29 A pattern of interference fringes is produced using a red laser, a double slit and a screen. The screen is 3.5m from the double slit. The light from the laser has a wavelength of 640 nm.
The pattern of fringes is shown.
bright
fringe
1
not to
scale
72 mm
What is the separation of the slits?
A 1.2 x 10 m B 1.6 x 10 m
C 3.1 x 10 m
D 3.3 x 10 m
(очC

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.