Chapter 11.pdf

We use fibre optics systems to transmittelephone and Internet communications. A singleoptical fibre can be as thin as a human hair, yettransmit thousands of different signals at the sametime (Figure 11.28). This is because each signal issent at a different wavelength through the samecable. Just as two flashlight beams can cross eachother and then continue on their way unaffected,thousands of light beams can pass through the samecable. A typical optical fibre cable can be made fromthousands of optical fibres tightly packed together.Figure 11.28 A single optical fibre can fit through the eyeof a needle.D17 Quick LabObserving RefractionPurposeTo observe whether the bending of light affects theway we see certain objectsMaterials & Equipment• glass of water• pencil• jar lid with opaque rim• coinProcedure1. Insert a pencil into the glass of water. Observe theglass from the side at various angles. Record yourobservations using labelled diagrams.2. Place a jar lid with an opaque rim on a desk andput a coin in the middle.3. Keep watching the coin while you lower theheight of your head until the coin just disappearsfrom view behind the rim of the lid (Figure11.29).4. Keeping your head at the same level, pour waterinto the lid, on top of the coin. Observe. Recordyour observations using labelled diagrams.Figure 11.29 Step 3Questions5. Describe the path of light from the water to theair.6. Draw a ray diagram of the light rays from the cointo your eye:(a) in step 3(b) in step 47. Compare your drawings in question 6 with thosedone by classmates.(a) How are your drawings similar?(b) How are your drawings different?Ray diagrams model the behaviour of light in mirrors and lenses.435