Young's double slit experiment

In summary, for a Young's double slits experiment with a monochromatic light source of wavelength 700nm and a slit separation of 0.1mm, if 15 bright fringes are observed, the angle subtended by those fringes at the center of the double slit is 5.6°, which is the correct answer B. This is found by using the equation λ = y • d / (m • L) and solving for tanΘ, which gives 5.62° when multiplied by 2.
  • #1
libbytam
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Homework Statement


In a Young's double slits experiment, a monochromatic light source of wavelength 700nm is used and the separation of the slits is 0.1mm. If 15 bright fringes are observed, what is the angle subtended by those fringes at the centre of the double slit?
A. 6.0°
B. 5.6°
C. 5.2°
D. 4.8°

the correct answer is B, but why..??

Homework Equations


λ = y • d / (m • L)

3. The Attempt at a Solution

λ = 7 x 10^-7 m
y = fringe separation = ?
d = slit separation = 1 x 10^-4 m
m = order value = 15
L = distance from slit to screen = ?

I've drawn a triangle which represents the double slit experiment and I know the final step will be using tan Θ. There'll be only 7 bright fringes on the one side so m = 7 (not sure if it's correct or not...)
However, I've tried to get the equation with two unknowns (y and L).
I got: (7 x 10^-7) = (y)(1 x 10^-4) / (7)L
(4.9 x 10^-6)L = (1 x 10^-4)y
as tanΘ = y/L = (4.9 x 10^-6)/(1 x 10^-4) = 0.049
Θ = 2.81° (correct to 3 sig. fig.)

...which is obviously not the correct answer... so if it's multiplied by 2 , Θ = 2.81 x 2 = 5.62, which is answer B!?

Is there a better way? Can someone please help me out?
 
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  • #2
The angle subtended means the angle formed between the 7th fringes on both sides and the center of the slit, so, multiplying by two is indeed the correct way.
 
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1. What is Young's double slit experiment?

Young's double slit experiment is a classic experiment in physics that demonstrates the wave nature of light. It involves a light source, two small slits, and a screen. When light passes through the two slits, it diffracts and creates an interference pattern on the screen.

2. What does the double slit experiment prove?

The double slit experiment proves that light behaves like a wave, rather than a particle. The interference pattern created on the screen is only possible if light waves are interacting with each other, showing that light can exhibit wave-like properties.

3. Who discovered the double slit experiment?

The double slit experiment was first performed by English physicist Thomas Young in the early 1800s. He used this experiment to support the wave theory of light proposed by Christiaan Huygens.

4. What factors affect the interference pattern in the double slit experiment?

The interference pattern in the double slit experiment is affected by the wavelength of the light, the distance between the slits, and the distance between the slits and the screen. These factors determine the spacing and intensity of the interference fringes on the screen.

5. Can the double slit experiment be used to observe other wave-like phenomena?

Yes, the double slit experiment can be used to observe other wave-like phenomena, such as the diffraction of water waves and sound waves. It has also been adapted to demonstrate the wave-particle duality of matter, where particles such as electrons also exhibit wave-like properties.

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