4Wave-2

Outcomes

• Pupils can draw diffraction patterns through "large" and "small" gaps
• Pupils can say whether diffraction will occur based on gap size and wavelength

Specification References

3.8 understand that waves can be diffracted when they pass an edge

3.9 understand that waves can be diffracted through gaps, and that the extent of diffraction depends on the wavelength and the physical dimension of the gap.

Starter

Recap wave basics from last lesson

Main Body of Lesson

When using the strobe on the ripple tank ensure that you warn pupils that the frequency of the strobe may trigger photosensitivie epilepsy.

• Use the ripple tank to observe reflection and refraction if you haven't already
• Use the ripple tank to observe diffraction, vary the separation to see the effect this has on the ammount of diffraction
• Pupils need to be able to draw the pattern through large and small gaps
• Pupils also need to know that diffraction is only very noticable when the gap is a similar size to the wavelength

There are some nice diagrams for this in Physics For You.

Plenary

Talk about radio and TV waves and why people can recieve radio but not TV when in the shadown of hills.

Additional Information

Safety/Hazards

In all work with flashing lights, teachers must be aware of any student suffering from photo-induced epilepsy. This condition is very rare. However, make sensitive inquiry of any known epileptic to see whether an attack has ever been associated with flashing lights. If so, the student could be invited to leave the lab or shield his/her eyes as deemed advisable. It is impracticable to avoid the hazardous frequency range (7 to 15 Hz) in these experiments.