Topic 5 - Light and the electromagnetic spectrum Flashcards
Explain reflection with the law of reflection
normal line drawn at 90 degrees to mirror surface at point of arriving or incident ray meets the mirror. The angles I and R (incident, reflected ray) measured from this line
The law of reflection is angle i = angle r
Describe the process of refraction
Refraction- change in direction light ray. happens when travels from one material into another.
ray of light bends towards normal as enters the glass and away when leaves
Rays of light that meet a surface at 90 degrees dont bend but continue into material without changing direction
Explain why refraction occurs
light waves travel at different speeds in different materials.
eg / light waves travel slower in glass than air
Explain the role of refraction in total internal reflection
Refraction is when light slows down and changes direction when it travels from less to more dense medium.
Light slows down and bends towards normal when moving from air into glass or water.
Explain the role of reflection in total internal reflection
As angle of incidence increases, angle of refraction increase until reaching 90 degrees.
Here, ray of light travelling along outer surface of glass.
The angle of incidence = CRITICAL ANGLE.
Above critical angle, light is totally internally reflected
Explain total internal reflection and critical angles
Total internal reflection - light travelling dense material meets a boundary less dense material
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.
In total internal reflection angle i > critical angle c
Explain the difference between specular and diffuse reflection
SPECULAR REFLECTION - occurs when waves are reflected from a smooth surface. When parallel rays of light are incident on a smooth, plane surface eg a mirror, the reflected rays will also be parallel
DIFFUSE REFLECTION - occurs when the surface isnt 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 i reflected off a painted wall
Relate the power of a lens to its focal length and shape
The greater the power of a lens, the more it bends light. This is related to the shape of the lens
Explain the effects of different types of lens in producing real and virtual images
A REAL IMAGE is an image that can be produced on a screen. The lens focuses light rays at the screen. It is formed where light rays converge and are actually focused on a screen.
A VIRTUAL IMAGE is formed by a converging lens when the objet is between the focal point and the lens. A diverging lens provides a virtual image. This is formed by light rays which appear to diverge from that point, but don’t actually do so.
Explain the focal point in relation to a converging lens
parallel light rays from object pass through converging lens, brought to focus at point - the focal point or principal focus.
object ‘at infinity‘ if its distance from lens is greater than focal length of the lens
Explain the nature of a real image
real image is upside down and smaller than object.
Moving object closer to lens causes image to grow. position of image will move away but will remain real and upside down.
At a distance twice focal length (2F) object and image are same size. Between F and 2F, image is magnified
Explain the properties of electromagnetic waves
- they are all TRANSVERSE waves (the em vibrations are at right angles to the direction the wave is travelling)
- travel at the same speed (3 x 10^8 m/s) in a vacuum
- transfer energy to the observer
Explain the properties of electromagnetic waves
- they are all TRANSVERSE waves (the em vibrations are at right angles to the direction the wave is travelling)
- travel at the same speed (3 x 10^8 m/s) in a vacuum
- transfer energy to the observer
- they are composed of an electric field and a magnetic field at right angles to one another
Explain precautions needed to be taken when investigating refraction in rectangular glass blocks in terms of the interaction of electromagnetic waves with matter
- when carrying out the investigation, make sure that you direct a thin beam of light towards the point at which the normal makes contact with the glass block. Clearly mark the angles from 0 - 80 with a sharp pencil and ruler
- remember the angle of incidence is measured with respect to the normal line
- light will slow down more when it travels from air into glass than it will when it travels from air into water. This is because the ‘optical density’ of glass is greater than that of air
List the electromagnetic waves in order of longest wavelength and lowest frequency first
Radio Microwave Infrared Visible Ultraviolet X rays Gamma
(Red monkeys in vans use x ray glasses)
Describe the electromagnetic spectrum
the electromagnetic spectrum is continuous from radio waves to gamma rays and that the radiations within it can be grouped in order of decreasing wavelength and increasing frequency.
AS THE FREQUENCY OF THE RADIATION INCREASES, THE WAVELENGTH DECREASES
Which em frequencies can our eyes pick up on
Our eyes detect the part of the electromagnetic spectrum that is visible light, but there are other wavelengths that behave differently.
Explain the behaviour of em waves
Electromagnetic waves may be:
- reflected off a surface
- refracted when the 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 earths atmosphere
The extent to which these four things happen depends on the material and the wavelength of the EM waves
Explain the effects of differences in the velocities of electromagnetic waves in different substances
Electromagnetic waves have different velocities in different materials. This is linked to an extent to the density of the material.
The speed of light in a diamond is around 40% of the speed of light in a vacuum or air, due to the high optical density of diamond
Explain how all bodies emit radiation
All objects above absolute zero will emit electromagnetic radiation. Their temperature will depend on how much of it they absorb and how of it they radiate .
Explain how all bodies emit radiation
All objects above absolute zero will emit electromagnetic radiation. Their temperature will depend on how much of it they absorb and how of it they radiate .
Bodies that are hotter than the sun will emit x rays
Explain the factors affecting temperature of the body when emitting radiation
- A body at a constant temperature absorbs 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 absorbs
As the temperature of the bod increases, more energetic radiation is emitted including infrared, visible and UV
Explain the factors affecting temperature of the earth
The temperature of the earth depends on how much radiation is absorbed and how much is emitted
Explain how to investigate the nature of a surface affects the amount of thermal energy radiated or absorbed
METHOD 1:
- Fill leslies cube (shows how the nature of a surface affects the rate at which thermal energy is absorbed or emitted) with hot water a known temperature. Place a thermometer a small distance away from each of the sides. Plug the top of the cube with a bung
- Measure the temperature at a distance of 10cm from each of the four sides of leslies cube for a period of 5 minutes, taking a reading every 30 seconds.
METHOD 2:
- Fill leslies cube with the same volume of cold water at a known temperature. Plug the top of the cube with a thermometer and bung
- Heat each side, one at a time, with a radiant heater from the same distance away (about 10 cm)
- Record how the temperature of the water changes, every 30 seconds, over an appropriate period of time k
Explain precautions that can be taken when investigating the nature of a surface affects the amount of thermal energy radiated or absorbed
- be careful when using hot water as it may scald
- conduct the investigation accurately and fairly by ensuring that the thermometer used Is the same for each surface, the distance from the surface is the same and the starting temperature is the same in each case. Take the same number of readings over the same time period and intervals
Explain how the danger of an electromagnetic wave can increase
the potential danger associated with an electromagnetic wave increases with increasing frequency
Explain changes in atoms and nuclei
Changes in atoms and nuclei can:
- generate radiations over a wide frequency range
- be caused by absorption of a range of radiations
Explain the effect of radio waves on electrical circuits
radio waves can be produced by, or can themselves induce, oscillations in electrical circuits
