Chapter 11.pdf

Solar OvensA solar oven, also called a solar cooker, is adevice that uses light from the Sun as its energysource. A solar oven transforms sunlight directlyinto heat that can be used for cooking or boilingwater (Figures 11.14 and 11.15). By making use ofsolar energy, precious resources can be saved. Forexample, trees are scarce in the Himalayas andusing solar energy instead of wood for heat helpspreserve forests.A solar oven uses several strategies forproducing heat, such as using a concave mirror toconcentrate the Sun’s rays, converting light toheat through absorption if the interior of the ovenis a dark colour, and using a clear cover so thatthe Sun’s rays can enter but very little heat canleave. The most efficient ovens create aninsulated space where the food is cooked.Figure 11.14 A man examines a solar oven that is heating water inLadakh, high in the Himalayan Mountains.Calculating MagnificationConcave mirrors have a number of usesincluding magnification. Magnification is themeasure of how much larger or smaller an imageis compared with the object itself. Themagnification of an image, as compared with theobject, may be the same size, enlarged, ordiminished (smaller). Magnification is expressedas a ratio of the height of the image to the heightof the object.Figure 11.15 This solar oven is located on a city rooftop.magnification =image heightobject heightorhM = ih oMagnification can also be determined by taking the ratio of thedistance from the image to the mirror and the distance from the objectto the mirror.Suggested Activity •D15 Inquiry Activity on page 430image distancedmagnification = or M = iobject distanced oThese are very general definitions of magnification. You can useeither formula to determine magnification. Be sure to use the sameunits for both heights or both distances in the calculation. However, nounits are required in the answer since the units cancel out during thecalculation. If the image is bigger than the object, then themagnification will be greater than 1. If the image is smaller than theobject, the magnification will be less than 1.Ray diagrams model the behaviour of light in mirrors and lenses.423