Examples of Total Internal Reflection Do Now Total internal reflection sheet

Lenses

Lenses You have two lenses on your bench, one that is thick in the middle (converging) and one that is thin in the middle (diverging). Try looking through them.

Converging and diverging lenses WHY?

Principal axis The straight line that goes through the centre of the lens at right angles to the lens surface

Principal focus Rays parallel to the principal axis, after being refracted by the lens, will all pass through a point on the principal axis called the principal focus.

Focal length The distance from the principal focus to the centre of the lens (denoted by the symbol f)

Finding the focal length - a quick practical Use the “distant light” method to show the students how to find the focal length. Give them a number of unmarked lenses that they have to find the focal length to.

Real and virtual images A real image is where the rays actually pass through the image and it can be projected and seen on a screen

Real and virtual images A virtual image is where no rays of light pass through, only their mathematical extensions. It cannot be displayed on a screen

Drawing ray diagrams

Drawing ray diagrams

Drawing ray diagrams

Drawing ray diagrams

Drawing ray diagrams You can check by drawing a ray backwards from the object parallel to the axis which has passed through the first principal focus.

Drawing ray diagrams

Do Now – 1. Stick in ray diagrams. 2. Draw the following table 3 Do Now – 1. Stick in ray diagrams. 2.Draw the following table 3. Fill in Object at Image at Size Orientation Nature Use >2F Image on a film close up 2F Photocopier Between 2F and F Projector F Spot light <F Magnifying glass

Now construct the following 5 diagrams An object at greater than 2F an object at 2F an object less than 2F an object at F an object at less than F

Image on a film (at infinity) Object at Image at Size Orientation Nature Use Infinity F Diminished Inverted Real Image on a film (at infinity) >2F Between F and 2F Image on a film (close up) 2F Same size Photocopier Between 2F and F Magnified Projector Spot light <F <F (on same side) Upright Virtual Magnifying glass

Virtual image

Let’s try it! – Investigating images practical on Wednesday

Diffraction

Diffraction definition Waves spread as they pass an obstacle or through an opening

Diffraction –diagrams are important Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave There is less diffraction when the opening is larger than the wavelength

Diffraction Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave

                                                                                                                                                                                                                                                                    Diffraction That’s why we can hear people around a wall but not see them!

                                                                                                                                                                                                                                                                    Do now stick in all you loose sheet and read the practical questions – this will be assessment you will need for the exam. pen, pencil ruler, rubber and protractor calculator

Learning today How images are formed Using the formulae for magnification and focal length – you are given these in the question

Investigating images practical

Let’s try some questions