A source of light having two wavelengths \(550 \mathrm{nm}\) and \(600 \mathrm{nm}\) of equal intensity is incident on a slit of width \(1.8 \mu \mathrm{m} .\) Find the separation of the \(m=1\) bright spots of the two wavelengths on a screen \(30.0 \mathrm{cm}\) away.

Short Answer

Expert verified
The separation between the m = 1 bright spots of the two wavelengths on the screen is approximately 8.7 mm.

Step by step solution

01

Write down the given information.

We are given the following information: - Wavelength of first light source (λ1) = 550 nm - Wavelength of second light source (λ2) = 600 nm - Width of the slit (a) = 1.8 μm - Distance from the slit to the screen (L) = 30 cm First, we need to convert all the given units to meters: - λ1 = 550 * 10^(-9) m - λ2 = 600 * 10^(-9) m - a = 1.8 * 10^(-6) m - L = 0.3 m
02

Apply the single-slit diffraction formula.

The single-slit diffraction formula for the first-order bright spots (m = 1) is given as: \(sin(\theta) \approx \frac{m \lambda}{a}\) For the first light source, let's call the angle θ1: \(sin(\theta_1) \approx \frac{1 \cdot (550 * 10^{-9})}{1.8 * 10^{-6}}\) For the second light source, let's call the angle θ2: \(sin(\theta_2) \approx \frac{1 \cdot (600 * 10^{-9})}{1.8 * 10^{-6}}\)
03

Solve for the angles θ1 and θ2.

Calculating the angles for both light sources: \(sin(\theta_1) \approx 0.3056\) Therefore, \(\theta_1 \approx 17.9°\) \(sin(\theta_2) \approx 0.3333\) Therefore, \(\theta_2 \approx 19.5°\)
04

Calculate the separation between the bright spots of both wavelengths.

Using the small-angle approximation, we can now calculate the separation between the first-order bright spots for the two wavelengths (Δy) using the formula: \(\Delta y = L \cdot tan(\theta_2 - \theta_1)\) Plugging in the values, we get: \(\Delta y = 0.3 \cdot tan(19.5° - 17.9°)\) \(\Delta y \approx 0.0087 \: m\)
05

Convert the separation to the required unit and write the final answer.

The separation between the first-order bright spots of the two wavelengths is 0.0087 meters. To convert it to millimeters, multiply by 1000: \(\Delta y \approx 8.7 \: mm\) Thus, the separation between the m = 1 bright spots of the two wavelengths on the screen is approximately 8.7 mm.

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