# Waves and Optics

1. May 7, 2005

### eutopia

The width of a slit is 19.3 mm. Light with a wavelength of 505 nm passes through the slit and falls on a screen that is located 48.7 cm away. In the diffraction pattern, find the width of the bright fringe that is next to the central bright fringe.

Assuming that the speed of sound is 340 m/s, how far from the amplifier should you sit to hear the electric guitar at the same time as a person 2.95×107 meters away in a spaceship will hear the guitar listening with headphones to a live radio transmission?

2. May 7, 2005

### The Bob

This one needs $$\frac{\lambda}{d} = \frac{x}{L}$$ when $$\lambda$$ is the wavelength, d is the diffration grating size, x is the fringe spacing and L is the distance the diffration grating is from the place of observation. Do you reckonise that equation at all or is it new to you???

Am I to assume that 2.95 x 107 means 2.95 x 107???

All you need to do is work out how long it will take for the sound to reach the spaceship (assuming that the speed of electromagnetic radation is 3 x 106 ms-1). Then you can use that time, with the speed of sound, to work out your distance.

3. May 7, 2005

### eutopia

hey thanks! no, i didn't know that equation, the first one for the waves. i was trying to find an equation for that problem and couldn't find one anywhere in my book.

im assuming the speed of electromagnetic radiation is 3e8, right? and it worked out too.. thanks!

4. May 7, 2005

### The Bob

Have you got the answers you wanted??? If so good, no problem and I was happy to help.

5. May 7, 2005

### eutopia

In Young's double slit experiment, 425 nm light gives a fourth-order bright fringe at a certain location on a flat screen. What is the longest wavelength of visible light that would produce a dark fringe at the same location? Assume that the range of visible wavelengths extends from 380 to 750 nm.

I did 425nm/4 times 3.5, but the computer says I'm wrong and I don't know why.

6. May 7, 2005

### eutopia

oh i got it! it says the LONGEST... so I had to divide by 2.5

7. May 8, 2005

### The Bob

So have you got the answers you wanted???

8. May 8, 2005

### eutopia

yup hehehe... silly me

9. May 8, 2005

Good good.