Podsumowanie wiadomości o elektryczności

Prepare the answers to the repetition questions from the electric currentelectric currentelectric current.

1. What is electric current?

2. What is the intensity of electric current?

3. What is the unit of electric current?

4. What is the name of the device used to measure the intensity of electric current?

5. Present Kirchhoff's law.

6. What determines the intensity of the electric current flowing through the conductor?

7. What is Ohm's law about?

8. What is the electrical resistance?

9. What is the unit of electrical resistance?

10. Is the resistance of the conductor dependent on the temperature?

11. What determines the resistance of the conductor?

12. List two basic ways to connect electric receivers.

13. Characterize the series connection of electric receivers.

14. Characterize the parallel connection of electric receivers.

15. What is the work of electric current?

16. How can you determine the work of electric current?

17. How can you determine the power of electric current?

18. What is the nominal power?

19. What is the voltage?

20. What is the voltage unit and what device is used to measure the voltage?

1. What is electric current?

Electric current is an orderly movement of electric charges.

2. What is the intensity of electric current?

The intensity of electric current is the ratio of the charge flowing through the cross‑section of the conductor to the flow time.

3. What is the unit of electric current?

The unit of electric currentelectric currentelectric current is 1 A (ampere).

4. What is the name of the device used to measure the intensity of electric current?

The ammeter is used to measure the intensity of electric current.

5. Present Kirchhoff's law.

In circuits with electric currentelectric currentelectric current we often have branches. It follows from the principle of charge conservation that the sum of currents flowing into the node (junction) is equal to the sum of currents flowing out of that node. This law is called the 1st Kirchhoff’s law.

6. What determines the intensity of the electric current flowing through the conductor?

The intensity of the electric current flowing through the conductor depends on the voltage between its ends. The dependence I(U) is called the current‑voltage characteristic.

7. What is Ohm's law about?

Ohm's law for a circuit section says that the current is directly proportional to the applied voltage.

8. What is the electrical resistance?

The voltage to current ratio, constant for a given section of the circuit, is called electrical resistanceresistanceresistance.

9. What is the unit of electrical resistance?

The unit of electrical resistanceresistanceresistance is 1 Ω (ohm).

10. Is the resistance of the conductor dependent on the temperature?

The resistance of the conductor is constant, if its temperature does not change. As the temperature increases, the resistanceresistanceresistance of the metallic conductor increases.

11. What determines the resistance of the conductor?

The electrical resistance of the conductor is directly proportional to its length and inversely proportional to the cross‑section.

The factor ρ is called the correct resistivity and is characterized by the type of material.

12. List two basic ways to connect electric receivers.

Electric receivers can be connected in series or in parallel.

13. Characterize the series connection of electric receivers.

The same current flows through all electric receivers connected in series. The voltage between the ends of the entire circuit is equal to the sum of voltages on individual receivers. The equivalent resistance of electric receivers connected in series is equal to the sum of individual resistances.

14. Characterize the parallel connection of electric receivers.

The same voltage is between the ends of all electric receivers connected in parallel. The current in the circuit is the sum of the currents flowing through individual receivers. The inverse of the equivalent resistanceresistanceresistance of the electric receivers connected in parallel is the sum of the inverse of the individual resistances.

15. What is the work of electric current?

Electric currentelectric currentElectric current are the charges flowing under the influence of Coulomb forces. These forces work in the conductor to move these charges. We call it the work of electric current or electric energy supplied to the conductor from the source.

16. How can you determine the work of electric current?

We can express the work of electric current in three ways:

We express the work in joules, but we can also express it in kilowatt‑hours: 1 kWh = 3600000 J.

17. How can you determine the power of electric currentpower of electric currentpower of electric current?

The power of a device that draws electric current can also be calculated using three formulas:

18. What is the nominal power?

On the electric energy receivers, the nominal power is often marked, i.e. the power that is dissipated on the receiver when it operates in the conditions described in the instructions. If the receiver is connected to another voltage, the power will be different.

19. What is the voltage?

The current in the external circuit flows from „+” to „-”, in other words in the direction of the electric forces, but inside the source the charges have to move from „-” to „+”. The cell must therefore be capable of performing work in order to move the charges from a point with lower potential to a point of higher potential. The ratio of this work to the transferred charge is called the cell voltage:

To allow the flow of current in the conductor we must maintain the potential difference at its ends. Voltage sources can be, for example, cells, batteries, accumulators.

20. What is the voltage unit and what device is used to measure the voltage?

The voltage unit is 1 V (volt). The voltage is measured with a voltmeter.

Summary

We dedicated this section to electricity. We described this phenomenon exactly, we defined the current intensity and its unit - ampere. We paid attention to the fact that the condition of an electric current in the electric circuit is to connect the load to the voltage source and to close the electrical circuit. We formulated Ohm's law and defined the concept of electrical resistanceresistanceresistance. We showed how to build simple electrical circuits, and how to draw and interpret their diagrams. You already know how to use a universal meter that can act as an ammeter or voltmeter. We have brought the concept of electric energy, i.e. the work of electric current, and its power. You can calculate these quantities in SI units, as well as those outside of this system, but commonly used in Poland.

Exercises

Glossary

Keywords

electric currentelectric currentelectric current

Ohm’s lawOhm’s lawOhm’s law

resistanceresistanceresistance