Single-slit diffraction IB DP Physics Study Notes - 2025 Syllabus
Single-slit diffraction IB DP Physics Study Notes
Single-slit diffraction IB DP Physics Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Physics syllabus with Students should understand
the condition for constructive interference as given by path difference = nλ
- the condition for destructive interference as given by path difference = (n +1/2)λ
Standard level and higher level: 5 hours
Additional higher level: 6 hours
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
Diffraction through a single-slit and around objects
∙If a wave meets a hole in a wall that is of comparable size to its wavelength, the wave will be bent through a process called diffraction.
∙If the aperture (hole, opening, etc.) is much larger than the wavelength, diffraction will be minimal to nonexistent.
FYI ∙
Diffraction is caused by objects within the medium that interact with the wave. It is not caused by two mediums and their boundary.
∙Christian Huygens explained the behavior of diffraction through his famous principle:
“Every point on a wavefront emits a spherical wavelet of the same velocity and wavelength as the original wave.”
∙Note that it is because of Huygen’s principle the waves can turn corners.
The reason waves can turn corners is that the incoming wave transmits a disturbance by causing the medium to vibrate.
∙And wherever the medium vibrates it becomes the center of a new wave front as illustrated to the right.
∙Note that the smaller the aperture b the more pronounced the diffraction effect.
FYI ∙
The aperture size must be of the order of a wavelength in order for diffraction to occur.
Path difference
∙This animation showing two coherent (in-phase and same frequency) wave sources S1 and S2 will show the following:
∙This animation showing two coherent wave sources S1 and S2 will show the following:
Diffraction through a single-slit
∙Huygen’s wavelets not only allow the wave to turn corners, they also interfere with each other.
EXAMPLE:
If light is diffracted by a circular hole, a planar cross-section of the interference looks like the picture below. What will the light look like head-on?
▶️Answer/Explanation
SOLUTION:
∙Picture the waveform of the previous slide in 2D
IB Physics Single-slit diffraction Exam Style Worked Out Questions
In two separate experiments monochromatic light is incident on a single slit. The diagrams show the diffraction patterns obtained on a screen far from the slit. In the top diagram the wavelength of light is \({\lambda _1}\) and the slit width is \({b_1}\). In the bottom diagram the wavelength of light is \({\lambda _2}\) and the slit width is \({b_2}\).
In each experiment the distance between the slit and the screen is the same. Which of the following may be deduced?
A. \(\frac{{{\lambda _1}}}{{{b_1}}} < \frac{{{\lambda _2}}}{{{b_2}}}\)
B. \(\frac{{{\lambda _1}}}{{{b_1}}} > \frac{{{\lambda _2}}}{{{b_2}}}\)
C. \({b_1} < {b_2}\)
D. \({\lambda _1} > {\lambda _2}\)
Answer/Explanation
Markscheme
A
Light is diffracted at a single slit. Which of the following graphs best represents how the intensity I of the diffracted light varies with the diffraction angle θ?
Answer/Explanation
Answer – C
High primary maxima, other maxima slowly decrease