Question

7)

Higher energy photons can disrupt the bonds of your DNA, which can result in cancer. Based on this fact, which of the following should you avoid?

1. Radiowaves,withawavelengthof~1m

2. Microwaves, with wavelengths of ~ 1cm

3. Infrared waves, with a wavelength of ~1x10-6m

4. Gamma rays, with wavelengths of ~1x10-10m

In a double slit experiment, at a certain point on the screen, the waves coming from one slit will have traveled half a wavelength more than the waves coming from the other slit. At this point on the screen you will see

1. Abrightspot

2. A dark spot

3. A lit spot, but it won’t be the brightest one in the pattern

4. We need to know the wavelength

Answer 1

A.We know that Energy=(hc)/(wavelength in meters) where h is planck's constant and c is the speed of light.

We can find the energy of photons of each of the following types of radiation using this formula,

1. Radiowaves

E=(hc)/1=1.989x10-25

2.Microwaves

E=(hc)/(1x10-2)=1.989x10-23

3. Infrared waves

E=(hc)/(1x10-6)=1.989x10-19

4. Gamma Rays

E=(hc)/(1x10-10)=1.989x10-15

From this we observe that gamma rays have the highest energy and must be avoided.

B. In Young's Double Slit Experiment we deal with the wave nature of light. If it wasn't so we would simply see two lines on the screen. So when light is considered as waves, the two slits act as seperate sources and light from both these sources intefere. They may cause constructive or destructive interference. Pure constructive interference is when the crest falls on a crest and trough falls on trough. This happens when the light from both sources are in phase. Pure destructive interference occurs when crests fall on trough. This happens when identical waves are exactly out of phase, or shifted by half wavelength. As per the given question, the wavelength of one of the sources is shifted by half a wavelength. Hence pure destructive interference occurs and we see A DARK SPOT at this point.