PS.7 The student will investigate and understand the characteristics of transverse waves. Key concepts include
1. characteristics of electromagnetic radiation, including visible light
2. regions of the electromagnetic spectrum have specific characteristics and uses

Electromagnetic radiation, including visible light

Radiant energy travels through space in transverse waves of varying lengths and frequencies.

• The different wavelengths and frequencies of radiant energy are referred to as electromagnetic radiation.
  
  • Electromagnetic radiation consists of changing electric and magnetic fields.
  • All types of electromagnetic radiation travel at the speed of light but differ in frequency.
• The sun gives off radiant energy of all frequencies in the electromagnetic spectrum.

• The energy transmitted by various wavelengths of radiant energy (electromagnetic radiation) may be converted to other forms of energy only after it is absorbed by matter.
• Scientists have divided the wavelengths of electromagnetic radiation (radiant energy) into a spectrum.
  • Electromagnetic waves are arranged on the electromagnetic spectrum according to wavelength and frequency.

Electromagnetic Spectrum

• The electromagnetic spectrum includes
  • gamma rays
  • X-rays
  • ultraviolet
  • visible light
  • infrared
  • microwaves
  • radio waves
• Radio waves are the lowest-energy waves and have the longest wavelength and the lowest frequency.
• Gamma rays are the highest energy waves and have the shortest wavelength and the highest frequency.
• Visible light lies in between and makes up only a small portion of the electromagnetic spectrum.

Materials Reflect, Absorb, or Transmit Radiant energy

• Radiant energy travels in straight lines until it strikes an object where it can be reflected, absorbed, or transmitted.
• When a wave encounters a new material, the new material may absorb the energy of the wave by transforming it to another form of energy, usually thermal energy.
  • The material may reflect the wave or the material may transmit the wave, allowing it to pass through .
• When visible light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object's material and the frequency (color) of the light.
• The color of an object is due to the wavelengths of reflected visible light coming from the object to the viewer's eye.
  • For example, when a ball looks blue, it is because it reflects blue light wavelengths; other wavelengths of visible light are absorbed by the ball.
  • A black object absorbs all wavelengths of visible light .

Mirrors & Reflection

• Mirrors reflect light.
• The direction of the reflected light rays is predicted by the law of reflection.
• The law of reflection states that the incident light ray, the reflected light ray, and the normal surface of the mirror all lie on the same plane.
• Furthermore, the angle of reflection is equal to the angle of incidence .


• A concave mirror focuses light rays to a point and produces an upright, magnified image if the mirror is close to the object (e.g., make-up mirrors).
• If the concave mirror is far from the object, the image is inverted and smaller than the object.
• A convex mirror spreads light rays and produces only upright, smaller images.



Lenses & Refraction

• The path that light travels can be traced as straight lines, except at surfaces between different transparent materials (e.g., air and water, air and glass) where the light path bends.

• As visible light travels through different media, it undergoes a change in speed that may result in refraction.
• Lenses refract visible light rays.
• When visible light enters a lens, it bends toward the thickest part of the lens .


• Optical instruments such as cameras, telescopes, binoculars, and microscopes use lenses and combinations of lenses to change the path of light rays and produce a specific type of image.

• A concave lens spreads light rays, forming a smaller, upright image.
• A convex lens focuses light rays to a point.
• When the object is far from the lens, the image formed is smaller and inverted.
• When the object is close to the convex lens, the image is larger than the object and is upright .

Uses of Electromagnetic Radiation

• Electromagnetic radiation has many practical uses in everyday life, such as in medicine, security, and telecommunications.
• Electromagnetic radiation is used for communications and transmission of information.
• The waves that are used in this way are radio waves, microwaves, infrared radiation, and visible light.
• Digitized signals encode and transmit information more reliably than analog signals.

You should understand
• the types of electromagnetic waves, including visible light in terms of wavelength, frequency, and energy
• how waves are reflected, absorbed, or transmitted through various materials
• why objects appear as specific colors
• characteristics of images formed by concave, convex, and plane mirrors  and by concave and convex lenses
• uses of mirrors and lenses in everyday life
• describe an everyday application of each of the major forms of electromagnetic energy.