05. light physics form 4

8/12/2019 05. LIGHT Physics form 4

1/11

Reflection

Reflection of Light

Note: Both the angle of incident and angle of

reflection must be measured from the normal.

Laws of Reflection

1. The angle of incidence is equal to the

angle of reflection; the ray leaves the

surface at the same angle as it arrives.

2. The incident ray, the reflected ray and

the normal all lie in the same plane; all

three could be drawn on the same flat piece

of paper

Type of Mirror Plane Mirror

Images in plane mirrors

1.

Figure to the left shows how, by reflecting

light, a plane mirror forms an image of a

point source of light such as a small light

bulb.

2.

The image forms in a mirror is

a.

Upright

b. Virtual


2/11

Reflection

Curved mirrors

1.

A curve is part of a circle. Therefore

a. the centre of the circle will also be the

centre of the curve and is called the

centre of curvature, and

b. the radius of the circle will be equal to the

radius of the curve, called the curvature

radius.

Important Terms


3/11

Reflection

We Make Learning Easy

Rules in drawing ray diagram

Concave Mirror

The ray of light through C. This is reflected

back through C.

The ray of light parallel to the principal axis.

This is reflected through F.

The ray of light through F. This is reflected

parallel to the principal axis.

Convex Mirror

A ray towards C is reflected back along its own

path.

A ray parallel to the principal axis is reflected as

if it came from F.

A ray towards F is reflected parallel to the

principal axis.


4/11

Reflection

The Ray Diagram and the Types of Image

Convex Mirror

The image formed by a convex mirror is always virtual, upright and smaller than the object.

Concave Mirror

The characteristic of the image formed by the concave mirror depends on the position of the object.


5/11

Refraction

1. Refractionis the bending of a light ray at the boundary of

two medium as the light ray propagates from a medium to

another with difference optical density.

2. Light passes into an optically denser medium will bend

towards the normal; light passes into an optically less

dense medium will bend away from the normal.

Laws of Refraction1.

The incident and refracted rays are on opposite sides of

the normal at the point of incidence, and all three lie in the

same plane.

2. The value ofsin

sin

i

ris constant for light passing from one

given medium into another. This is known as Snell's law.

Refractive Index (n)

speed of light in vacuumrefractive index =

speed of light in medium
http://www.onlinetuition.com.my/


6/11

Total Internal Reflection

Total Internal Reflection and Critical Angle

1. Total internal reflectionis the reflection of light at the

boundary of 2 medium where the angle of incident

exceeds the critical angle of the medium.

2. The critical angleis the angle of incident in an optically

denser medium for which the angle of refraction is 90.

Total Internal Reflection and

Refractive Index

Requirements for Total Internal Reflection to occur.

1. The light ray must propagate from an optically denser

di t ti ll l d di

Phenomena Related to Total Internal

R fl ti


7/11

LensesTypes of Lenses

Convex lens/

Converging lens/

Positive lens

Concave lens/

Diverging lens/

Negative lens

Principle Focus and Focal Length

1.

The principle focus(F)of a lens is the point on

the priciple axis to which all rays originally

parallel and close to the axis converge, or from

which they diverge, after passing through the lens.

2. The focal lengthof a lens is the distance between

the optical centre an the principle focus.

Power of a Lens

The powerof a lens is defined as the

reciprocalof the focal length in unit meter.

1P

f

The Lens Equation

fvu

111

Conventional symbol

itif tif


8/11

Light 4The Ray Diagram

Convex Lens

A light ray passes through the optical centre of

the lens will not be refracted.

A light ray parallel to the principle axis of the

lens will be refracted passes through the

principle focus.

A light ray passes through principle focus will

be refracted parallel to the principle axis.

Concave Lens

A light ray passes through the optical centre of

the lens will not be refracted.

A light ray parallel to the principle axis will be

refracted away from the principle focus

A light ray moving towards the optical centre

will be refracted parallel to the principle axis.

1.

As with a curved mirror, the position and size of an image can be found by drawing a ray diagram.

2. Any two of the following three rays are sufficient to fix the position and size of the image:3. The ray diagrams of concave lens and convex lens, and the natures of its image is shown in the table next page.


9/11

Light 5

We Make Learning EasyMore notes at http://www.onlinetuition.com.my

The projector

Bulb1. Bulb with high brightness is used.

2.

The bulb must be placed at thecentre of curvature of the concave

mirror.

Concave mirror1. The function of the concave mirror

is to reflect and focus light that

shines on it to the direction of the

condenser.

2. This is to increase the brightness

of the image.

Slide1. The slide acts as the object.

2. It is located at a distance between

f and 2f from the projector lens so

that the image produced is real

and magnified.

3. It is purposely placed upside down

so that the image forms on the

screen looks upright.

Condenser1. The condenser consists of two

Plano-convex lenses.2. The function of the condenser is

to focus all the light that brightens

the whole slide.

3. It also acts as a heat insulator to

stop heat from the bulb so it does

not spoil the slide.

Projector Lens1. The projector lens projects the

image on the screen that is placeda few meters away.

2. It can be adjusted to focus a sharp

image.

ImageThe image produced is

real (it form on a screen)

magnified

inverted (Since the slide is

placed upside down, hence the

image looks upright)


10/11

Light 5


Compound Microscope

Object:

1. The object must be placed in

between the F and 2F of theobjective lens.

2. This is to produce a real and

magnified image.

Magnification power

= Power of objective lens x Power of

eyepiece

m = mox me

Image of objective lens1.

Real

2.

Inverted

3.

Magnified4. Place between the principle

focus and optical centre of the

eyepiece

Eyepiece1.

The power of the eyepiece is

lower than the power of

objective lens.

Distance between the 2 lenses

Distance between the 2 lenses > fo+ fe

Image of the eyepiece

1.

Virtual2.

Inverted

3.

Magnified


11/11

Light 5


Astronomical Telescope

Magnification Focal length of

objective lens

Focal length of

eyepiece

Distance between the 2 lenses

= Focal length of the objective lens

+ Focal length of the eyepiece

= fo+ fe

Image of the Objective Lens

Image of objective lens es1. Real

2. Inverted

3. Smaller

The image of the objective lens acts as

the object of the eyepiece

o

e

fmf

Eyepiece1.

The power of the eyepiece is

higher than the power ofobjective lens.

2. This is to produce a greater

magnification to the image.

Image of the EyepieceThe image produced is

1. real (it form on a screen)

2. magnified

3.

inverted (Since the slideis placed upside down,

hence the image looks

upright)

Object:

The object is at infinity.

Therefore, the light rays isalmost parallel when

reaching the eye lens, and

hence form an image at the

principle focus (Fo)

05. light physics form 4

Documents