Wave
Wave is a form of disturbance which travels onward due to repeated periodic motion of the medium particles. Energy is transferred during wave motion.
Types of wave
Mechanical wave: This type of wave motion requires material medium to propagate. For example ripples on water surface, vibration of a stretched string, sound wave, shock wave generated by a supersonic jet plane, seismic wave generated during earth quake.
Electromagnetic wave : Radiant energy like visible light, x-ray, infrared ray, micro wave etc. are simultaneous oscillations of electric and magnetic field. This type of wave can propagate without any material medium.
Transverse and longitudinal waves
Waves are again classified into two groups according to the direction of vibration of the medium particles with respect to the direction of wave propagation.
In transverse waves the particles vibrate in a direction perpendicular to the direction of wave propagation. Examples: vibration of stretched string, all electromagnetic waves
Crest
trough
In longitudinal waves the particles vibrate in the direction of wave propagation.
Rarefactions
Condensations
Wave parameter
Frequency (f):
The number of complete oscillations made in one second is called the frequency. The S.I. unit of frequency is Hertz (Hz)
Time period (T) :
Time taken by a particle to make one complete oscillation is called the time period.
Wavelength () :
The distance traveled by a wave during the time in which a particle makes one complete oscillation is called the wavelength.
Wave velocity/ phase velocity(v):
The distance moved by a wave per second is called its velocity.
v = f
Speed of light is vacuum is 3 x 108 m/s and the speed of sound wave in air is 340 m/s.
Electromagnetic waves
Wavelength of electromagnetic waves
Radiation Approximate wavelength
nm
Gamma rays 10-3
x-rays 10-1
Ultraviolet 100
Visible light 500
Infrared 104
Microwave 106
Radio 107 – 106
Light
Visible light is a very small fragment of the electromagnetic wave spectrum that creates sensation of vision in our eyes. The range of wavelength of the visible light is 360 nm (violet light) to 720 nm (red light). The wavelength of yellow light is about 589 nm. (1nm = 10-9 m)
Light rays and Beams
Ray
A ray is the direction or the path taken by light. Ordinarily it refers to a narrow stream of light energy. In diagrams rays are represented by lines with arrows on them.
Light ray
Beam:
A beam is a stream of light energy and may be represented by a number of light rays which may be converging or diverging.
(a) Parallel beam (b) Converging beam (c) Diverging beam
Reflection of light
The bouncing off of light or any wave at the face or boundary between two medium is called reflection.
The figure above illustrates the regular reflection of a light ray. MM` represents the surface of a plane mirror. AO is the incident ray i.e. the direction in which light falls on to the reflecting surface. O is the point of incidence; OB is the reflected ray and ON is the normal on the reflecting surface. The angle of incidence i and the angle of reflection r are made by AO and OB respectively with the normal NO.
Laws of reflection
The laws of reflection are stated as follows:
Law (1) The incident and the reflected rays are on the opposite sides of the normal at the point of incidence and all three are in the same plane.
Law(2) The angle of incidence is equal to the angle of refraction.
Diffuse reflection
Reflection from a coarse grainy surface is called diffuse reflection. In such case light from a single beam is reflected in various directions from the surface.
Image formation in a plane mirror
Light rays diverging out of the tip of a candle are reflected from the surface of the plane mirror MM`. Their extrapolations in back ward direction intersects at I. I is the position of the image of the tip of the candle. The eye sees the cone of rays E1IE2 seem to coming out of the Tip of the image I. however the AIB portion of the rays does not exist and hence the image is a virtual one.
Fig: lateral inversion of image Fig. formation of image in plane mirror
Another important property of the image formed by reflection is that it is laterally inverted, i.e. left becomes right and right, left. This is why is written as on the front hood of it. This is done for the drivers of the cars ahead of it who will see the ambulance in his rear view mirror and find the word in proper orientation-AMBULANCE.
Write down examples of four waves.
What type of waves are the following:
Earth quake, microwave, yellow light, X-ray, sound, ultraviolet (UV) ray.
Which of the following light is used for vision.
Earth quake, microwave, yellow light, X-ray, sound, ultraviolet (UV) ray, violet ray.
Give wave length of violet light, yellow light and red light.
What kind of wave light is?
What are the differences between light and sound?
What is reflection? What are the laws of reflection?
Describe regular and diffuse reflection.
Explain the formation of image by a plane mirror.
What type of image is formed by a plane mirror? Why?
Explain why emergency vehicles such as ambulance are often marked on the front hood with reversed lettering (
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