Presentation on theme: "ELECTROMAGNETIC WAVES Name given to a range of waves having different wavelengths, frequencies and energies but some common properties All are propagated."— Presentation transcript:
ELECTROMAGNETIC WAVES Name given to a range of waves having different wavelengths, frequencies and energies but some common properties All are propagated by varying electric and magnetic fields which oscillate at right angles to one another and also to the direction of propagation of the wave All travel with the same constant speed in air or a vacuum…the speed of light…3.0x10 8 ms-1 All are unaffected by external electric and magnetic fields All are transverse waves All can undergo reflection, refraction, diffraction and interference All travel in straight lines in a vacuum or air or other medium All can be plane polarized All are progressive waves but can produce stationary waves under suitable circumstances The intensity of each varies inversely as the square of the linear distance from a point source
Electromagnetic spectrum is divided into the following range with specific range of 300nm (violet light) to 750nm (red light) Light has a wave-particle nature: Wave nature supported by the young double slit experiment that light can be Diffracted and interference can occur and The Photoelectric effect ( instantaneous emission of electrons from the surfaces of certain material when exposed to E.M. radiation above a certain frequency
Light Is a form of energy that has a particle and wave nature
Light travels in straight lines Its travel is represented by a ray A ray is a straight line a with an arrow showing the direction of travel A ray A group of rays represent a beam of light A beam
There are three main types of beams of light: Parallel beams Convergent beams Divergent beams Use your dictionary to write down the meanings of 1)Parallel ______________________________ 2)Convergent ___________________________ 3)Divergent ____________________________
A torch light creates a divergent beam, attempt to draw a beam of light from the torch light to show a divergent beam using the diagram below. Example: Is it? or Headlights on a car creates parallel beams, attempt to draw a beam of light to show a parallel beam using the diagram below A magnifying glass creates convergent beams, attempt to draw a beam of light to show a convergent beam using the diagram below
Luminous versus non-luminous If you are given the definition that luminous objects produce it own light and non- luminous objects reflect light, make a list of at least five objects that are luminous and non- luminous objects Luminous objectsNon luminous objects
And you are given the definition that: Transparent objects allow all light to pas through it Translucent objects allow some light to pass through it Opaque objects do not allow any light to pass through it Complete the table below with at least five items you see daily Transparent objects TranslucentOpaque GlassFrosted glassA wall
SHADOWS Are formed when an opaque object is placed in front of the path of light.
Shadows can be formed using Using a point source – which is a small light source such as a torch light Or an extended source – which is a large light source such as the sun
Solar eclipse When the moon passes between the sun and the Earth The moon fully or partially covers the view of the sun from the Earth The partially covered view is the area of the penumbra The fully covered view is the area of the umbra.
Total Solar Eclipse: The observer is inside the Moon's umbra. The Moon completely covers the Sun. Partial Solar Eclipse: The observer is inside the Moon's penumbra. Only see part of the Sun covered by the Moon. Annular Eclipse: The Moon is at or near apogee, and so is too small to cover the Sun. The Moon's umbra does not touch the Earth, so observer's in the shadow path see the Sun as a ring ("annulus") TO DO: Label on the diagram where you would be if you were seeing an Annular eclipse
Lunar Eclipse A lunar eclipse occurs when the moon passes behind the Earth and is blocked by Earth (the Earth acts as the opaque object) TO DO: Draw a diagram of the Sun, Earth and Moon in a lunar eclipse position
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