Light and EM spectrum (5) Flashcards
What is the law of reflection?
The angle of incidence = the angle of reflection.
What is total internal reflection?
When a wave travels from a more dense to a less dense medium, it can be refracted, pass along the surface or be reflected. When the angle of incidence is less than the critical angle, most light is refracted and some reflected. When the angle of incidence is equal to the critical angle, the wave passes along the surface and some is reflected. Finally, when it is larger than the critical angle, the wave is all reflected.
What is the difference between specular and diffuse reflection?
Specular:
Waves are reflected in a single direction by a smooth surface creating a clear image.
Diffuse:
Waves are reflected by a rough surface and in different directions (the normal is different for each incident ray). An unclear image is produced.
How does colour get to our eyes?
White light (ROYGBIV) is shone onto an object. If the colour of the object is blue, it will absorb all colours except blue which it will reflect. This is because all the colours have different wavelengths.
How do filters work.
Filters absorb every wavelength except the wavelength of one colour which it transmits. If you look at a red object through a blue filter, it will appear black as the red wavelength is absorbed by the filter.
What does the power of a lens rely on?
The focal length (distance between the centre of the lens to the focus) and the shape of the lens. The shorter the focal length and the more curved the lens, the more powerful the lens.
What image do diverging lenses form?
Virtual (light rays do not meet at a point and image cannot be captured on a screen), right way up and diminished.
What images do converging lenses form?
Object 2 focal points away will produce a real (light rays meet and can be captured on a screen), inverted and same size image.
Object between 2 and 1 focal point away will produce a real, inverted and magnified image.
Object 1 or less focal points away will produce a virtual, right way up and magnified image.
What are electromagnetic waves?
Transverse waves that travel at the same speed in a vacuum. They are in the order of, radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays increasing in frequency and decreasing in wavelength. They transfer energy, e.g. infrared waves transfer energy from thermal stores in a heater to the observer.
How are EM waves harmful?
The relative danger of EM waves increases as frequency increases. Excessive exposure to:
Microwaves can lead to internal heating of body cells.
Infrared can lead to skin burns.
UV can lead to damage to cell surface and eyes leading to skin cancer and eye conditions.
X-rays and gamma rays can lead to mutation or damage to cells in the body.
What are some uses of EM waves?
Radio waves - broadcasting and communications (long wavelengths can bend around curved surfaces so signals can be received from far away) and satellite transmissions.
Microwaves - communications and satellite transmissions (pass easily through atmosphere) and cooking (waves are absorbed by water molecules which heat up and transfer energy to food)
Infrared - cooking, thermal imaging (IR is given out by hot objects which can be detected by cameras which can turn it into an electrical signal which can be displayed on a screen) and transferring information (remote to TV or transferring files from one device to another).
Visible light - photography, vision and illumination.
Ultraviolet - security marking, fluorescent lamps, detecting forged bank notes (all of which absorb UV and emit visible light) and disinfecting water (UV kills bacteria).
X-rays - airport security scanners and medical x-rays (transmitted by flesh and absorbed by bone).
Gamma rays - sterilising food and medical equipment, detection of cancer and its treatment.
