OPTICS from 1 mm to around 30 cm.

Microwave radiation is commonly referred to as

microwaves. They fall between infrared radiation and radio waves in the
Optics is a branch of physics that deals with the determination of electromagnetic spectrum. A few of the properties of microwaves are as
behavior and the properties of light, along with its interactions with the matter follows:
and also with the instruments which are used to detect it.  Metal surfaces reflect microwaves. Microwaves with a certain
Optics, in a simple manner, is used to describe the behavior of visible wavelength pass through the earth’s atmosphere and can be useful in
light, infrared light, and ultraviolet. Imaging is done with the help of a system transmitting information to and from satellites in orbit. Hence, the
called an image forming an optical system. satellite dishes are made of metal as they reflect microwaves well.
Ray optics is also called geometrical optics. It is a branch of science  Microwaves of certain frequencies are absorbed by water. This property
that describes light propagation in terms of “rays”. of microwaves is useful n cooking. Water in the food absorbs
microwaves, which causes the water to heat up, therefore cooking the
Light and Its Optical Properties food.
 Microwave transmission is affected by wave effects such as refraction,
Light is a form of energy that is in the form of an electromagnetic wave reflection, interference, and diffraction.
and is almost everywhere around us. The visible light has wavelengths  Microwaves can pass through glass and plastic. This is the reason why
measuring between 400–700 nanometers. The Sun is the primary source of we use a plastic or glass container in a microwave oven and not metal
light by which plants utilize this to produce their energy. containers, as metal reflects microwaves.
In physics, the term light also refers to electromagnetic radiation of
different kinds of wavelengths, whether it is visible to the naked eye or not. X-Rays
Hence, by this, the gamma rays, microwaves, X-rays, and radio waves are We can define X-Rays or X-radiation as a form of electromagnetic
also types of light. Learn more by visiting the links below. radiation. They are powerful waves of electromagnetic energy. Most of them
have a wavelength ranging from 0.01 to 10 nanometers, corresponding to
Gamma rays frequencies in the range 3 × 1019 Hz to 3×1016 Hz and energies in the range
100 eV to 100 keV.
Gamma rays are high frequency (or shortest wavelength)
electromagnetic radiation and carry a lot of energy. They pass through most Who invented the X-Ray?
types of material. Only something hard, like a lead block or a thick concrete German physicist Wilhelm Röntgen is typically credited for the
block, can stop their transmission. discovery of X-Rays in 1895 because he was the first to comprehensively
study them, though he is not thought to be the first to have seen and perceived
Uses of Gamma Rays: their effects.
 Sterilize medical equipment
 Sterilize food (irradiated food) How Do X-Rays work?
 Used as tracers in medicine They are produced when high-velocity electrons collide with the metal
 Radio Therapy- In oncology, to kill cancerous cells plates, thereby giving the energy as the X-Rays and themselves absorbed by
 Gamma-Ray Astronomy the metal plate.
The X-Ray beam travels through the air and comes in contact with the
Microwaves body tissues, and produces an image on a metal film.
Microwaves are defined as electromagnetic radiations with a frequency Soft tissue like organs and skin cannot absorb the high-energy rays,
ranging between 300 MHz to 300 GHz. In contrast, the wavelength ranges and the beam passes through them.
Dense materials inside our bodies, like bones, absorb the radiation.
Radio Waves returns into a medium from which it was originated. The typical examples
Radio waves are usually produced by radio transmitters and can be for reflection of light include sound waves and water waves.
received by radio receivers. Radio waves having different frequencies contain Speed of light
various characteristics of propagation in the Earth’s atmosphere. The long The rate at which the light travels in free space is called the speed of light. For
waves get diffracted around different obstacles and follow the outline, whereas example, light travels 30% slower in water when compared to vacuum.
the short waves reflect the ionosphere and get back over the horizon of sky Refraction
waves. The propagation distance of both waves is limited to the visual horizon The bending of light when it passes from one medium to another is
as short wavelengths bend or diffract little and travel in a line of sight. called refraction. This property of refraction is used in a number of devices like
microscopes, magnifying lenses, corrective lenses, and so on. In this property,
when the light is transmitted through a medium, polarization of electrons takes
place which in turn reduces the speed of light, thus changing the direction of
light.

POWER OF LENS
The power of a Lens is one of the most interesting concepts in ray
optics. The detailed concept of this topic is given in the below article so that
learners can understand this chapter more effectively.
What Is Power of a Lens?
Simply put, the power of a lens in Ray Optics is its ability to bend light. The
greater the power of a lens, the greater its ability to refract light that passes
through it. For a convex lens, the converging ability is defined by power and in
a concave lens, the diverging ability.

Light exhibits various properties which are given below:

Reflection
Reflection is one of the primary properties of light. Reflection is nothing but the
images you see in the mirrors. Reflection is defined as the change in direction
of light at an interface in-between two different media so that the wave-front
 Do you notice the connection between the focal length and the bending 4. A stamp collector uses a converging lens with focal length 24 cm to
of the light ray? As the focal length decreases, the amount the light bends view a stamp 18 cm in front of the lens. (a) Where is the image located?
increases. Therefore, we can conclude that the power of a lens is inversely (b) What is the magnification?
proportional to the focal length of the lens. A short focal length basically 5. Suppose you have a concave lens of focal length f = 23.0 cm. An object
contributes to high optical power. of height 5.0 cm is placed 33.0 cm from the lens. Using the algebraic
Power of a Lens Formula method, determine: (a) the image distance; (b) the image height; (c) the
To find the power of a lens in Ray Optics, the following formula can be used. image magnification; (d) whether the image is real or virtual; and (e)
� whether the image is upright or inverted.
�= 6. Light rays travel from vacuum into a glass whose refractive index is 1.5.
� If the angle of incidence is 30°, calculate the angle of refraction inside
the glass.
If the focal length is given in metres (m), the power of the lens is measured in 7. A beam of light passing through a diverging lens of focal length 0.3m
Diopters (D), as in the unit of power of the lens is diopter. Another thing you appear to be focused at a distance 0.2m behind the lens. Find the
should keep in mind is that for a converging lens the optical power is positive position of the object.
and for a diverging lens, it is negative. 8. A person with myopia can see objects placed at a distance of 4m. If he
wants to see objects at a distance of 20m, what should be the focal
Optics Formulas length and power of the concave lens he must wear?
Following are the list of other optic formulas that are studied in optics:

Sample Problems
1. A diver shines a flashlight upward from beneath the water at a 42.5°
angle to the vertical. At what angle does light leave the water? Let’s
label the air as medium 1 and the water as medium 2. Then n1 = 1.00
for air, n2 = 1.33 for water, and θ2 = 42.5.
2. Rays of the Sun are seen to make a 31.0° angle to the vertical beneath
the water. At what angle above the horizon is the Sun?
3. The critical angle (for total internal reflection) for a certain liquid-air
surface is 47.7°. What is the index of refraction of the liquid?