Introduction of Electromagnetic waves,Types and uses of EM waves & Physical properties of EM waves & Laws

1. Nootan Physiotherapy College,
Visnagar.
Prepared By:
Dr. Nidhi Vedawala

3. Introduction
 EMR is in form of a wave consisting of regular sinusoidal
wave, under electric and magnetic field at right angle to
one another.

4. EM SPECTRUM
•The range of electromagnetic waves placed in order
of increasing frequency.
•It includes 7 types of EM radiation

5. Introduction
 R – RADIO WAVES – 0.1 mm to 100 km
 I – INFRA RED – 750nm to 4000 nm (0.4mm)
 V - VISIBLE LIGHT – 400 to 750 nm
 U – ULTRA VIOLET – 10 to 400 nm
 X – X-RAYS & GAMMA RAYS – 0.01 pm to 10 nm

6. Electromagnetic Spectrum
WAVELENGTH
RADIO INFRARED
MICROWAVE
VISIBLE
LIGHT ULTRAVIOLET
X-RAY
GAMMA RAY
RED YELLOW BLUE VIOLET
ORANGE GREEN INDIGO
WAVELENGTH
RADIO INFRARED
MICROWAVE
VISIBLE
LIGHT ULTRAVIOLET
X-RAY
GAMMA RAY
RED YELLOW BLUE VIOLET
ORANGE GREEN INDIGO
RED YELLOW BLUE VIOLET
ORANGE GREEN INDIGO

7. Types of EM
Radiation in
Spectrum

8. 1. Radio Waves
•Longest wavelength
•Lowest frequency
•Lowest energy in EM spectrum
•Uses:
 Radio broadcasting
 Satellite dish
 Television
 Cell phones

9. 2. Microwaves
• Are radio waves with very high frequency.
• Uses:
 Cooking in microwave ovens
 Cell phones
 Radar images (Doppler)

10. Types of EM Radiation
Microwaves
• Penetrate in to the
food and vibrate
water & fat molecules
to produce thermal
energy

11. 3. Infrared Waves (IR)
•Felt as heat energy or warmth
•Ex:
•Heat lamp

12. Types of EM Radiation
12
 Infrared Radiation (IR)
 Slightly lower energy than visible light
 Can raise the thermal energy (heat) of
objects

13. 4. Visible Light
 Visible Light
 Only part on EM
spectrum which can
be detected by human
eye.
 ROY G. BIV - colors
in order of increasing
frequency R O Y G. B I V
red orange yellow green blue indigo violet

14.  Human eye can detect EM energy in small portion of the
EM spectrum called the VISIBLE LIGHT REGION.
 Uses:
 Photosynthesis in plants

15. 5. Ultraviolet (UV)
• Main source of UV rays is sunlight.
• Produces Vitamin D
• Can kill micro-organism
• Insects can see UV light, human can’t
• Too much exposure lead to sun burn ,wrinkles , cancer as it can
cause damage to DNA
• It is used in hospitals to sterilize the surgical instruments & in
operation theater to kill bacteria.

16. Ultraviolet Radiation (UV)
 Slightly higher energy than visible light
 Types:
 UVA- 400nm-315nm
 UVB-315nm-280nm
 UVC-280nm-100nm

17. 6. X-Ray
•2nd highest frequency (high energy)
•X ray is generated by
•Rapid deceleration of fast rapid moving electrons
•Used in airports and hospitals
•Can cause cancer

18. X rays
 Higher energy than UV
 They can penetrate soft
tissue, but not bones.

19. 7. Gamma Ray
• Gamma rays are highest energy electromagnetic
waves.
• Shortest wavelength
• Highest frequency (most energy)
• Some radioactive substances & certain nuclear
reactions produce gamma rays.
• Because of their great penetrating ability , gamma
rays can cause serious illness.

20. Gamma rays
 How ever used in
controlled conditions
they are used to kill
cancerous cells
Radiation treatment using
radioactive cobalt-60.

22. Reflection
 It occurs when electromagnetic wave encounters a
medium which will not transmit it.
 In this case the ray is reflected back in the same plane.
 At the junction of two matter ray will change its velocity.
E.g It will travel from Air to glass, its wavelength reduces.
 Amount of reflection depends on
 Frequency of radiation
 Angle of incidence
 Nature of two media in contact

23.  Direction of reflection depends on
 Angle of incidence
 As the beam of radiation strike on a surface the wave
either
 Reflected or
 Penetrated
 More reflection – less penetration
 Amount of Radiation reflected or penetrated , depends on
 Angle of beam strike known as Angle of incidence
 Greater the angle of incidence- Greater the waves reflected
 Smaller the angle of incidence – lesser the waves reflected
 If angle if incidence is zero- greater transmission lesser
reflection

25. Parabolic Reflector
 In infrared and ultraviolet lamp a parabolic reflector is
normally used, avoids the danger of the concentration of
rays.
 It will collect all the rays travelling in an inappropriate
direction and reflect them from its surface so that they
eventually all emerge parallel.

26. Internal Reflection
 Internal reflection occurs when the angle of incidence of a
ray as it strike an interface between two media in such that
instead of being transmitted it is reflected.
 This happens at the angle of incidence above a critical
angle.

28. Refraction
 Refraction occurs when EMR are transmitted from one
medium to another with an angle of incidence greater than
zero.

29.  When radiation meets a boundary with a medium in which
it travels at a different velocity, its velocity will be altered
and it will refracted.
 Refraction causes a ray to deflected from its original
position.
 Amount of refraction is depends on
 Media
 Angle of incidence

30. Snell’s Law
 When rays passing less denser medium to high denser
medium , the ray is refracted towards normal.
 When rays passing more denser medium to less denser
medium , the ray is refracted away from the normal.

31.  Refraction is important when using Hydrotherapy as a
form of treatment, as the refraction of rays passing from
water to air makes the position of objects in the water
difficult to assess.
 The same is true when using water as a coupling medium
for ultrasound.

32. Interaction Of Radiation With Matter
 Reflected
 Transmitted (penetrate) – with refraction or without
refraction
 Absorption – energy of radiation is used or convert into
other form
32

33. Laws
 Grothus law
 Cosine law
 Inverse square law

34. Law Of Growthus
 Rays must be absorbed to produce an effect.
 Rays are absorbed at surface, disappears and produce
characteristic effect on site of absorption.
 A filter is a medium which will absorb some electromagnetic
waves whilst allowing others to pass.
 Window glass allows visible light and infrared rays to pass while
absorbing ultra violet to pass.
 Water absorbs infra red but allows visible and ultra violet to pass.
 X-rays are passed through soft tissues onto a photographic plate,
but are absorbed to a greater extent by bone.
 Cellophane absorbs short UV rays while allowing long ones to
pass.

35. The lambert’s Cosine Law:
 Intensity of rays at a surface varies with the cosine of the
angle between the incident ray and normal.
 Cosine of 90 = 0 (minimum)
 Cosine of 0 = 1 (maximum)

37. Inverse Square law
 “The intensity of rays from a point source varies inversely
with the square of the distance from the source.”
 I α 1/d2
 I1 / I2 = (D2)2 / (D1)2
 I1 = intensity of at D1 distance
 I2 = intensity of at D2 distance

40.  Arndt-Schulz Principle :
It states three things:
 Addition of a sub threshold quantity of energy will not
cause a demonstrable change;
 Addition of threshold & above quantity of energy will
stimulate the absorbing tissue to normal function.
 If too great a quantity of energy is absorbed then added
energy will prevent normal function or destroy tissue.