Refraction Marcus Han 3O3 (10)

Refresh…  Refraction is the change in direction of a wave/ light ray when it enters an optically denser/lighter medium at an angle.

1. Microscope  Light bounces off the mirror, passes through the specimen on the stage and into the objective lenses. They refract of the light beams so that they travel straight through the microscope tube. When they reach the eyepiece lenses they are refracted into our eyes.

 Different colours of light are refracted more than others. This is known as “chromatic aberration”.  Chromatic: “pertaining to color or colors”  Aberration: (optics) “any disturbance of the rays of a pencil of light such that they can no longer be brought to a sharp focus or form a clear image”  To prevent this, most microscopes use more than one lens for the objective and the eyepiece.

2. Refractor telescope  There are 2 types of telescopes – the reflector telescope and the refractor telescope.

 The objective lens makes light rays converge at a focal point in the telescope to collect a bright image. It is then magnified to the size of a pupil and the eyepiece brings this bright image to the eye.  This magnification allows the image to take up a lot of space on the retina so we will be able to see distant objects very clearly.

3. SLR (Single Lens Reflex) Camera  When the shutter opens, light rays enter the lens.  An image formed by a single converging lens would be affected by aberrations like chromatic aberration.  By using several lenses made of different materials, each lens handles colors in a certain way to make the colours realign when the lenses are put together.

 The converging lens make the light rays converge at a point to form a bright image, which is exposed to film. The film makes a chemical record of the pattern of light, with loads of tiny light-sensitive grains, spread out in a chemical suspension on a strip of plastic. When exposed to light, they undergo a chemical reaction.

Shutter  Controls how long the film is exposed to the light.  Most SLR cameras use a focal plane shutter which consists of two "curtains" between the lens and the film. When a picture is taken, the first curtain slides open. After a while the second curtain slides in from the other side to stop the exposure.

 The curtains are controlled by a complicated set of gears, springs and switches.

4. Nuclear reactors (utilising Cherenkov radiation)  Named after Pavel Alekseyevich Cherenkov  When charged particles pass through an insulator at a constant speed greater than the speed of light in that medium,  They polarise the molecules of that medium, which quickly return to their ground states, causing immediate radiation.  This is called Cherenkov radiation and it causes the blue glow in nuclear reactors.

5. Phoropter  An instrument to measure a person’s refractive error and determine prescriptions for spectacles. The patient sits behind the phoropter, and looks through a pair of lenses. The optometrist changes lenses on the phoropter according to the patients feedback on which lenses give the best vision.  In a pair of spectacles/ a phoroptor the lenses compensate for refraction error by moving the blurred images of distant objects backward onto the retina.

References              h.gif h.gif  A9s.jpg A9s.jpg   /s1600-h/Advanced_Test_Reactor.jpg   Equipment/phoropter.htm