Diffraction (CIE A Level Physics)

White light is passed through a single narrow slit and illuminates a screen. 

Describe the pattern observed on the screen.

Blue light from a laser is now passed through a single narrow slit, as shown in Fig 1.1. A pattern of bright and dark regions can be observed on the screen which is placed several metres beyond the slit. 

Fig. 1.1

Describe the effect on the diffraction pattern if the width of the narrow slit is decreased.

With the original slit width, state and explain the effect on the width of the fringes on the diffraction pattern if the blue light is replaced with a red light of the same intensity. 

The intensity graph for the diffracted blue light is shown in Fig 1.2. 

Fig. 1.2

On the axes shown in Fig 1.2, sketch the intensity graph for the laser emitting red light.

A beam of monochromatic light is incident upon two slits. The distance between the slits is d as shown in Fig 1.1.

Fig 1.1

A series of bright and dark fringes appear on the screen. Explain how a bright fringe is formed.

If the wavelength of the incident light is halved and the distance between the slits is doubled, outline the effect on the separation of the fringes of the interference pattern.

One of the slits is covered so it emits no light.

Describe how this changes the pattern's appearance and the intensities observed on the screen.

Define diffraction.

The diagram shows a student in a room with an open door and a television in the next room. 

The student can hear the sound of the television, but cannot see the picture coming from it. 

Explain why this is the case. 

Explain what would happen in terms of diffraction of the sound waves, if the student's room mate partially closed the door.