Physics Core Practical 6: Diffraction Gratings

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Questions and Answers

What does the variable 'd' represent in the diffraction grating equation?

The angle between the normal and the maxima

The order of the diffraction pattern

The distance between the slits (correct)

The wavelength of the laser light

Which wavelength is typically accepted for a standard school red laser?

635 nm (correct)

700 nm

650 nm

600 nm

What is the primary purpose of using a set square in the experiment?

To calculate the mean wavelength of the laser light

To increase the number of slits per meter

To avoid parallax error in fringe width measurement (correct)

To measure the distance from the slits to the screen

What effect does using a grating with more lines per mm have on the experiment?

Results in greater values of h Signup and view all the answers

How is the angle θ in the diffraction grating equation calculated?

Using trigonometry based on measurements of h and D Signup and view all the answers

What is the aim of the experiment involving diffraction gratings?

To find the wavelength of light Signup and view all the answers

Which variable is considered the independent variable in this experiment?

Distance between maxima Signup and view all the answers

Which piece of equipment has the highest resolution in this experiment?

Vernier Callipers Signup and view all the answers

What should be done to ensure the laser beam passes perpendicularly through the diffraction grating?

Use a set square Signup and view all the answers

What is measured after identifying the zero-order maximum?

The distance to the first-order maxima Signup and view all the answers

What action should be taken if the room is not darkened during the experiment?

The results may be inaccurate Signup and view all the answers

How should the mean of the two measurements of h be calculated?

Add the values and divide by two Signup and view all the answers

What should be done after measuring distance h for increasing orders?

Use a diffraction grating with a different number of slits per mm Signup and view all the answers

What method can help reduce percentage uncertainty in measurements of fringe spacing?

Using a Vernier scale for recording distances Signup and view all the answers

How can increasing the distance D from the grating to the screen affect the experiment?

It increases fringe separation but may decrease intensity Signup and view all the answers

What is a safety consideration when using lasers in the described experiment?

Ensure the laser output does not exceed 1 mW Signup and view all the answers

Which of the following steps is recommended to improve visibility of interference fringes?

Operating in a darkened room Signup and view all the answers

Why is it recommended to take multiple measurements of w and h?

To account for subjective variations in readings Signup and view all the answers

What is a possible consequence of removing reflective surfaces from the room during the experiment?

Prevention of unintended reflections into eyes Signup and view all the answers

When calculating the mean wavelength of laser light, what additional factor should be considered?

The standard deviation of measurements Signup and view all the answers

In an interference pattern experiment, what could lead to subjective results in fringe spacing measurements?

Lighting conditions affecting visibility Signup and view all the answers

Study Notes

Core Practical 6: Investigating Diffraction Gratings

Aim: To find the wavelength of light using a diffraction grating.
Independent variable: Distance between maxima (h).
Dependent variable: Angle (θ) between the normal and each order (n=1,2,3...).
Control variables: Distance between slits and screen (D), laser wavelength (λ), slit separation (d).
Apparatus and Purpose:
- Laser: Source of monochromatic light.
- Single slit: Focuses the beam.
- Double slit (optional): Diffracts the beam into two coherent light sources.
- Diffraction grating: Diffracts the beam into multiple coherent light sources.
- Metre ruler: To measure the distance between slits and screen (D).
- Vernier calipers: To measure fringe width (w) and slit separation (if not quoted).
- Retort stand: Supports laser and slits at the same height.
- White screen: Projects the interference pattern.
- Set square: Aligns components to a normal.
- Resolution: Metre ruler=1mm, Vernier Callipers = 0.01 mm

Method

Setup apparatus with diffraction grating at normal incidence to laser beam.
Measure distance between grating and screen (D = 1.0 m).
Identify the zero-order maximum (central beam).
Measure the distance (h) to the first-order maxima (n=1,n=2).
Calculate the mean h.
Measure h for increasing orders.
Repeat for a grating with a different number of slits/mm.
Use the equation tanθ = h/D to calculate θ.

Analysing the Results

The grating equation is ηλ = d sin θ.
Variables:
- η = order of the diffraction pattern
- λ = wavelength of laser light
- d = distance between slits
- θ = angle between normal and maxima
Calculate the mean wavelength of laser light.
Compare with accepted value (e.g., 635nm).
Calculate percentage uncertainty.

Evaluating the Experiment

Systematic errors: Ensure use of set square to avoid parallax error & use appropriate equipment resolution.
Random errors: Multiple measurements & averaging to reduce variability.
Safety considerations: Use appropriate laser safety precautions (e.g., use class 2 lasers, avoid shining laser into eyes).

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Description

This quiz investigates the process of determining the wavelength of light using a diffraction grating. It covers the setup, variables, and apparatus needed for the experiment, focusing on the relationship between distance and angle in diffraction patterns. Test your understanding of the concepts involved in this practical exploration of wave behavior.