Waves Objectives State the law of reflection Compare

Waves

Objectives • State the law of reflection. • Compare and contrast refraction and diffraction. • Identify wave interference. • CLE 3202. 2. 1 Investigate the properties and behaviors of mechanical and electromagnetic waves.

The Behavior of Waves • Reflection occurs when a wave strikes an object and bounces off of it

Reflection - the bouncing back of a wave. 1) Sound echoes 2) Light images in mirrors 3) Law of reflection i = r

• All types of waves can be reflected • The angle of incidence of a wave is always equal to the angle of reflection

The Behavior of Waves • Normal – an imaginary line perpendicular to a reflective surface • Angle of incidence – the angle formed by the wave striking the surface and the normal

• Angle of reflection – the angle formed by the reflected wave and the normal

A. Reflection Normal • Reflection – when a wave strikes an object and bounces off incident beam reflected beam

Incidence – Reflection w/Normal

The Behavior of Waves • Refraction – the bending of a wave caused by a change in its speed as it moves from one medium to another

The Behavior of Waves • The greater the change in speed is, the more the wave bends • When a wave passes into a material that slows it down, the wave is bent toward the normal • When a wave passes into a material that speeds it up, the wave is bent away from the normal

Refraction of Light in Water • Light waves travel slower in water than in air. This causes light waves to change direction when they move from water to air or air to water. • When light waves travel from air to water, they slow down and bend toward the normal.

• Prism refracts the light twice once when it enters the prism and again when it leaves the prism.

B. Refraction • Example: View explanation.

Diffraction • Diffraction - the bending of a wave around the edge of an object.

1) Water waves bending around islands 2) Water waves passing through a slit and spreading out

3. Diffraction depends on the size of the obstacle or opening compared to the wavelength of the wave. Less occurs if wavelength is smaller than the object. More occurs if wavelength is larger than the object.

4) AM radio waves are longer and can diffract around large buildings and mountains; FM can’t.

Wave Interference • Interference – the ability of two or more waves to combine and form a new wave

The Behavior of Waves • Waves pass right through each other and continue in their original direction • New wave exists only while the two original waves continue to overlap

The Behavior of Waves • Constructive interference – waves add together

The Behavior of Waves • Destructive interference – waves subtract from each other

D. Interference • Interference – constructive brighter light – destructive dimmer light

The Behavior of Waves • Standing waves – a wave pattern that stays in one place • Form when waves of equal wavelength and amplitude that are traveling in opposite directions continuously interfere with each other

Standing wave Nodes – the places where two waves always cancel each other node antinode

Nodes

• Resonance – the ability of an object to vibrate by absorbing energy at its natural frequency

How do you think wave behaviors apply to music? Constructive interference causes sound waves to become louder; destructive interference causes sound waves to become more quiet. Standing waves create rich, even, constant tones in music.

Section Check 2 Question 2 What is the difference between refraction and reflection? Answer Refraction occurs if a light wave changes speed in moving from one material to another. Reflection occurs when light waves are returned or thrown back from a surface.

Sonic Boom vs Boom Cone