LIGHT & OPTICS EXPERIMENTS

THE PHYSICS SUPERMARKET

  1. The Eye
  2. The Plane Mirror
  3. Multiple Images in Plane Mirrors
  4. Images formed by Lenses
  5. Images formed by Curved Mirrors
  6. Ray Tracing
  7. The Lens Formula
  8. Refraction
  9. Total Internal Reflection
  10. The Convex Lens
  1. The Eye part 2
  2. Fire in Diamonds
  3. The Rainbow
  4. The Magnifying Glass
  5. The Compound Microscope
  6. Telescopes
  7. The SLR camera
  8. Colour Filtration
  9. Colour Photography

1. The Eye

Students investigate how the Eye locates images and the optical illusions that occur if light changes dirctions after leaving the source. Apparent size is related to the angle subtended at the eye by the an object. Why objects are seen to have colour and fatigue of the eyes ability to sense the same colour are investigated. Lastly, students find their blind spot when one eye is open.

Ray/light box kit, Large piece of matt black paper or material, Red, white, yellow, green and blue squares of cardboard, Red filter, Spectroscope    Top

   

2. The Plane Mirror

Students investigate the relection of light off a plane mirror. They use their findings to locate the image formed by a plane mirror. They predict the minimum sized mirror that will just enable the whole face to be seen as the image. This is checked with a plane mirror a a piece of a paper with a window cut in it to size.

Light/Ray box, Plane mirror from ray box kit, Protractor, 30 cm ruler, Plane mirror with dimensions greater than half the width and height of the face. A mirror tile is suitable, Piece of paper as big as the mirror, Scissors  Top


3. Multiple Images in Plane Mirrors

Students set up two plane mirrors touching at one edge and vary the angle between them. They find the relationship between he number of images formed and the angle between the mirrors.

2 plane mirrors from the Ray/light box kit  Top


4. Images formed by Lenses

Students investigate the real and virtual images formed by concave and convex lenses. The method of parallax to locate images is first developed using real images formed by a convex lens and then proven to be true by projecting the images onto a screen. The position of the object is changed and the effect on the nature, position, size and orientation is investigated. Parallax is then used to locate virtual images formed by convex and concave lenses.

10 cm focal length convex lens and lens holder, 10 cm focal length concave lens, Candle and screen, A block of wood with a large thick nail that protrudes above the lens when in the holder or the base and stem of 50 g slotted masses   Top

  

5. Images formed by Curved Mirrors

Students use what they have learned about images formed by lenses to investigate those formed by curved mirors. Very little direction is given in this experiment as it parallels the previous one on lenses.

10 cm focal length concave mirror and mirror holder, 10 cm focal length convex mirror, Candle and Screen, Nail or base and stem of 50 g slotted masses   Top

  

6. Ray Tracing

The principle rays are introduced and students draw scaled ray diagrams to predict the nature, position, size and orientation of real and virtual images formed by concave and convex lenses and mirror. Magnification is defined and this is related to the distance of the image and the object from the lens or mirror.

10 cm focal length convex lens and lens holder, 10 cm focal length concave mirror and mirror holder, Candle, screen, nail or base and stem of slotted masses, 10 cm focal length concave lens and lens holder, 10 cm focal length concave mirror and mirror holder, 10 cm focal length convex mirror and mirror holder   Top


7. The Lens Formula

Students measure the distance of the object and its real image from a convex lens for a range of object distances. This leads to the discovery of the formula 1/u +1/v = 1/f. The formula is tested and then tested when a vitual image is formed. The real is positive sign convention is introduced and students learn to calculate the position and size of an image formed by an object near convex and concave lenses and mirrors. Calculations are checked using the apporopriate lens or mirror and using a candle as the object.

10 cm focal length convex lens and lens holder, 10 cm focal length concave mirror and mirror holder, Candle, screen, nail or base and stem of slotted masses.  Top

8. Refraction

Students investigate the saving of a person at the beach and discover the path across the sand and through the water that will result in reaching the person in the smallest possible time. They discover 'Snell's Law' concerning the angles they run and swim when moving along the minimum time path. Using a ray box and a semicircular plasic block they discover the same law applies to light. Refractive index is defined and determined for both plastic and water. Students learn to determine the path light will follow when it passes between any two substances. They check their calculation by putting the plastic block inside the water tank.

Ray/light box and single ray mask, Semicircular plastic block, Semicircular water tank, Protractor   Top


9. Total Internal Reflection and Dispersion

Students discover the conditions needed for TIR to occur and then calculate the critical angle for a plastic/air boundary. They check the prediction with a ray box and a plastic block. They calculate the critical angle for a plastic/water boundary and check their calculation by putting the block into a semicircular water tank. Students then investigate dispersion and determine the refractive index of the plastic block when different colours of the spectrum pass through it.

1 L beaker of water, Small plane mirror/side mirror of the ray/light box is suitable), Ray/light box, Single ray mask, Semicircular plastic block, Semicircular water tank and a Protractor  Top

  

10. The Convex Lens

Students calculate and draw on a large scale diagram, the paths followed by light through a convex lens. The three ligh paths are parallel to the axis of the lens. Students measure angles of incidence and calculate angles of refraction at the air/glass and glass/air boundaries and discover the the position of the principle focus of the lens. They compare their result with the the value obtained using the Lens Makers Formula. A very valuable exercise. Student have been known to say they 'get it better' after completing it.

Ruler, Protractor   Top




11. The Eye part 2



Students investigate how the eye focusses on objects They use a convex lens and a screen to model the eye and replace the lens with one of a different shape when the object is moved. The effect of pupil size and depth of field is studied. Defects of vision are is investigated and students add additional lenses to 'defective' model eyes to produce a sharp image on the scrreen for both long and short sighted eyes.

Convex lenses with focal lengths of 5, 10, 20 and 50 cm, Concave lens with focal length of 50 cm, 2 lens holders, Candle and Screen  Top




12. Fire in Diamonds

Students plot paths of light through a large scale diagram of a diamond with Tolkowski's cut. They discover how to produce the fire effect - the coloured flash. A diamond ring is set up and the students look at it from the predicted direction and find the phenomenon called fire in diamonds.

Ruler, Pacer pencil, Protractor, Ray/light box, Diamond ring, Retort stand, Bosshead and Clamp   Top


13. The Rainbow

Students plot the path of light through the diagram of a large water drop. They predict the angle of exit of the light and the angle subtended at the eye by a rainbow. Students check their calculations using a plastic vial filled with water and a ray box, and viewing the rainbow formed in a water sprinkler.

Ruler, Pacer pencil, Protractor, Plastic vial, Ray/light box, 2 icy pole sticks and a small nut and bolt   Top


14. The Magnifying Glass

In this experiment students construct a 1:2 scale diagram of a person looking at a spider through a convex lens used as a magnifying glass. The concept of angular magnification is introduced and students determine the theoretical value using the scale diagram. Using a spider on a screen, a convex lens and two set squares students check their prediction by measuring the angular magnification as seen when looking through the lens. This is repeated for a range of values, the maximum angular magnification is determined and related to the focal length of the lens.

Ruler, 2 set squares, 10 cm focal length convex lens, holder and screen  Top



Only the left third of the diagram the students construct is displayed.

15. The Compound Microscope

Students use two convex lenses to create a model microscope. They learn how to make the final image form at the distance of the near point. By putting a ruler at the near point they can measure the width of the image when looking into the eyepiece. The theoretical linear magnification is determined and compared with the value calculated from the measurements. The effect that the distance between the lenses has on the magnification is investigated.

Metre ruler and 30 cm ruler, 2 10 cm focal length convex lenses in holders, Candle, Screen, Retort stand, Bosshead and clamp, Set square  Top


16. Telescopes

Students trace rays through a diagram of a Keplerian and a Galilean telescope. The angular magnification produced is related to the focal lengths of the lenses used. The concept of the eyering is introduced. Students construct the two telescopes and view an object at the far end of the room. The angular magnifications produced by the telescopes are determined from a series of measurements and compared with the focal lengths of the lenses. The advantages and disadvantages of the Keplerian versus the Galilean type are discussed.

IEC Laser Optics Show (manufactured by Industrial Equipment and Control (Australia) 61-63 McClure Street Thornbury Victoria 3071 Australia. ph 61 3 9497 2555 fax 61 3 9497 2166 30, 40, or 50 cm focal length convex lens, 10 cm focal length convex lens, 2 lens holders, 2 set squares  Top

  

17. The SLR Camera

Students investigate the following aspects of an SLR camera : method of focussing, the pentaprism and the focussing screen, field of view, size of image, focal ratio of the lens, brightness of image, depth of field, exposure time and ASA of film. They learn how the ASA, focal ratio, and exposure time are interrelated and how the depth of field can be controlled with suitable combinations of the three variables.

SLR camera, 10, 20 and 50 cm focal length convex lenses, 2 Cardboard discs with diameter 5 cm. One disc needs a 1 cm diameter hole in its centre and the other needs a 2 cm diameter hole in its centre. Candle, Lens Holder and Screen  Top


18. Colour Filtration

Students use a computer interface and a light sensor to measure the percentage transmission of the different parts of the complete spectrum through different coloured filters and then plot graphs of percentage transmission versus colour for each filter.

PC and digital/analog interface (10 bit recommended). Light intensity sensor, Triangular glass prism with a high lead content (high refractive index), Stand, Bosshead and clamp, Colour filtration plastic strip printed from the file supplied, Yellow filter from light box kit, Spectroscope, Ray/light box, 12V Power Supply, Red, Green, Blue, Yellow, Magenta and Cyan filters   Top


19. Colour Photography

Students are introduced to the primary colours and their coresponding complimentary colours. Students then go through the process of producing a colour print from a colour negative. They are given a scene and imagine taking a picture of it. They use coloured pencils to fill in the the coloured dyes in the different colour sensitive layers on the film and the printing paper that are produced when they are developed. They colour in the negative and then colour in the print after analysing which parts of the complete spectrum pass through the different combinations of dyes. Senior students really enjoy this exercise. They learn how the colours of a scene are reproduced on a print and they do some colouring - something they haven't done for ages! A Colour transparency file of completed diagrams included.

Ray/light box, 12V power supply, Red, Green, Blue, Yellow, Magenta and Cyan filters, Red, green, blue, yellow, magenta, cyan (Derwent no.41) and black pencils, Spectroscope or IEC Laser Optics Show  Top