---
title: "A student is investigating the properties of a horizontal soap film suspended in a circular frame in air (\\(n_{air} = 1.0\\)). The index of refraction of the soap solution is \\(n_{film} = 1.33\\). The student wishes to experimentally determine the uniform thickness \\(t\\) of the film.  The student has access to the following equipment: – A tunable laser that emits a narrow beam of monochromatic light of any selected frequency \\(f\\) – A light intensity sensor – Standard laboratory equipment (stands, clamps, metersticks, etc.)"
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url: "https://nerd-notes.com/ubq/117733/"
date_modified: "2026-08-04T07:54:12+00:00"
---

# A student is investigating the properties of a horizontal soap film suspended in a circular frame in air (\(n_{air} = 1.0\)). The index of refraction of the soap solution is \(n_{film} = 1.33\). The student wishes to experimentally determine the uniform thickness \(t\) of the film.

The student has access to the following equipment:
– A tunable laser that emits a narrow beam of monochromatic light of any selected frequency \(f\)
– A light intensity sensor
– Standard laboratory equipment (stands, clamps, metersticks, etc.)

A student is investigating the properties of a horizontal soap film suspended in a circular frame in air (\(n_{air} = 1.0\)). The index of refraction of the soap solution is \(n_{film} = 1.33\). The student wishes to experimentally determine the uniform thickness \(t\) of the film.

The student has access to the following equipment:
- A tunable laser that emits a narrow beam of monochromatic light of any selected frequency \(f\)
- A light intensity sensor
- Standard laboratory equipment (stands, clamps, metersticks, etc.)

**Part a)**  *(3 points)*

**Part b)**  *(3 points)*

**Part c)** The student performs the experiment and records the frequencies that produce a minimum reflected intensity, starting from the lowest frequency observed. The student assigns integer values \(m = 1, 2, 3, 4\) to these consecutive minimums. The data are shown in the table below. | Minimum Order \(m\) | Frequency \(f\) (\(\times 10^{14} \text{ Hz}\)) | | :---: | :---: | | 1 | 4.5 | | 2 | 9.0 | | 3 | 13.5 | | 4 | 18.0 | *(4 points)*

**Part d)** Instead of a soap film suspended in air, the student creates the same soap film (\(n_{film} = 1.33\)) with thickness \(t\) resting completely flat on top of a solid piece of transparent glass (\(n_{glass} = 1.50\)). The tunable laser is again directed downwards at the top surface of the film. **Predict** whether the specific frequencies \(f\) measured in Part C will now produce a maximum (constructive interference), a minimum (destructive interference), or neither in the reflected light. - [ ] Maximum (Constructive Interference) - [ ] Minimum (Destructive Interference) - [ ] Neither **Justify** your prediction using physical principles. *(2 points)*


*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117733/*