Unjumble the key words from recent lessons, to find the title of today’s lesson

Homework – Write it down Your task this week is to teach your mom/dad/nan/grandad (or another adult) about diffraction. They’ll need to write a note in your planner to say you’ve done it!!

What were they? Diffraction refraction waves reflection wavelength frequency amplitude pitch transverse longitudinal Diffraction Today’s Lesson Title

Objectives To know that waves can be diffracted (knowledge) To be able to draw wave front diagrams showing diffraction (application) To be able to explain a scenario using the science you have learned (application & comprehension)

Present New Information Ripple tank demo with next 2 slides to show diffraction

What is diffraction? Diffraction is a property of all waves, which can be shown by water waves in a ripple tank. Here, the waves travel along until they reach a gap. The width of the gap is similar to the wavelength of the waves. The waves pass through the gap and spread out. This is diffraction. So, when radio waves travel past an obstacle or through a narrow gap, they bend or spread out due to diffraction.

How does wavelength affect diffraction? The amount of diffraction depends on how the wavelength compares with the size of the gap. What happens if the wavelength is much smaller than the width of the gap? In this case, only the edges of the wave front are diffracted. The amount of diffraction depends on wavelength. The longer the wavelength, the greater the diffraction.

Simulation http://www.physics.buffalo.edu/claw/Page11/ProjectCLAW-P11.html

Can radio waves travel through walls? Radio waves are not absorbed strongly by walls, which is why radio (and television) signals can be received indoors. Tall objects, like buildings and hills, can prevent radio waves travelling directly from a transmitter, but this is not always a problem. In some areas, the reflection of waves off other buildings or hills can actually lead to improved radio reception.

Mini-Review True or false…. Get your cards ready!!!

Diffraction is a property of longitudinal waves, which can be shown by water waves in a ripple tank.

The amount of diffraction depends on how the frequency compares with the size of the gap.

Tall objects, like buildings and hills, can prevent radio waves travelling directly from a transmitter, but this is not always a problem.

The amount of diffraction depends on wavelength.

Construct – complete the following diffraction diagrams

Let’s check the answers – who’s drawing?

Mini-review of objectives To know that waves can be diffracted (knowledge) To be able to draw wave front diagrams showing diffraction (application) To be able to explain a scenario using the science you have learned (application & comprehension)

Apply - How do radios work in hilly areas? In hilly areas there may not be a clear path between the transmitter and the radio, so how can a signal be received? You’re going to have to think about this now! Your task is on the next slide Teacher notes This image shows “before” and “after” scenes of a farmer tending a large flock of sheep in a remote valley and his efforts to get reception on his portable radio. Left: The “before” scene shows a farmer and his sheep struggling to get radio reception before the arrival of a new radio mast in this hilly area. The imminent arrival of the new mast is publicised by the newspaper headline on “The Sheep Guardian” which reads “NEW MAST TO BRING RADIO TO ALL”. Right: The “after” scene shows the happy farmer and his sheep after the arrival of a new radio mast, which means that they no longer have any problems getting radio reception. This time the headline on “The Sheep Guardian” reads “ALL WE HEAR IS RADIO BAA-BAA”. Note that the new mast is deliberately not included in this second scene, the inference being that it is in the area, probably on the other side of one of the hills. The image can be used to introduce the idea that radios can work in hilly areas, even when there is not a direct line between the transmitter and receiver. The question then is how does this work. This leads on to diffraction, which is explained and illustrated on the following slides.

Collect a worksheet that has this question on Apply to demonstrate Collect a worksheet that has this question on Radio waves have a wavelength that is around 10 times longer than a television wave. Your task is to explain why a house located in a valley can receive a radio signal, but not a television signal, using the science from today’s lesson. Success criteria An explanation of the answer using the key science from today’s lesson, and including the lesson key word diffraction A completed supporting diagram that is annotated

What did you miss and why? Key points: TV waves are shorter than radio waves The radio waves are roughly the same size as the hill/valley The radio waves are diffracted around the hill, and picked up by the antenna The TV signal is not diffracted and so goes over the hill Maximum diffraction occurs when wavelength ~ size of gap/object Did you get it right? Teacher notes This two-stage animation illustrates how wavelength effects diffraction. While viewing the animation, it should be stressed the longer wavelengths of radio waves allows diffraction to occur. 5 key points How many did you get? What did you miss and why?

HSW - When have I experienced diffraction? How can the teacher hear the band but not see them? Sound waves have a wavelength similar in size to the width of the doorway and so are diffracted as they pass through. Teacher notes This illustration shows a school band (called “INTER-FEAR-ANCE”) carrying out an after-school practice in the main hall. To illustrate that sound waves can travel around corners, the teacher in the corridor (on the far right of the scene) has his hands over his ears as he can hear the band before even reaching the doorway, but he cannot see them. Light waves have a much shorter wavelength than sound waves and so are not diffracted by the doorway. This means the band can be heard but not seen by the teacher in the corridor.

Plenary Activity – Write a sentence explaining how you used each of the thinking skills below during the lesson Application Comprehension Knowledge