P14: Light Flashcards
properties
convex lens
- focus light inwards (CONVERGING)
- used for magnifying glass/binoculars
- corrects longsightedness - focuses focus on retina
properties
concave lenses
- spread light outwards (diverging)
- correct short sightedness , as light is focused in FRONT of retina so spread light out to focus on retina
magnification ?
image height/object height
which colour has shortest/longest wavelength/frequncy?
RED - Longest wavelength/ lowest frequency
VIOLET - shortest wavelength/ highest frequency
specular reflection?
reflection from smooth surface in a single direction (shiny appearance)
( angle of reflection= angle of incidence)
diffuse reflection?
reflection from rough surface causes scattering
- when light scatters, leaves surface in all direction (causes matt appearance)
how can white light be speperated into all its colours?
- pass it through a prism
- light will refract
- violet refract most (highest frequ) and red refract least
- each colour has different wavelength , so refracts differently creating a spectrum
how do colour filters work?
work by absorbing certain wavelengths and transmitting other wavelengths
e.g if white light passes through red filter, red is transmittted , others are absorbed
how are colours of opaque object determined?
determined by which wavelengths of light are more strongly reflected
- wavelengths that are not reflected are absorbed - appear BLACK
e.g white light upon green surface will only have green light reflected
An object will appear white if ..
all wavelengths are reflected equally
an object will appear transparent if ..
all the light is TRANSMITTED, and only small amount is reflected and absorbed
difference between transparent object and translucent ?
Transparent objects transmit all light that enters the object , without absorbtion.
Translucent objects let light pass through them, but light is scattered/refracted
what is a black body?
an object that absorbs all the radiation it recieves (doesnt transmit/reflect any)
- emits all types of radiation
the hotter the body…
- the greater amount of radiation released per second (more powerful)
- the greater amount of high frequency radiation released (x rays)
how is a body kept at constant temperature?
the body absorbs radiation at the same rate as emitting it
- initially absorbs more radiation than it emits
- as it gets hotter, it emits more radiation
- soon, it will emit the same it absorbs
how to increase/decrease temperature of body?
INCREASES : absorbs more energy that it emitts
DECREASE: energy is released faster than it absorbs
how is temperature on Earth kept at a balance?
- earth recieves most thermal enrgy from sun
- at same time, Earth emits its own thermal radiation, with slightly longer wavelength (low frequ - less energy) than the radiation recieved
- greenhouse gases absorb /reflect back longer wavelength IR from earth - preventing it escaping to space
what contributes to the greenhouse effect?
the rate of absorbtion/emmission of radiation on Earth
- some radiation is reflected back to space
- some radiation is absorbed by earth or absorbed by greenhouse gases and re- emmitted to earth
what is focal length and what factors determine this length?
the distance between the centre of lens to focal point
- material lens is made from
- shape of lens
what happens to focal point if lens is more curved?
moves closer to lens
- more curved it is, refracted at a greater angle
what is meant by
virtual image?
- cannot be projected onto a screen
- appears behind lens
- only seen from looking through lens
what colour is best and worst absorber/emitter of radiation
best : black
worst : shiny
