Topic: Light and sound

Supplementary material for use in lessons in the group of natural sciences (nature, biology, chemistry, geography, physics), additional classes, science clubs. It can serve as a resource for expanding knowledge, preparing students for science competitions.

Target group
Students of elementary school – physics

Core curriculum

General aim of education

Students compare the speed of sound and light propagation.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• explain the speed of sound in the air;

• explain that nothing can move faster than light.

Methods/techniques

• expository

  • talk.

• activating

  • discussion.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Before classes

• Students get acquainted with the content of the abstract. They prepare to work on the lesson in such a way to be able to summarize the material read in their own words and solve the tasks themselves.

Introduction

• The teacher explains the aim of the lesson and together with students determines the success criteria to be achieved.

• The lecturer, referring to the previous classes, formulates questions to which the students or volunteers indicated by him respond: How does the sound arise? What is a sound wave?.

• The teacher asks pupils to recall the rules of behavior during the storm and explain how to know that a storm is approaching.

Realization

• Students read the fragment „Speed of sound” and then independently perform interactive exercise No. 1.

• The teacher presents the following problem for students to consider: The distance from Earth to the Sun is 150,000,000 km. Flying at the maximum speed that is allowed on Polish highways (ie 140km / h), we would reach the Sun in about 115 years. Meanwhile, the light from the Sun reaches the Earth in about 8.5 minutes. What should I do to make the flight on the Sun shorter? Students present their ideas, the teacher writes them on the board.

• Students read the fragment „Faster or slower than the light?” and re‑analyze the suggestions on the board. Together, they formulate conclusions.

• The teacher asks pupils to show examples of simultaneous use of sound and light. Displays interactive illustration („Lighthouse”) and asks students to explain why emergency vehicles use both light and sound signals.

• The instructor recommends the pupils to read the fragment „How far away is the storm?” And then they wrote „Task 1”.

Summary

• Students independently perform interactive exercise No. 2.

Homework

• Develop a lap book containing issues learned during the lesson and bring your work to the next class.

• Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Light and sound

We already know that the sound is a wave that can travel only through a medium comprised of particles. The speed of sound travel depends on the density of these particles. In air, just above the ground, sound travels with the speed of 340 m/s (1224 km/h). Therefore, it needs approximately 3 seconds to travel a kilometre. As the altitude increases, air becomes increasingly thinner and the speed of sound decreases – for instance, at the altitude of 10 km it travels with the speed of only 1080 km/h. In water, on the other hand, sound travels at the speed of approximately half a kilometre per second!
What happens when there is no medium? In such case we are dealing with a place exposed to vacuum. There are no particles that could transfer vibrations between one another and carry the sound wave. Sound cannot travel in these conditions. This occurs in space – you cannot hear any sound in space.

Why is it that during a storm we first see a flash and only later hear thunder? Light in a vacuum travels with the astounding speed of 300,000 km/s! Moreover, this is the greatest speed in nature and no body is able to achieve it. When light enters the atmosphere or another medium, it slightly slows down as in contrast to sound it travels at its fastest speed in vacuum. In air, light travels slightly slower – with the speed of 291 thous. km/s. Nevertheless, its speed still remains many times greater than the speed of sound.

During a lightning strike, the air gets very hot. For this reason, it becomes a source of light as well as sound. The difference between the speed of sound and light means that we first see the lightning flash and only then hear the thunder that accompanies a discharge.
By using the difference in the speed with which sound and light travel, we are able to approximate the distance between our location and the storm. When you see a lightning flash, start counting the seconds until you hear the sound of thunder. Keeping in mind that sound needs approximately 3 seconds to travel a kilometre, we’re able to approximate how far away is the storm. For instance, if the thunder reaches 12 seconds after the flash, the storm is raging 4 km away (12:3=4).

• The speed of the sound depends on the medium through which it travels.

• The speed of the sound in air at sea level is 340 m/s

• Sound doesn’t travel through vacuum.

• Light travels faster than any body in the world.