Concave mirrors

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  • Concave MirrorsThe laws remain the same

  • The Sky Mirror in Monte Carlo

  • The Sky MirrorWhat do you notice about the mirror image you see?

  • Properties of Concave MirrorsConcave mirrors are shaped curved like a letter C or the inside of a sphere

    You can identify them from other mirrors because light goes into them like entering a CAVE

    Examples: the side of spoon you put food on, a makeup mirror, a satellite dish

  • How do we draw ray diagrams for Concave mirrors?It all comes back to theAngle of incidenceIncident rayNormalReflected rayAngle of reflectionSO How do you do this on a curved surface?

  • You apply the SAME rules of reflectionIf you could make the mirror INFINITELY small, you would notice that for an instant the mirror acts like a flat plane at the point where light hits itTherefore, you could consider that the curved mirror is made up of MANY small flat mirrors

  • Starting with the normalIf a normal (perpendicular line) is drawn from each of the flat parts of the curved mirror what do you notice?

    All the lines will meet up at the same pointThis is called the CENTER OF CURVATUREThe centre horizontal line is the PRINCIPLE AXIS

  • The Principle AxisIt is an important feature because it helps you locate the positions of objects that are in front of the mirrorThe spot where the principle axis touches the mirror is called the VERTEX or VIf an incident ray goes through the center of curvature it gets reflected back on itself - JUST LIKE IT DOES when light hits a plane mirror through the normal (remember the center of curvature is where the normal all meet)

  • Rays Parallel to the Center of CurvatureWhen rays run parallel to the principal axis what do you notice?

    They intersect at the same point on the principal axis

    This know as the FOCAL POINT or FAnd the distance from the mirror (V=vertex) to the focal point is called the FOCAL LENGTH

  • So how do we Draw the Diagram?The best way to begin?Put the bottom of the object on the principle axisBecause the principle axis is ALSO a normal, this means our IMAGE will also be on the principle axisThe next step is to find the TOP of the image in order to complete the diagram

  • How to draw Objects between the Focal Point and the Mirror

  • What do you notice about the image?RIGHT-SIDE UP and BEHIND the mirror

  • What if the Object is between the Focal Point and the Center of Curvature?

  • The Process is the Same

  • What do you notice about the image?UPSIDE-DOWN and in front of the center of curvature

  • What about when the object is in front of (or beyond) the Center of Curvature

  • What do you notice about the image?


  • You can also Predict what your image looks like using equations!

  • Lets try a Practice ProblemPG 426A concave mirror has a focal length of 12cm. An object with a height of 2.5cm is placed 40.0cm in front of the mirrorA) calculate the image distanceB) calculate the image height

  • More PracticeRead pages 419-430TB: questions 427, 1-5WB: pg 134-136STSE: TB 428-429 due Monday

    Pg 420Pg 420Pg 420


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