A diagram representing a double slit experiment using light is shown.
Which of the following best represents the expected pattern on the screen?
PHYSICS, M7 EQ-Bank 26
The diagram shows a light source, slits and a translucent screen arranged for an experiment on light. Light and dark bands form on the screen. The light has a wavelength of 590 nm. The diagram is not to scale.
- Explain how any one of the dark bands forms on the screen. (3 marks)
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- The distance between the centres of the double slit is 0.15 mm, and the distance between the double slit and the screen is 0.75 m.
- Calculate the distance on the screen from the centre of the central maximum to the centre of a second-order bright band. (3 marks)
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Show Worked Solution
a. → When light arrives at the double slit, it undergoes diffraction.
→ The two slits act as sources of secondary wavefronts and light travels from both slits to the screen.
→ When light from one slit travels any odd multiple of `(lambda)/(2)` more than light from the other slit to the screen, it is out of phase and destructive interference occurs. Here waves superimpose and cancel each other out, creating dark bands.
→ For example, the dark bands either side of the central maximum form where light from one slit travels `(lambda)/(2)` further than light from the other slit.
b. `d sin theta=m lambda`
| `0.15 xx10^(-3) sin theta` | `=2xx590 xx10^(-9)` | |
| `sin theta` | `=0.007867` |
→ Using trigonometry, `tan theta=(d)/(0.75)`, where `theta` is the angular separation of the second order bright band from the central maximum and `d` is the distance between the centre of the central maximum and the centre of the second order bright band.
→ As the angle, `theta` is small, the approximation `sin theta=tan theta` is valid:
| `tan theta` | `=(d)/(0.75)` | |
| `d` | `=0.007867 xx0.75` | |
| `=0.0059\ text{m}` |
PHYSICS M7 2022 HSC 27
A laser producing red light of wavelength 655 nm is directed onto double slits separated by a distance, `d=5.0 xx 10^{-5} \ text{m}`. A screen is placed behind the double slits.
- Newton proposed a model of light. Use a labelled sketch to show the pattern on the screen that would be expected from Newton's proposed model. (2 marks)
- When the laser light is turned on, a series of vertical bright lines are seen on the screen.
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- Calculate the angle, `\theta`, between the centre line and the bright line at `A`. (3 marks)
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- The laser is replaced with one producing green light of wavelength 520 nm.
- Explain the difference in the pattern that would be produced. (2 marks)
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Show Answers Only
a.
b. `theta=1.50^@`
c. Consider `d sin theta = m lambda :`
→ `sin theta prop lambda`
→ Using light with a shorter wavelength decreases the angular separation of bright fringes.
→ The bright lines will appear closer together.
Show Worked Solution
a.
Mean mark part (a) 53%.
b. Using `d sin theta=mlambda:`
| `5.0 xx10^(-5) sin theta` | `=2 xx6.55xx10^(-7)` |
| `sin theta` | `=(2 xx6.55xx10^(-7))/(5.0 xx10^(-5))` |
| `theta` | `=1.50^@` |
c. Consider `d sin theta = m lambda :`
→ `sin theta prop lambda`
→ Using light with a shorter wavelength decreases the angular separation of bright fringes.
→ The bright lines will appear closer together.
PHYSICS, M7 2020 HSC 1 MC
The diagram shows a model used to explain the refraction of light passing from medium `X` into medium `Y`.
Who proposed this model?
- Malus
- Planck
- Newton
- Huygens
PHYSICS, M7 2021 HSC 8 MC
Light from a point source is incident upon a circular metal disc, forming a shadow on a screen as shown. A bright spot is observed in the centre of the shadow.
The bright spot is caused by a combination of
- interference and refraction.
- refraction and polarisation.
- polarisation and diffraction.
- diffraction and interference.