Reflection of light

1You can have a view of yourself if you look into a mirror. calm water surface. a piece of shiny metal wall. a piece of window glass.

2Now you look into a mirror and see the image of yourself. In front of the mirror. On the surface of the mirror. Behind the mirror.

3Alex says, ‘Your mirror image is smaller than yourself’. Do you agree? Yes, the image is really smaller. No, your image and you are always of the same size. It looks smaller just because it is far from you. No, it depends on how far you stand from the mirror. Others: ________.

n A ray of light bounces off a plane mirror. mirror This is an example of reflection of light. 1Laws of reflection

n useful words to describe the reflection of light reflected ray incident ray normal mirror angle of incidence angle of reflection 1Laws of reflection

Laws of reflection Simulation

The incident ray,the reflected ray and the normalall lie in the same plane. normal incident ray reflected ray mirror normal incident ray reflected ray mirror Laws of reflection

normal incident ray reflected ray mirror angle of incidence angle of reflection = Laws of reflection

Regular reflection parallel incident rays parallel reflected rays on a flat, smooth surface e.g. mirror 2Regular and diffuse reflection

Diffuse reflection on a rough, not perfectly smooth surface e.g. cover of a book parallel incident rays reflected rays in different directions 2Regular and diffuse reflection

Q1The angle between the… The angle between the incident ray and the _______ is called the angle of incidence. normal The laws of reflection state that it is equal to the angle of ___________. reflection

Q2The angle between an… The angle between an incident ray and the mirror is 20 . The angles of incidence and reflection are ____  and ____ . The mirror turns the ray by ____   70 

Q3True or false: Reflection of… True of false: Reflection of light by a rough surface does not obey the laws of reflection. (T/F)

Images formed by a plane mirror Simulation

n Rays from object O become divergent after reflection. 3How a plane mirror forms an image mirror O

I is a virtual image. – cannot be picked up on a screen Reflected rays appear to come from I behind the mirror. mirror O 3How a plane mirror forms an image I

by geometric construction OI virtual rays shown by dotted lines Locating the position of the image 3How a plane mirror forms an image

OI ⊥ MN N M ON = NI OI The ray diagram shows that Locating the position of the image 3How a plane mirror forms an image

Locating the position of the image 3How a plane mirror forms an image Simulation

3 virtual 1 behind the mirror 2 of same size as the object 4 laterally inverted 3How a plane mirror forms an image Properties of the image formed by a plane mirror mirror object image

3How a plane mirror forms an image Properties of the image formed by a plane mirror Simulation

Example 1 A device consists of 2 mirrors at right angles to each other. Complete the path of the ray. M1M1 45  M2M2 The ray is turned back. parallel but opposite in direction

Example 2 A girl can just see her feet at the bottom edge of the mirror. Her eyes are 10 cm below the top of her head. 150 m (a)What is the distance between the girl and her image in the mirror?

Example 2 (a)Image distance =  Distance = 150  2 = 300 cm Object distance

Example 2 (b)How high above the floor is the bottom edge of the mirror? h 11 22

h 11 22 Example 2 (b)How high above the floor is the bottom edge of the mirror? By laws of reflection,  1 =  2 = 70 cm The bottom edge of the mirror is 70 cm above the floor.  h = 

Example 2 (c)What is the minimum height of the top edge of the mirror if she is able to see the top of her head?

Example 2 33 44 h 11 22 10 cm a b By laws of reflection,  3 =  4 = 5 cm Minimum height of top edge of the mirror  b = a =  = b =145 cm above the floor 140 cm

Q1Which of the following… Which of the following descriptions about the image formed by a plane mirror is INCORRECT ? ALight rays come from the image to our eyes. BThe image cannot be projected on a screen. CIt is as far away from mirror as the object is in front. DIt is virtual.

Q2Leon and Partick look in a... Leon and Patrick look in a plane mirror placed directly in front of Leon. Can they see themselves and each other in the mirror? Leon can see himself but Patrick cannot. Both of them can see each other

Q3True or false: If the boy... True or false: If the boy walks closer to the plane mirror, the image position of the candle will change. (T/F)

Q4A boy of height 1.5 m stands... A boy of height 1.5 m stands 5 m in front of a plane mirror. His image is ______ m tall and ______ m from him

Q5The ray diagram shows the... The ray diagram shows the extension of one of the reflected rays. Locate the image by completing the ray diagram.

Q6Jenny views herself in a... Jenny views herself in a full-length mirror. (a)Construct lines from the images of Jenny’s feet and top of her head to her eyes.

Q6Jenny views herself in a... Jenny views herself in a full-length mirror. (b)Mark on the mirror to indicate minimum region Jenny uses to see her full image.

Q6Jenny views herself in a... (c)Does this region of the mirror depend on Jenny’s distance from the mirror? (Yes/No) Jenny views herself in a full-length mirror.

Fun with Two Mirrors n Simulation Simulation n Game Game