2. Light has characteristics of both
a particle and a wave
• Light has properties of both particles and waves.
• A wave characterized by a wavelength, denoted by the Greek letter lambda, which is
the distance between successive wave crests.
• The frequency, represented by the Greek letter nu (v), is the number of wave crests that
pass an observer in a given time.
• A simple equation relates the wavelength, the frequency, and the speed of any wave:
•
3. • Where c is the speed of the wave—in the present case, the speed of light (3.0✖️ 108 m
s–1).
• The light wave is a transverse (side-to-side) electromagnetic wave, in which both
electric and magnetic fields oscillate perpendicularly to the direction of propagation
of the wave and at 90° with respect to each other.
4. In physics, the term light refers to electromagnetic radiation of any wavelength, whether
visible or not. in this sense, gamma rays, x-rays, microwaves and radio waves are also
light. Like all types of light, visible light is emitted and absorbed in tiny "packets" called
photons and exhibits properties of both waves and particles. This property is referred to
as the wave–particle duality. The study of light, known as optics.
5. • Light is also a particle, which we call a photon. each photon contains an amount of energy that is called a
quantum (plural quanta).
• The energy content of light is not continuous, but rather is delivered in these discrete packets, the
quanta. the energy (e) of a photon depends on the frequency of the light according to a relation known as
planck’s law:
E = hv
• Where h is planck’s constant (6.626 ✖️ 10–34 J S).
• Sunlight is like a rain of photons of different frequencies. our eyes are sensitive to only a small range of
frequencies, the visible-light region of the electromagnetic spectrum.
• Light of slightly higher frequencies (or shorter wavelengths) is in the ultraviolet region of the spectrum,
and light of slightly lower frequencies (or longer wavelengths) is in the infrared region.
6.
7. • The output of the sun is shown in Figure 7.3, along with the energy density
that strikes the surface of Earth.
• The absorption spectrum of chlorophyll a (curve C in Figure 7.3) indicates
approximately the portion of the solar output that is utilized by plants.
• An absorption spectrum (plural spectra) displays the amount of light energy
taken up or absorbed by a molecule or substance as a function of the
wavelength of the light.
