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Flashcards in Topic 4 Deck (44):

What are two properties of all types of waves?

Reflection and refraction


What’s the normal

Is a line drawn at 90degreez to the mirror surface at the point that the arriving or incident day meets the mirror. The angles i and r are measured from this line


What’s the law of reflection

Angle I=angle r


What is refraction

The change in the direction of a light ray that happens when it travels from one transparent material to another

Notice that the ray of light bends towards the normal as it enters the glass and and away from the normal when it leaves the glass

Rays of light that meet a surface at 90 degrees do not bend at all but simply continue into the material without a change in direction


Why does refraction happen

Because light waves travel at different speeds in different materials


Where does light travel more slowly? In glass or in air?

Travel more slowly in class than they do air


What does total internal reflection involve

Both reflection and refraction


The role of refraction in total internal refraction

Refraction is when light slows down and usually changes direction when it travels from a less dense to a more dense medium

Light slows down and bends towards the normal when moving from air into glass or water


The Role of reflection in total internal reflection

As the angle of incidence increases the angle of refraction will increase until it reaches 90 degrees. At this point the ray of light is travelling along the outer surface of the glass. The angle of incidence is the critical angle.

Above the critical angle the light is totally internally reflected


Describe critical angles

Total internal reflection can only occur when travelling from a dense material like glass meets a boundary with a less dense material like air
Light speeds up and changes direction away from the normal when it travels from glass into air
Total internal reflection can take place with sound as well as light


What are endoscopes

Can be used to look inside patients’ bodies and make use of optical fibres

Endoscopes allow ‘keyhole’ surgery. This is surgery conducted through a very small cut in the body to speed up recovery time


What can happen to couloirs and objects

Transmission reflection and absorption of different wave lengths of light


What is specular reflection

Occurs when waves are reflected from a smooth surface

When parallel rays of light are incident on a smooth plane surface such as a mirro the reflected light rays will also be parallel

The size of any irregularities on the surface are much smaller than the wavelength of the wave


What is diffuse reflection

Occurs when the surface is not smooth and has rough irregularities
The size of the irregularities is comparable with the wavelength of the wave the incident wave is then reflected at many different angles and the reflected rays will not be parallel such as when light is reflected off a painted wall


The colour spectrum

Visible light makes up a very small part of the electromagnetic spectrum

The colours that we see can be split into different colours by a prism

These colours all have a different wavelength, ranging from the longest wavelength at the res end of the spectrum to the shortest wavelength at the violent end


Different absorption at surfaces

The colour of an object appears is based on how the atoms at its surface respond to the light being shone on them. A material appears green because its atoms reflect the green wavelengths and absorb all the others


What are filters

Let through different colours of light and absorb all the other colours for example, a green filter will let through or ‘transmit’ green light and absorb all of the other wavelengths


What are lenses

Pieces of glass that bend light in order to bring it into a focus. Lenses make use of refraction to bend light. The more refraction that occurs the more power the lens has


Lenses use refraction to bend light. There are two types of lens. What are they?




What’s a converging lens

Bends rays of light towards one another bringing them to a point


What’s a diverging lens

Bends rays of light away from each other


What is the power of the lens related to

The shape of it


When parallel light rays from a distant object pass through a converging lens what happens

They are brought to a focus at a point - the focal point of principal focus. The object can be said to be ‘at infinity’ if it’s distance from the lens is much greater than the focal length of the lens


What’s a real image

That can be produced on a screen
The lens focused light rays at the screen


What does the focal length depend on

The thickness of the lens and the material that the lens is made from


When is a real image formed

Where light rays converge and are actually focused on a screen


What’s the nature of s real image

Far from the lens, the real image is upside down and smaller than the object

Moving the object closer to the lens causes the image to become larger. The position of the image will move away from the lens but will remain real and upside down

At a distance of twice the focal length (2F) the object and image are the same size. Between F and 2F the image is magnified


What’s a virtual image

Formed by a converging lens when the object is between the focal point and the lens


What’s a diverging lens produce

Virtual image


What’s a virtual image

Formed by light rays which appear to diverge from that point but do not actually do so


All electromagnetic waves...

Are transverse
Travel at same speed in a vacuum (3 x 10^8 m/s)
Transfer energy to the observer


As the frequency of the radiation increases the wavelength



What’s the electromagnetic spectrum

Radio waves
Visible light
Ultra violet
X rays
Gamma rays


The refraction of a light ray involves a change in :

The direction of the light ray

The speed of the light

Light slows down when it moved from air into glass and speeds up when it moves from glass into air

The only time when the direction does not change is when the beam is travelling along the normal


What are electromagnetic waves composed of

An electric field and a magnetic field at right angles to one another


Electromagnetic waves may be :

Reflected off a surface

Refracted when they move from one material to another

Transmitted when they pass through a material

Absorbed by different materials for example UV is absorbed by the skin but not by the earths atmosphere

The extent to which these four things happen depends on the material and the wavelength of the EM waves


Radio waves and microwaves are both used for

Communicating they have different wavelengths and behave differently in different materials


X-rays and gamma-rays cannot reach the surface of the earth as

They are absorbed by the upper atmosphere


All objects above ________ will emit electromagnetic radiation

Absolute zero.

Their temperature will depend on how much of it they absorb and how much of it they radiate


Emitting radiation

A hot cup of tea at 90 degrees will emit radiation that is mainly in the infrared part of the EM spectrum whereas the suns surface temperature of 5700 degrees means that it emits visible light and ultraviolet radiation which have a shorter wavelength than infrared

Bodies that are much hotter than the sun will emit x-rays


Factors affecting temperature

A body at a constant temperature absorbed the same amount of radiation as it emits

An object will increase its temperature if it absorbs more radiation than it emits

An object will decrease its temperature if it emits more radiation than it aborbs


As the temperature of a body increased ...

More energetic radiation is emitted including infrared visible and UV


Intensity and wavelength

Intensity is the energy emitted per square metre per second or the power emitted per square metre, the intensity and wavelength of the radiation emitted by a body depend on its temperature. As the object gets hotter the intensity increases and the wavelength that correspond to the maximum intensity decreased


Factors affecting the temperature of the earth

Depends on how much radiation is absorbed and how much is emitted