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Reflection

18 April 2023

Objectives

Be able to describe what reflection is and draw ray diagrams.

HSW: AF4: Using investigative approaches

Used before in: Will use again in:

PLTS: Independent enquirers: support conclusions, using reasoned arguments and evidence.

Used before in: Will use again in:

KeywordsIncident ray, reflected ray, angle of incidence, angle

of reflection, normal, plane, perpendicular, ray diagram, virtual image.

Starter Question: How big does a mirror have to be so youcan see a reflection of your whole height?

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Outcomes

All students should be able to: Carry out practicals safely to describe

how objects are reflected.Most students should be able to: Be able to draw correct ray diagrams

for reflected objects and state the Law of Reflection.

Some students should be able to: Describe the rules of reflection and

explain what a virtual image is.

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Starter: How big does a mirror have to be so youcan see a reflection of your whole height?

• We will answer this at the end.

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Practical Time

• How is light reflected?

• Your teacher will demonstrate the reflection practical to you.

• SAFETY: Light bulbs will be HOT and make ray boxes hot. Wait for them to cool down before tidying away.

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Law of reflection – check your diagram:

• 1)1) Angle of incidence = Angle of Angle of incidence = Angle of reflection (measured from the normal reflection (measured from the normal line, (the line perpendicular to the mirror line, (the line perpendicular to the mirror plane surface))plane surface))

normalnormal

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Constructing mirror images

• Mirror images from a plane mirror are virtual images.

• This means that if you put a screen behind a mirror reflecting your image you would not get an image of your face on that screen.

• The image isn’t real. • This is the difference, in a

real image you can put a screen in front of the rays of light and produce an image. (there aren’t actually any rays of light behind a mirror – it just looks like there are.)

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Pepper’s Ghost

• Your teacher will demonstrate Pepper’s Ghost.

• How could this have been used by magicians in the past?

• How does it work?

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E

mirror

Practical 2 – constructing mirror images

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Practical 2 – constructing mirror images

• 1 Sketch a letter and what its reflection looks like in the mirror.

• 2 Use the instructions from the board to draw ray diagrams of your initials

mirror

Object

Reflected image

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You have found out the rules of reflection:

• Rules of reflection: The image is always:

• Rule 1: the same …………… behind the mirror as the object is in front.

• Rule 2: The same ……… as the object.

• Rule 3: ………… inverted (left becomes right and right becomes left).

laterally distance size

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Plenary: The big Q: How big does a mirror have to be so you can see a reflection of your whole height?

• 1) Write down the law of reflection

• Draw a diagram of a person standing side on in front of 3 mirrors: 1 the size of their face, 1 the size of half their body, 1 the full length of their body

• 2) How big does the mirror have to be?

• 3) Explain what the image looks like - what are the rules of reflection?

• 4) What is a virtual image?