Topic 4 Flashcards
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?
Converging
Diverging
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
Decreased
What’s the electromagnetic spectrum
Radio waves Microwaves Infrared Radiation 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
