RP 2: Investigation of interference effects to include the Young’s slit experiment and interference by a diffraction grating.

What is the method used in the double slit experiment to determine the wavelength of a laser? (4)

- Set up the apparatus in a darkened room with the laser, double slit, and screen.

- Measure the distance (D) from the slits to the screen using a metre ruler (starting at 0.500 m).

- Measure across multiple fringes using a ruler, divide by the number of fringes to calculate the fringe width w.

- Repeat the experiment at increasing values of D (e.g. 0.600 m to 1.500 m) and calculate the mean value of w for each D.

What equipment is needed for the double slit experiment? (4)

- Laser.

- Double slit.

- White screen.

- Metre ruler.

What does the setup for the double slit experiment look like? (3)

What is the independent variable in the double slit experiment? (1)

The independent variable is the distance from slits to screen (D).

What is the dependent variable in the double slit experiment? (1)

The dependent variable is the fringe width (w).

What are the controlled variables in the double slit experiment? (1)

The controlled variables are the wavelength of the laser and slit separation.

What graph is plotted in the double slit experiment? (1)

A graph of fringe width (w) against screen distance (D) is plotted.

How is the gradient of the graph used in the double slit experiment? (1)

The gradient of this graph is equal to the wavelength divided by the slit separation (λ/s).

How is the wavelength calculated from the double slit graph? (1)

Multiply the gradient by the slit separation to find the wavelength (λ = Gs).

What is one safety precaution in the double slit experiment? (1)

Ensure the laser is pointed away from people's eyes to prevent eye damage.

How can alignment be improved in the double slit experiment? (1)

Align the slit and screen perpendicular to the laser beam to reduce parallax error.

How can measurement accuracy be improved in the double slit experiment? (1)

Use a set square with the ruler for accurate alignment.

How can stability be improved in the double slit experiment? (1)

Ensure the screen and slits are steady and do not move during measurement.

What is the method used in the diffraction grating experiment to determine the wavelength of a laser? (4)

- Set up the laser and diffraction grating in a darkened room with a screen behind the grating.

- Measure the perpendicular distance (D) from the grating to the screen using a metre ruler.

- Measure the distance (h) from the central maximum to the first-order fringe (both sides) and calculate the mean. Do not use other fringes above the first-order as they are fainter and wider so the calculation is less accurate.

- Use the values of h and D to calculate the angle θ, then use the formula λ = d sin(θ)/n to find the wavelength.

What equipment is needed for the diffraction grating experiment? (4)

- Laser.

- Diffraction grating.

- White screen.

- Metre ruler.

What does the setup for the diffraction grating experiment look like? (3)

What is the independent variable in the diffraction grating experiment? (1)

The independent variable is the distance from grating to screen (D).

What is the dependent variable in the diffraction grating experiment? (1)

The dependent variable is the distance to the diffraction maxima (h).

What are the controlled variables in the diffraction grating experiment? (2)

- The controlled variables are the number of slits per metre (grating spacing).

- Another controlled variable is the wavelength of the laser.

How is the angle θ calculated in the diffraction grating method? (1)

The angle θ is calculated using arctangent of h/D.

How is the wavelength calculated in the diffraction grating method? (2)

- The wavelength λ is then found using λ = d sin(θ)/n.

- Where d is the slit spacing and n is the order of diffraction.

What is one safety precaution in the diffraction grating experiment? (1)

Ensure the laser is never pointed at anyone's eyes to prevent serious eye damage.

How can alignment be improved in the diffraction grating experiment? (1)

Use a set square with the ruler to ensure the screen and grating are perpendicular to the laser.

How can angular accuracy be improved in the diffraction grating experiment? (1)

Ensure the laser beam is aligned centrally with the grating to minimise angular errors.