Topicme79c203f58ff1bee_1528449000663_0Topic

Ranges of electromagnetic wavelengthwavelengthwavelength and their application

Levelme79c203f58ff1bee_1528449084556_0Level

Third

Core curriculumme79c203f58ff1bee_1528449076687_0Core curriculum

IX. Waves and optics. The student:

6) distinguishes transverse and longitudinal waves; describes light as an electromagnetic waveelectromagnetic waveelectromagnetic wave; describes the polarization of light resulting from the transverse nature of the wave;

7) describes the spectrumspectrumspectrum of white light as a mixture of waves at different frequencies.

Timingme79c203f58ff1bee_1528449068082_0Timing

45 minutes

General learning objectivesme79c203f58ff1bee_1528449523725_0General learning objectives

Explains what electromagnetic waves are.

Key competencesme79c203f58ff1bee_1528449552113_0Key competences

1. Calculates frequencies and wavelengths of light.

2. Describes different types of electromagnetic waves.

Operational (detailed) goalsme79c203f58ff1bee_1528450430307_0Operational (detailed) goals

The student:

- explains what electromagnetic waves are,

- describes different types of electromagnetic waves.

Methodsme79c203f58ff1bee_1528449534267_0Methods

1. Discussion.

2. Text analysis.

Forms of workme79c203f58ff1bee_1528449514617_0Forms of work

1. Individual work.

2. Group work.

Lesson stages

Introductionme79c203f58ff1bee_1528450127855_0Introduction

Remind what the spectrumspectrumspectrum of electromagnetic radiation looks like.

Procedureme79c203f58ff1bee_1528446435040_0Procedure

The properties of electromagnetic radiation, or electromagnetic waves, are described by several parameters. These include wave frequencyfrequencyfrequency, wavelengthwavelengthwavelength, periodperiodperiod and amplitudeamplitudeamplitude. In the graphic description of the wave, the following concepts are also helpful: the peak, the troughtroughtrough, the rest position.

[Interactive graphics]

Definitions:

WavelengthwavelengthWavelength (symbol: $\lambda$, unit: m) is the distance between two points of maximum displacement of a wave, i.e. between successive peaks (or troughs). The longer the wave, the smaller its energy.

Amplitude (symbol: A, unit: m) is the maximum displacement of a given wave point from the rest position. The higher the amplitudeamplitudeamplitude, the higher the wave intensity.

FrequencyfrequencyFrequency (symbol: f, unit: Hz) is the number of full displacements of a given wave point from the rest position made within 1 second.

PeriodperiodPeriod (symbol: T, unit: s) is the time required for the given wave point to cover the distance equal to the wavelength:

Wave speedwave speedWave speed (symbol: c - in a vacuum, v - in any medium, unit: $\frac{m}{s}$) - the speed with which a given wave point propagates in space. Electromagnetic waves in a vacuum move at the speed of light:

[Illustration 1]

Task 1

The figure shows two electromagnetic waves:

1. Which wave has the greater intensity?
2. Which wave corresponds to higher‑energy radiation?
3. Which wave represents green light and which represents infrared radiation?

[Illustration 2]

Answer:

1) a,
2) b,
3) b - green light, a - infrared radiation.

Task 2

Compare the results of X‑ray measurements with radio waves:

1. Which one is moving at a higher speed?
2. Which one has a longer wavelengthwavelengthwavelength?
3. Which of them has a higher frequency?

Answer:

1. Both types of radiation belong to electromagnetic waves, so they move at the same speed.
2. Radio waves are longer than X‑ray waves.
3. X‑rays have a higher frequencyfrequencyfrequency.

Task 3

The global positioning system (GPS) that we use in mobile phones or navigation devices, e.g. in cars, requires very accurate timing and reading of the position of the satellites on the orbits. Each of the satellites uses an atomic clock that sends signals using two frequencies of 1575,42 MHz and 1227,6 MHz. Calculate the wavelengths that these frequencies correspond to. Specify what kind of waves they belong to.me79c203f58ff1bee_1527752256679_0The global positioning system (GPS) that we use in mobile phones or navigation devices, e.g. in cars, requires very accurate timing and reading of the position of the satellites on the orbits. Each of the satellites uses an atomic clock that sends signals using two frequencies of 1575,42 MHz and 1227,6 MHz. Calculate the wavelengths that these frequencies correspond to. Specify what kind of waves they belong to.

Answer:

19,029 cm and 24,421 cm, these are microwaves.

Task 4

Popular laser pointers usually emit green, red and blue light. Search on the Internet for the wavelengths corresponding to the colour of light emitted by these pointers. Then calculate what frequencies they correspond to. Are pointers also available with different colours?

Compare how far the light beam of these pointers can reach.

What should you pay attention to when using them?

[Illustration 3]

Lesson summaryme79c203f58ff1bee_1528450119332_0Lesson summary

Electromagnetic waves are widely used in technology and medicine. We use them in everyday life using, for example, mobile phones, using satellite navigation, microwave ovens, doing examinations recommended by a doctor.me79c203f58ff1bee_1527752263647_0Electromagnetic waves are widely used in technology and medicine. We use them in everyday life using, for example, mobile phones, using satellite navigation, microwave ovens, doing examinations recommended by a doctor.

Selected words and expressions used in the lesson plan

amplitudeamplitudeamplitude

peakpeakpeak

electromagnetic waveelectromagnetic waveelectromagnetic wave

frequencyfrequencyfrequency

periodperiodperiod

spectrumspectrumspectrum

troughtroughtrough

wave speedwave speedwave speed

wavelengthwavelengthwavelength