- #1

Sarah0001

- 31

- 1

1. A white light shines vertically down on a horizontal CD ROM disc.

The disc is viewed by a teacher whose eye is a horizontal distance 0.50 m from the disc and 0.35 m vertically above its horizontal plane, Figure 1.2. A yellow light of wavelength 590 nm is observed due to first order diffraction.

Fig 1.2 Uploaded image

. (i) Deduce the spacing d between adjacent tracks of the CD ROM.

Answer: 720 nm,

angle subtended between incident and reflected ray is 55 degrees

2) relevant equations :

This below part is what I require help with.

(ii) The CD ROM is tilted, clockwise through an angle of 5 degrees . Determine the wavelength now observed.

3. My attempt at the solution :

wavelength = 720*10^-9 * sin 60

Worked solution: (uploaded)

I understand that the angle of incidence ray with mirror is now 95 degrees as opposed to 90,

so 95-55 = 40

so cos theta 1 = wavelength / d , theta 1 is 40, and thus sin theta 2 = wavelength / d , theta two must be 50 degrees by ( 180-90-40).

However I

The disc is viewed by a teacher whose eye is a horizontal distance 0.50 m from the disc and 0.35 m vertically above its horizontal plane, Figure 1.2. A yellow light of wavelength 590 nm is observed due to first order diffraction.

. (i) Deduce the spacing d between adjacent tracks of the CD ROM.

Answer: 720 nm,

angle subtended between incident and reflected ray is 55 degrees

2) relevant equations :

This below part is what I require help with.

(ii) The CD ROM is tilted, clockwise through an angle of 5 degrees . Determine the wavelength now observed.

3. My attempt at the solution :

wavelength = 720*10^-9 * sin 60

Worked solution: (uploaded)

I understand that the angle of incidence ray with mirror is now 95 degrees as opposed to 90,

so 95-55 = 40

so cos theta 1 = wavelength / d , theta 1 is 40, and thus sin theta 2 = wavelength / d , theta two must be 50 degrees by ( 180-90-40).

However I

__do not understand why 'sin5' is subtracted by sin 50 in the worked solution__s,__nor do I understand how cos ( 90 - 5) leads to sin (5), or cos(90 -x+5) = sin ( x -5) for that sake__

Also fundamentally I cannot understand why the worked solutionsAlso fundamentally I cannot understand why the worked solutions

__initially__finds the path difference to equal to (cosine A - Cosine B ) * slit separation (d)