IB Physics HL C.3 practice question

Question 1

Paper 2Hard10 marks

In a laboratory, a laser illuminates both slits of a double-slit plate at normal incidence. The separation of adjacent bright fringes is measured on a screen parallel to the plate. A reference laser has wavelength $600\ \mathrm{nm}$ With the original plate and a screen distance of $1.20\ \mathrm{m}$ the measured fringe separation is $3.00\ \mathrm{mm}$

(a)

Show that the slit separation of the original plate is approximately $0.240\ \mathrm{mm}$

[2]

(b)

The screen is moved to a distance of $1.80\ \mathrm{m}$ with the original plate and reference laser unchanged. Determine the fringe separation.

[1]

(c)

A replacement plate is used with the reference laser and the screen at $1.80\ \mathrm{m}$ The measured fringe separation is $3.00\ \mathrm{mm}$ Determine the slit separation of the replacement plate.

[1]

(d)

The replacement plate is used with an unknown laser wavelength. The screen is at $1.20\ \mathrm{m}$ and the fringe separation is $2.40\ \mathrm{mm}$ Determine the wavelength of this laser.

[2]

(e)

In a further run, an unknown laser gives a fringe separation of $3.00\ \mathrm{mm}$ with the screen at $1.20\ \mathrm{m}$ but the identity of the slit plate used was not recorded. A technician claims that the laser wavelength is the same as that of the reference laser. Determine whether this claim is justified, supporting your answer quantitatively.

[4]