1. A soap bubble (n= 1.35) is floating in air. If the thickness of the bubble wa
ID: 1649883 • Letter: 1
Question
1. A soap bubble (n= 1.35) is floating in air. If the thickness of the bubble wall is 300nm which of the following wavelengths of visible light is strongly reflected?
2. A ray of light is incident on a liquid to glass interface at an angle of 35 degrees. Indices of refraction for the liquid and glass are respectively 1.63 and 1.52. What is the angle of refraction for the ray moving through the glass?
3. An electron (charge- 1.6 x 10-19 C) moves on a path perpendicular to the direction of a uniform electric field of strength 3.0 N/C. How much work is done on the electron as it moves 15 cm?
4. A ray of light strikes a think sheet of glass (n=1.5) at an angle of 25 degrees with the normal. Find the angle of the ray refracted off the glass surface with respect to the normal.
Explanation / Answer
1)
2t = (m+1/2)/n
= 2tn/(m+1/2).............m = 1 for air
= 2(300)(1.35)/(1+.5)
= 540 nm
2)According to Snell's Law
sin i/ sin r = 1.52/1.63
sin r = sin i *(1.63/1.52) = (sin 35)*(1.63/1.52) = 0.615
r = sin-1 0.615 = 37.96 degrees
3)
charge q= -1.6 X 10^-19 C
Electric field = E = 3 N/C
Force F on electron = qE = -4.8 x 10^-19 Newtons
Distance moved = s= 15 cm = 0.15 m
We have,
Work done = Fscos
= 4.8 x 10^-19 x 0.15 x cos(90) (as the path of electron is perpendicular to the force on it)
= 0
Therefore Work Done on electron is 0
4) According to Snell's law
sin i/ sin r = 1.5
sin r = sin i / 1.5 = (sin 25)/1.5= 0.2817
r = sin-10.2817 =16.36 degrees
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