© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 27 KS4 Physics Reflection

© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20051 of 27

KS4 Physics

Reflection


Reflection

Ray diagrams

Reflection

Curved mirrors

Summary activities

Plane mirrors

Contents


Beams of light travel in straight lines. We can see this when we look beams of light such as search lights, laser beams, car head lights and torches.

This is why we can not see around corners and why shadows are formed.

Beams of light


We can investigate light by using ray boxes in a darkened room. Ray boxes produced a narrow beam of light (called a light ray) which makes it easier to study effects such as reflection and refraction.

Ray boxes


When we draw a diagram of an experiment using a ray box we represent the beam of light using a straight line. An arrow is placed on the beam showing the direction the light is travelling in.

When we draw a ray diagram we must:

Use a sharp pencil

Draw clearly and accurately

Ray diagrams


When we draw a ray diagram and a ray of light hits the surface of an object we add a line to the diagram called the normal. The normal is drawn at right angles (90°) to the surface the ray has hit.

The normal is drawn in as we can measure the angle between the ray and the normal.

The normal

normal


Reflection

Ray diagrams

Reflection

Curved mirrors

Summary activities

Plane mirrors

Contents


A luminous object gives out light and can also be called a light source.

Light travels in a straight line directly into your eye.

How does light from a light bulb and other light sources reach your eye?

Seeing luminous objects


Objects that do not give out light are non-luminous.

Light from the light source strikes the book and some of the light is reflected into your eye.

How does your eye see non-luminous objects such as a book?

Seeing non-luminous objects


Transparent materials, such as glass, let nearly all the light that falls on them pass through. Very little light is reflected or absorbed by the material.

Opaque materials, such as wood, do not let any of the light that falls on them pass through. All the light is either reflected or absorbed by the wood.

Translucent materials, such as frosted glass, let some of the light that falls on them pass through. The rest of the light is reflected or absorbed by the material.

Transparent, opaque and translucent


Shiny surfaces reflect a lot more of the light that falls on them than matt surfaces.

Mirrors are pieces of glass with a coating of silver on one side. The silver reflects the light passing through the glass. If the surface of the silver is flat we are able to see reflected images clearly, because the light from them is reflected by the mirror into our eyes.

Shiny surfaces

They often look brighter than surrounding objects as more of the light falling on them is reflected into our eye. You can often also see reflections of other objects on their surface.


Some mirrors are curved. These give distorted images.

If a mirror curves inwards then it is a concave mirror; if it curves outwards it is a convex mirror.

When we draw a ray diagram we represent a mirror by drawing a line with dashes on the silvered (non-shiny) side. Most mirrors are flat and these are called plane mirrors. They give non-distorted lifelike images.

A plane mirror

A concave mirror

A convex mirror

Types of mirror


Reflection

Ray diagrams

Reflection

Curved mirrors

Summary activities

Plane mirrors

Contents


Reflected ray

Incident ray

i r

angle of incidence (i) = angle of reflection (r)

This is called the law of reflection and is true for any type of wave being reflected from a surface.

Law of reflection


By positioning two plane mirrors at 45° to each other at either end of a tube we can make a periscope.

Periscopes are used in submarines to see what is on the surface of the water from underwater.

The periscope


When you look at some writing in a mirror you will notice that it appears backwards. We can work out what is happening by drawing a ray diagram.

The light rays swap over when they are reflected. This causes the image to appear laterally inverted (backwards) when compared to the original object.

cat

Lateral inversion


When you look at a mirror you see a virtual image that appears to be behind the mirror.

distance distance

The image appears to be the same size as the original object and the same distance behind the mirror as the object is from the mirror.

virtual image

Virtual images

object


Reflection

Ray diagrams

Reflection

Curved mirrors

Summary activities

Plane mirrors

Contents


The distance between the mirror and the focal point is called the focal length (ƒ). The more curved the mirror is the closer the focus is to the lens.

Concave mirrors reflect rays of light to a focal point (F).

Concave mirrors are converging mirrors, as the rays of light converge to a focus. If a light source is placed at the focus they produce a beam of parallel light rays.

Concave mirrors

F

f


ƒChose a distant object (to get parallel rays of light).

Finding of a concave mirror.

Hold a plain white screen in one hand.

Focal length of concave mirrors

Hold the mirror in the other hand and move it closer to the screen until a clear image appears.

Use a ruler to measure the distance between the lens and the screen - this is the focal length (ƒ).


Concave reflectors are used to focus signals from distant satellites.

Concave mirrors are used in allowing them to be more powerful for their size.

Uses of concave mirrors


Convex mirrors reflect rays of light away from a focal point.

Convex mirrors are diverging mirrors. The parallel are reflected so they appear to have come from a spot called the focus.

Convex mirrors

F

f


Convex mirrors are often used to see around corners, here in a busy corridor.

The rear view mirror in a car is a convex mirror to widen the field of view.

Uses of convex mirrors


Reflection

Ray diagrams

Reflection

Curved mirrors

Summary activities

Plane mirrors

Contents


Glossary

concave mirror – A mirror that curves in at the centre.convex mirror – A mirror that curves out at the centre.incident ray – The light ray that strikes a surface.law of reflection – When light is reflected, the angle of

incidence equals the angle of reflection.lateral inversion – The reversal of an image in a mirror,

which means that the left-hand side appears on the right and the right-hand side appears on the left.

normal – A line on a ray diagram drawn at right angles to the surface being hit by the light ray.

plane mirror – A mirror with a flat surface.reflected ray – The light ray bounced back from a surface.ray diagram – A diagram that shows what happens to

light rays during processes such as reflection.


Anagrams


Multiple-choice quiz

Documents

© Boardworks Ltd 2004 1 of 20 © Boardworks Ltd 2005 1 of 27 KS4 Physics Reflection