoms, stimulating them to vibrate. Increased vibration of atoms is equivalent to increased temperature of the heating element of iron.

Mechanical

Example:

The current flowing in the engine forces the interaction between the magnets inside the engine and the moving parts of the engine, causing them to rotate.

Light

Example:

Electrons, colliding with the atoms of the filament of the light bulb, heat it up and stimulate to glow.

Magnetic

Example:

The electric currentelectric currentelectric current flowing in the winding of the electromagnet creates a magnetic field in the iron core.

Chemical

Example:

The current flowcurrent flowcurrent flow through the aqueous sulfuric acid solution causes the disintegration of water molecules and the production of hydrogen and oxygen.

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Pokaz slajdów – skutki przepływu prądu. Instrukcja obsługi z poziomu klawiatury: 1. Uruchomienie aplikacji - ENTER, 2. Na każdym ze slajdów czytany jest automatycznie tekst alternatywny po polsku, 3. Przy pierwszym uruchomieniu na pierwszym slajdzie, czytanie tekstu po angielsku - TAB, 4. Przejście między slajdami: do następnego slajdu - TAB, do poprzedniego slajdu - TAB + SHIFT, 5. Przejście do czytania napisu po angielsku - strzałka w górę + strzałka w dół (czyta tekst po angielsku widoczny na slajdzie).

Pokaz slajdów – skutki przepływu prądu. Instrukcja obsługi z poziomu klawiatury: 1. Uruchomienie aplikacji - ENTER, 2. Na każdym ze slajdów czytany jest automatycznie tekst alternatywny po polsku, 3. Przy pierwszym uruchomieniu na pierwszym slajdzie, czytanie tekstu po angielsku - TAB, 4. Przejście między slajdami: do następnego slajdu - TAB, do poprzedniego slajdu - TAB + SHIFT, 5. Przejście do czytania napisu po angielsku - strzałka w górę + strzałka w dół (czyta tekst po angielsku widoczny na slajdzie).

Zasób interaktywny dostępny pod adresem https://zpe.gov.pl/a/D1A6B3CGu

The basic formula describing the work of electric currentelectric currentelectric current (DC current):

sometimes is not very easy to use. But we can modify the above formula a bit depending on our needs. We must make use of Ohm's law.

1. We substitute the expression for voltagevoltagevoltage $U=IR$ derived from Ohm's law. We then get:

2. We substitute the expression for current $I=\frac{U}{R}$ derived from Ohm's law. We then get:

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Zdjęcie prezentuje nowy licznik energii elektrycznej przygotowany do zainstalowania w mieszkaniu.

If we look closely at the above figure, we will discover the symbol [kWh]. This is called kilowatt‑hour. It is a unit of work done by electric current.

Whether we want it or not, we always pay for the work done, because we use large amounts of energy in domestic electrical installations, it is easier to express the energy consumed in [kWh].

Summary

• The work of electric currentelectric currentelectric current is calculated from the formulas: $W=UIt$ or $W=I^{2}Rt$ or $W=\frac{U^{2}t}{R}$.

• The unit of electricity is Joule [J] but more often kilowatt‑hours [kWh] are used.

• One kilowatt‑hour is equal to electricity consumed within 1 hour by a 1 kW receiver. It is equal to 3,6 megajoules: 1 kWh = 3,6 MJ.

Exercises

Glossary

Keywords

current flowcurrent flowcurrent flow

electric currentelectric currentelectric current

voltagevoltagevoltage