Both Light and Sound Have Oscillating Waves
|
Velocity |
Travels Through Vacuum? |
Wavelength |
Frequency |
| Light |
186,000 miles/sec
(300,000 km/sec)
in vacuum |
Yes |
400-700 nm |
4 X 10^14
to 7 X 10 ^14
cycles/sec |
| Sound |
About 700 mph
(about 340 m/sec)
(1 mile per 5 seconds)
in air |
No |
.02 to 20 meters |
20-20,000 cycles/sec |
- Sound and light are waves in which the amplitude oscillates with time
- For pure tones or colors the oscillation is a sine wave with a fixed wavelength and frequency
- The wavelength is the distance between 2 peaks of the wave
A Snellen chart is an eye chart used by eye care professionals and others to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862
The traditional Snellen chart is printed with eleven lines of block letters. The first line consists of one very large letter, which may be one of several letters, for example E, H, N, or A. Subsequent rows have increasing numbers of letters that decrease in size. A patient taking the test covers one eye, and reads aloud the letters of each row, beginning at the top. The smallest row that can be read accurately indicates the patient’s visual acuity in that eye.
