The slit separation is increased. Outline one change observed on the screen.

Monochromatic light from two identical lamps arrives on a screen.

The intensity of light on the screen from each lamp separately is I₀.

On the axes, sketch a graph to show the variation with distance x on the screen of the intensity I of light on the screen.

In two different experiments, white light is passed through a single slit and then is either refracted through a prism or diffracted with a diffraction grating. The prism produces a band of colours from M to N. The diffraction grating produces a first order spectrum P to Q.

What are the colours observed at M and P?

Determine the width of one of the slits.

A beam of monochromatic light is incident normally on a diffraction grating. The grating spacing is d. The angles between the different orders are shown on the diagram.

What is the expression for the wavelength of light used?

A.   $\frac{d\text{sin}\alpha }{2}$

B.   $\frac{d\text{sin}\beta }{2}$

C.   d sin α

D.   d sin β

Monochromatic light of wavelength $\lambda$ in air is incident normally on a thin liquid film of refractive index $n$ that is suspended in air. The rays are shown at an angle to the normal for clarity.

What is the minimum thickness of the film so that the reflected light undergoes constructive interference?

A.  $\frac{\lambda }{4n}$

B.  $\frac{\lambda }{3n}$

C.  $\frac{\lambda }{2n}$

D.  $\frac{\lambda }{n}$

A transparent liquid film of refractive index 1.5 coats the outside of a glass lens of higher refractive index. The liquid film is used to eliminate reflection from the lens at wavelength λ in air.

What is the minimum thickness of the liquid film coating and the phase change at the liquid–glass interface?

A transparent liquid forms a parallel-sided thin film in air. The diagram shows a ray I incident on the upper air–film boundary at normal incidence (the rays are shown at an angle to the normal for clarity).

Reflections from the top and bottom surfaces of the film result in three rays J, K and L. Which of the rays has undergone a phase change of $\pi$ rad?

A. J only

B. J and L only

C. J and K only

D. J, K and L

Explain why zero intensity is observed at position A.

Predict whether reflected ray X undergoes a phase change.

Calculate the angular separation between the central peak and the missing peak in the double-slit interference intensity pattern. State your answer to an appropriate number of significant figures.

Light of wavelength λ is normally incident on a diffraction grating of spacing 3λ. What is the angle between the two second-order maxima?

A.  ${\sin }^{-1}\frac{2}{3}$

B.  ${\sin }^{-1}\frac{4}{3}$

C.  $2{\sin }^{-1}\frac{2}{3}$

D.  >90° so no second orders appear

State and explain the differences between the pattern on the screen due to the grating and the pattern due to the double slit.

Monochromatic light of wavelength λ in air is incident normally on a thin film of refractive index n. The film is surrounded by air. The intensity of the reflected light is a minimum. What is a possible thickness of the film?

A.     $\frac{\lambda }{4n}$

B.     $\frac{3\lambda }{4n}$

C.     $\frac{\lambda }{n}$

D.     $\frac{5\lambda }{4n}$

Light of wavelength λ is incident normally on a diffraction grating that has a slit separation of $\frac{7\lambda }{2}$. What is the greatest number of maxima that can be observed using this arrangement? 

A. 4 
B. 6 
C. 7 
D. 9

State the phase change when a ray is reflected at B.

Explain the condition for w that eliminates reflection for a particular light wavelength in air ${\lambda }_{\text{air}}$.

The separation of adjacent slits is d. Show that for the second-order diffraction maximum $2\lambda =d\sin \theta$.

calculate the smallest value of d that will result in destructive interference between ray X and ray Y.

The distance from the centre of the pattern to A is 4.1 x 10^–2 m. The distance from the screen to the slits is 7.0 m.

Calculate the width of each slit.

Calculate the frequency heard by the observer.

A beam of monochromatic light is incident on a diffraction grating of N lines per unit length. The angle between the first orders is θ₁.

What is the wavelength of the light?

A.     $\frac{\sin {\theta }_1}{N}$

B.     N sin θ₁

C.     N sin$\left(\frac{{\theta }_1}{2}\right)$

D.     $\frac{\sin \left(\frac{{\theta }_1}{2}\right)}{N}$

Deduce, in mm, the width of one slit.

Monochromatic light of wavelength 633 nm is normally incident on a diffraction grating. The diffraction maxima incident on a screen are detected and their angle θ to the central beam is determined. The graph shows the variation of sinθ with the order n of the maximum. The central order corresponds to n = 0.

Determine a mean value for the number of slits per millimetre of the grating.