Podsumowanie wiadomości o magnetyzmie i elektromagnetyzmie

Before you start, prepare answers for the following topics.

1. What properties does a permanent magnetmagnetmagnet have?

2. Describe the shape of the magnetic fieldmagnetic fieldmagnetic field lines around the bar magnetbar magnetbar magnet.

3. Describe the Earth's magnetic field.

4. How do we divide the materials in terms of susceptibility to magnetization?

5. Describe the shape of the magnetic fieldmagnetic fieldmagnetic field lines around the conductorconductorconductor with the current.

6. Explain what the electromagnet is.

7. Explain what electrodynamic force is. Describe the principle of DC motor operation.

8. What is the phenomenon of electromagnetic induction?

9. Describe the operation of the transformer.

10. Characterize electromagnetic radiationelectromagnetic radiationelectromagnetic radiation.

1. What properties does a permanent magnetmagnetmagnet have?

A magnet is a body that attracts iron or attracts or repels other magnets.

Each magnet has two poles:

• north - marked with the symbol N,

• south - marked with S.

The magnet is a magnetic dipole. This means that dividing each magnet into two parts will create two magnets, each of which has two poles.

The magnet's like poles repel each other while unlike poles attract.

2. Describe the shape of the magnetic fieldmagnetic fieldmagnetic field lines around the bar magnetbar magnetbar magnet.

The space around the magnet, in which the magnetic force acts, is called the magnetic field. This field interacts at a distance with bodies containing iron, nickel or cobalt or with other magnets. The magnetic field is represented by field lines directly from the north pole to the south pole. The magnetic field is strongest near the poles.

3. Describe the Earth's magnetic field.

Earth creates a magnetic fieldmagnetic fieldmagnetic field around itself. The southern magnetic pole of the Earth lies near the geographic North Pole, and the north magnetic pole near the geographic South Pole. The magnetic poles of the Earth can be determined using a compass whose most important part is a small magnetic needle. It indicates the magnetic south pole or geographic North Pole. The magnetic field around the Earth is called the magnetosphere.

4. How do we divide the materials in terms of susceptibility to magnetization?

Due to the susceptibility to magnetization, we divide substances into:

• Ferromagnetic - strongly attracted by the magnetic field, also permanently magnetisable. These include iron, cobalt, nickel, neodymium and compounds and alloys of these metals. They are used, among others for the construction of permanent magnets, electromagnetelectromagnetelectromagnet cores, transformertransformertransformer cores, magnetic media, and holders.

• Paramagnetic - substances weakly attracted by the magnetic field. These include, for example: aluminium, sodium, and potassium, lithium.

• Diamagnetic - these substances are weakly repelled by the magnetic field. Copper and its alloys, graphite, bismuth, distilled water belong to this group.

5. Describe the shape of the magnetic fieldmagnetic fieldmagnetic field lines around the conductorconductorconductor with current.

If an electric current flows through a conductorconductorconductor, a magnetic fieldmagnetic fieldmagnetic field is created around this conductor. Its presence and direction can be determined with a magnetic needle or compass. Changing the direction of the current flow in the conductor causes a change in the direction of the magnetic field.

Magnetic field lines around the rectilinear conductor with current are in the shape of concentric circles. The direction of the magnetic field can be determined by the right hand rule.

6. Explain what the electromagnetelectromagnetelectromagnet is.

An electromagnetelectromagnetelectromagnet is a magnetmagnetmagnet created by the flow of electric current through a conductorconductorconductor. Most often, the electromagnet consists of a coil, through which current flows and a ferromagnetic core, which is designed to enlarge the magnetic field created by the current. Like magnets, electromagnets have two poles: north and south. The magnetic properties of the electromagnet disappear when we disconnect it from the voltage source. They are used for, among others lifting scrap, in locks and electromagnetic valves, accelerators, nuclear magnetic resonance devices.

7. Explain what electrodynamic force is. Describe the principle of DC motor operation.

If a conductor with electric current is placed in the magnetic fieldmagnetic fieldmagnetic field, the force, called the electrodynamic force, acts on it. The direction of the force is perpendicular to the direction of the current and perpendicular to the direction of the magnetic field.

This phenomenon is used in electric motors, in which electric energy is converted into mechanical energy. DC motor is built from a stator, or a system of magnets or electromagnets, and a rotor - a coil placed in a stator. The electrodynamic force created by the flowing current causes the rotation of the coil.

8. What is the phenomenon of electromagnetic induction?

If the conductorconductorconductor is placed in a variable magnetic fieldmagnetic fieldmagnetic field, then the electrical voltage is created. This phenomenon is called electromagnetic induction. A variable magnetic field can be created by the movement of a magnetmagnetmagnet or electromagnetelectromagnetelectromagnet. In the presence of a permanent magnetic field, the phenomenon of induction does not occur.

9. Describe the operation of the transformertransformertransformer.

A transformer is a device used to transfer the energy of an alternating current. With it, you can increase or decrease the electrical voltage of the induced current. It is built from the primary and secondary windings, which are placed on a common ferromagnetic core. The flow of alternating current in the primary winding induces current flow in the secondary winding. This is possible due to the phenomenon of electromagnetic induction.

10. Characterize electromagnetic radiationelectromagnetic radiationelectromagnetic radiation.

The electromagnetic wave is a disturbancedisturbancedisturbance of the electromagnetic field propagating in space. The properties of an electromagnetic wave depend on the wavelength. We distinguish radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X‑rays and gamma rays. Electromagnetic waves propagate in a vacuum at 300000 $\frac{km}{s}$.

The larger the wavelength, the lower its frequency, i.e. the wavelength and frequency are inversely proportional to each other.

Exercises

Exercise 2

Draw the magnetic field lines.

a) Around a bar magnet,

b) Between two bar magnets, with the north and south poles facing each other, and a gap between them.

c) Between two bar magnets, with the north poles facing each other, and a gap between them.

Show solution

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Na rysunku w punkcie a pokazane jest pole magnetyczne wokół magnesu sztabkowego ułożonego poziomo, kierunek pola zaznaczony jest strzałkami skierowanymi od N do S. W punkcie b opisanym unlike pole attraction zaznaczony jest przebieg pola magnetycznego między dwoma magnesami zwróconymi ku sobie przeciwnymi biegunami, kierunek pola zaznaczony jest strzałkami skierowanymi od N magnesu po lewej do S magnesu po prawej. W punkcie c pokazane są dwa magnesy zwrócone do siebie tymi samymi biegunami N i linie sił pola tych magnesów, kierunek pola zaznaczony jest strzałkami skierowanymi od N każdego z magnesów na zewnątrz.

Glossary

Keywords

bar magnetbar magnetbar magnet

electrodynamic inductionelectrodynamic inductionelectrodynamic induction

electromagnetelectromagnetelectromagnet

magnetmagnetmagnet

magnetic fieldmagnetic fieldmagnetic field