Waves
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What do waves transfer?
They transfer energy without transferring matter.
What is a longitudinal wave? 2 examples
Vibrations are parallel to the direction the wave propagates(travels). Eg, sound and seismic P waves.
What is a transverse wave? 3 examples
Vibrations are at right angles to the direction of propagation. Examples: electromagnetic waves, water waves and seismic S waves.
Features of a wave? 4 and include units
Wavelength - Distance between 2 adjacent peaks or trough or, distance between 2 adjacent points of maximum compression / 2 adjacent points of minimum compression. Frequency - No. of complete waves that go past a point per unit time. (Hertz, Hz) 1Hz = 1 complete wave per second. Amplitude - Maximum particle displacement of the wave from the undisturbed position. (m. cm or mm) Wave speed - Distance travelled by the wave per unit time (ms-1) Depends on medium travelled through.
Relationship between wavelength and frequency? How to calculate wave speed?
If the wave is a constant speed, changing the wavelength also changes the frequency Wave speed: v = f x λ f = v / λ λ = v / f
What is the normal line? what is it used for?
Line at 90 degrees to the mirror. Angle of the rays is measured from here
What happens when you look at yourself in a plane mirror?
The image is laterally inverted, object is the same distance behind the mirror as it is infront, same size, upright
Why do plane mirrors produce virtual images?
When the reflected rays are extrapolated backwards, they appear to come to a point behind the mirror, tricking the eye to think the light started from the image.
What is reflection?
Incident light ray hits a mirror and is reflected off. Angle of incidence = angle of reflection.
What is refraction?
Change in direction of a light ray passing from one medium to another.
How does the mediums density affect the rays?
More dense, light bends towards the normal line. Less dense, light bends away from the normal line.
What is the principal focus of a convex lens?
The point where the parallel light rays all converge due to refraction.
What is the focal length?
Distance between the principle focus and the centre of the lens.
What is the principal axis?
The line of symmetry passing through the centre of the lens which the principal foci lie on.
What happens to the image when an object is placed two focal lengths away from a convex lens? 4 points
Image is diminished, inverted, closer to the lens than the object and it is real.
What happens to the image when an object is placed between one and two focal lengths away from a convex lens?
Image is enlarged, inverted, further from the lens than the object and it is real.
What is dispersion of light?
The refractive index of the glass or plastic prism is different for each colour of light. Causing each colour to be refracted by a different amount therefore separating (dispersion). Dispersion increases twice. When the light rays enter the prism and when they exit the prism. Refractive index of glass / plastic separates colours. exiting the prism, light colours bend away from (speed up by diff amounts) normal line at diff wave lengths separating further.
The seven colours from light dispersion in order of frequency and Wave length:
Frequency: Violet, indigo, blue, green, yellow, orange, red Wave length: Red, orange, yellow, green, blue, indigo, violet
What is a similarity among electromagnetic waves?
They travel at the same speed in a vacuum and aproximately the same in air.
What is the speed of electromagnetic waves in a vacuum?
3.0 x 10 to the power of 8 ms-1
Order the electromagnetic waves based on frequency and wave length: 7 each
Frequency: Gamma rays, xrays, ultraviolet rays, visible light, infrared rays, microwaves, radiowaves Wave length: Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, xrays, gamma rays
Applications of different electromagnetic waves:
Radiowaves - radar, radios and TV Microwaves - Satellite communication, cellphones, microwave ovens Infrared - TV remotes, thermal imaging Visible light - vision ultraviolet - detecting fake bank notes xrays - Medical and security scanning Gamma rays - Detection and treatment of cancer.
Harmful effects of electromagnetic radiation: 3 types of waves
Ultraviolet - Damage to surface cells (can cause skin cancer) Damage to the eyes possibly leading too cataracts and macular degeneration. Xrays and gamma rays - body cells can be permanently damaged or mutated.
How is sound produced?
Sound is produced in air by any vibrating object