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Name : ........................................... PHYSICS - UNIT 1 "SIGHT AND LIGHT" What is “The Introductory Activity?” The Introductory Activity is a set of short practical tasks designed to stimulate your interest in the topic and to encourage you to come up with questions, called Context Questions, for which you would like answers. These "Context Questions", will form an important part of the work of this topic. Typical Context Questions might be:How does a microscope work?, How do telescopes differ?, Why does light bend?, How is a rainbow formed? After the short practical tasks, you are asked to come up with about three questions of your own that you would like answers to. You will then form a group of three with two others to compare your questions and come up with a list of about six questions that the group thinks are worthwhile. When you have done this, your group will combine with another group and produce a list of about nine questions. After this, the questions from these large groups will be combined for the whole class. What's the purpose of the Context Questions? The questions will guide our work during the topic. Answers to many of the questions will come up during class work, experiments, problem solving and general reading. At the end of the topic you will need to submit answers to a selection of the questions. 1. - Reflection of Light. How do flat or “plane” mirrors work? Place a strip mirror upright in the middle of the page parallel to the short edge. Now draw a line along the back of the mirror. - Place two pins in the page, so that they are in a line pointing towards the mirror at an angle between 30 and 60 degrees, and placed a few cms apart. - With your eye down at mirror level, look into the mirror and move your head to locate the images of the two pins in the mirror. - Move your head until the images of the pins in the mirror appear one behind the other. - Now place two extra pins in the page between your eye and the mirror so that these two pins line up with the images of the first two pins. - Now move the pins and mirror away and draw lines through each of the pairs of pins towards the mirror line. Where do your two lines cross? ........................................................................................................................ - Draw a line at right angles to mirror line where the two lines cross and measure the two angles between this line and your two pin lines. How do the angles compare? ......................................................................................................................... 2. Large Curved Mirrors (Diam = 60cm) There are two large mirrors. One curves inwards and is called “Concave”, the other curves outwards and is called “Convex”. - For each mirror, walk up to it from several metres away. Describe how your appearance or “image” changes. (Refer to size, direction and distortion if any.) Concave Mirror ......................................................................................................................... ......................................................................................................................... Convex Mirror ......................................................................................................................... ......................................................................................................................... Where have you seen Convex mirrors like this before? ......................................................................................................................... Stand about a metre in front of the convex mirror and then in front of a plane mirror and compare how much of the room you can see in each of them. In which type of mirror can you see more? ......................................................................................................................... 3. Making Light bend - Place the glass block with the largest side down in the middle of the sheet of paper and draw a line along each of the four edges. - Now place two pins in a line, a few cms apart, to meet a long edge at about 45 degrees. - Looking through the glass block from the other side, place two more pins in the paper, about a few cms apart, so that all four pins appear to line up. - Now draw lines through each pair of pins to meet the nearest edge. - Connect up these two lines in the space where the glass block was by a straight line. The line represents the path taken by the light as it travels from the head of the first pin through the glass block to the head of the last pin, and then to your eye. Describe what happens to the light as it travels from air into the glass block and what happens as it leaves the glass block into the air. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... 4. How deep is the pool? When you look into a swimming pool, the water does not appear as deep as it really is. This experiment explores this phenomenon. - Place the smallest face of the glass block on the sheet of graph paper. Now look down through the glass block at the graph paper. What do you notice? ......................................................................................................................... - Now slide the small sheet of graph paper up the side of the block until the pattern inside the block and the pattern outside the block match up. The raised sheet of paper indicates that the glass made the bottom sheet appear closer to you. This is because light is slowed down in glass. - You can calculate how much the light has slowed down by measuring the distance from the top of the block down to where you raised the graph paper and dividing this by the height of the block. - Make your measurements and calculate how much you think the light is slowed down by the glass. ......................................................................................................................... ......................................................................................................................... 5. How can a magnifying glass be flat? The clear plastic sheet has two sections. A rectangle at the bottom and twenty small squares at the top. - Place the rectangle over the printed page and slowly lift the plastic sheet. What do you notice? ......................................................................................................................... What happens as you look through the small squares? - Now lift the convex lens (fatter in the middle) off the page, then the concave lens (thinner in the middle). Which type of lens is the rectangle like? ......................................................................................................................... Look closely at the surface of the rectangle what do you notice? ......................................................................................................................... On the bench is a flat lens taken from an Overhead Projector. Compare it with the plastic sheet. These types of lenses are called Fresnel Lenses. Flat lenses like these are often found on the rear windows of vans. Why? .......................................................................................................................... .......................................................................................................................... 6. Investigating a Slide Projector - Use the information on the slide in the slide projector to measure and calculate how much the projector magnifies the slide. ......................................................................................................................... ......................................................................................................................... How would you move the projector to get greater magnification? ......................................................................................................................... To get back into focus do you have to now move the lens closer or further away from the slide? ......................................................................................................................... 7. Binoculars and Telescopes Look through the each and describe how the images compare. .......................................................................................................................... .......................................................................................................................... Binoculars are telescopes, but they have to produce images which are the right side up, but the lenses are exactly the same as the telescopes. Suggest how they do it. (Hint: Consider the path the light must take in the binoculars to reach your eye and how it might do this) .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... 8. Rainbow produced by a prism. Draw the path of two different colours from the light source, through the prism and onto the screen, which colour is bent the most? .......................................................................................................................... 9. Colour Mixing using Light boxes, colour slides and a screen. Use three light boxes, one for each colour slide. Find the effect of mixing the following colours: Red + Blue, Red + Green, Blue + Green, and Red, Blue + Green. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... 10. Using Colour to make 2-D appear as 3-D Place the red and blue filters over each eye and look at the picture in the text book. 11. Laser Communication The laser beam is carrying the radio signal which can be picked up and decoded by the receiver. DO NOT LOOK DOWN THE LASER BEAM. - Place your hand in the way of the beam and see what happens. .......................................................................................................................... - Shine the laser beam in one end of the optical fibre and point the other end at the receiver. Does the signal go through? .......................................................................................................................... If light travels in straight lines , how do you think it goes through the glass fibre? .......................................................................................................................... 12. Schmidt-Cassegrain Telescope The telescope is an expensive, precision instrument. Care must be taken with it. Do not touch the glass front at all. Only adjust the focus knob, nothing else. Look through the eyepiece and note the magnification. Look through the opening into the mechanism and describe the path you think the light takes through the telescope to you eye. .......................................................................................................................... .......................................................................................................................... Context Questions:From doing the tasks and your other interests, write down 2 or 3 questions for which you would like answers. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... Some Context Questions - Why does a magnifying glass enlarge objects? - How does a telescope work? - What would be the effect of swapping the lenses in a telescope? - How does a Fresnel lens differ from a normal lens? - How does an optometrist make lenses 8. Investigating Telescopes There are many different types of telescopes using different types of lenses. a) An early type was called the Keplerian telescope which consisted of two convex lenses. Look through the telescope at a distant object and describe the image. ......................................................................................................................... ......................................................................................................................... b) Galileo used a telescope using a concave lens as the eyepiece lens. Look through this telescope and compare the image with that of the Keplerian telescope .......................................................................................................................... .......................................................................................................................... 6. Investigating the Microscope The lenses have been selected and arranged to make a microscope. - Look through the eyepiece lens at the far screen and describe what you see. ......................................................................................................................... - Move the eyepiece lens towards the other lens called the “objective” lens and describe what you see. .........................................................................................................................
