Concave mirrors

Concave MirrorsConcave Mirrors

The laws remain the sameThe laws remain the same

The Sky Mirror in Monte CarloThe Sky Mirror in Monte Carlo

The Sky MirrorThe Sky MirrorWhat do you What do you notice about notice about

the mirror the mirror image you image you

see?see?

Properties of Concave MirrorsProperties of Concave Mirrors

Concave mirrors are shaped curved like a Concave mirrors are shaped curved like a letter C or the inside of a sphereletter C or the inside of a sphere

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

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

How do we draw ray diagrams How do we draw ray diagrams for Concave mirrors?for Concave mirrors?

It all comes back to the…It all comes back to the…• Angle of incidenceAngle of incidence• Incident rayIncident ray• NormalNormal• Reflected rayReflected ray• Angle of reflectionAngle of reflection

SO… How do you do this on a SO… How do you do this on a curved surface?curved surface?

You apply the SAME rules of You apply the SAME rules of reflectionreflection

If you could make the mirror If you could make the mirror INFINITELY small, you would notice INFINITELY small, you would notice that for an instant the mirror acts that for an instant the mirror acts like a flat plane at the point where like a flat plane at the point where light hits itlight hits it

Therefore, you could consider that Therefore, you could consider that the curved mirror is made up of the curved mirror is made up of MANY small flat mirrorsMANY small flat mirrors

Starting with the normalStarting with the normal If a normal (perpendicular line) is drawn If a normal (perpendicular line) is drawn

from each of the ‘flat’ parts of the from each of the ‘flat’ parts of the curved mirror what do you notice?curved mirror what do you notice?

All the lines will meet up at the same All the lines will meet up at the same pointpoint

This is called the CENTER OF CURVATUREThis is called the CENTER OF CURVATURE

The centre horizontal line is the PRINCIPLE AXIS

The Principle AxisThe Principle Axis It is an important feature because it It is an important feature because it

helps you locate the positions of objects helps you locate the positions of objects that are in front of the mirrorthat are in front of the mirror

The spot where the principle axis touches The spot where the principle axis touches the mirror is called the VERTEX or Vthe mirror is called the VERTEX or V

If an incident ray goes through the center If an incident ray goes through the center of curvature it gets reflected back on of curvature it gets reflected back on itself - JUST LIKE IT DOES when light hits itself - JUST LIKE IT DOES when light hits a plane mirror through the normal a plane mirror through the normal (remember the center of curvature is (remember the center of curvature is where the normal all meet)where the normal all meet)

Rays Parallel to the Center of Rays Parallel to the Center of CurvatureCurvature

When rays run parallel to the When rays run parallel to the principal axisprincipal axis what do you notice?what do you notice?

They intersect at the same point on the They intersect at the same point on the principal axisprincipal axis

This know as the This know as the FOCAL POINTFOCAL POINT or or FF And the distance from the mirror And the distance from the mirror (V=vertex)(V=vertex) to to

the focal point is called the the focal point is called the FOCAL LENGTHFOCAL LENGTH

So how do we Draw the So how do we Draw the Diagram?Diagram?

The best way to begin?The best way to begin? Put the bottom of the object on the Put the bottom of the object on the

principle axisprinciple axis Because the principle axis is ALSO a Because the principle axis is ALSO a

normal, this means our IMAGE will normal, this means our IMAGE will also be on the principle axisalso be on the principle axis

The next step is to find the TOP of the The next step is to find the TOP of the image in order to complete the image in order to complete the diagramdiagram

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

the Mirrorthe Mirror

What do you notice about the image?

RIGHT-SIDE UP and BEHIND the mirror

What if the Object is between the What if the Object is between the Focal Point and the Center of Focal Point and the Center of

Curvature?Curvature?

The Process is the The Process is the SameSame

What do you What do you notice about the notice about the image?image?

UPSIDE-DOWN UPSIDE-DOWN and in front of the and in front of the center of center of curvaturecurvature

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

CurvatureCurvature

What do you notice What do you notice about the image?about the image?

It’s UPSIDE DOWN It’s UPSIDE DOWN and SMALLERand SMALLER

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

Lets try a Practice ProblemLets try a Practice ProblemPG 426PG 426

A concave mirror has a focal length A concave mirror has a focal length of 12cm. An object with a height of of 12cm. An object with a height of 2.5cm is placed 40.0cm in front of 2.5cm is placed 40.0cm in front of the mirrorthe mirror

A) calculate the image distanceA) calculate the image distance B) calculate the image heightB) calculate the image height

More PracticeMore Practice

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