Unit 1 Light G10 Flashcards
Outline how we see non-luminous objects
We see non-luminous objects when light bounces off of them.
Describe how we see non-luminous objects.
Non-luminous objects are only seen because of daylight, or when other light bounces off them reflecting into our eyes.
Outline the difference between luminous and non-luminous objects.
Luminous emits light while non-luminous reflects light.
Give examples of luminous and non-luminous objects in the table below
Luminous:
TV screens
Bulb
The Sun
Lasers
Non-luminous:
Smoke
Dust
Mist
Describe the difference between luminous and non-luminous objects.
Luminous emits light, while non-luminous you see in daylight or because light reflects off of objects, which enters your eyes.
Producing light without heat is called:
luminescence
Explain the difference between luminous and non-luminous objects.
Luminous emits light, while non-luminous you see in daylight or because light reflects off of objects, which enters your eyes. All objects you can see that do not produce their own light are reflecting light from another source. This is known as illumination. Some objects produce light without becoming very hot. They generate light through chemical reactions or other processes
Fluorescence
Fluorescence is where a substance absorbs shorter-wavelength ultraviolet light and then gives off light in the visible range of wavelengths.
Electroluminescence
Electroluminescence, which is a substance that gives off light when an electric current passes through it.
Transmission, diffuse reflection, regular reflection and absorption
Look at graph in doc
Bioluminescence
Bioluminescence is the production of light by living things as a result of chemical reactions.
Outline why some things look white and others black
Some things look white because they represent objects that reflect light off of them, since all wavelengths and colors of the spectrum are reflected, the object seems white to the observer. Some objects are black, and absorb the light rays with no relfection. Because no light is reflected back the object appears black to the observer.
Describe how the reflection at a mirror is different from that at a non-mirror (this is a level 5-6 answer, give a reason with extra details).
The reflection at a mirror is different from a non-mirror because it has a smooth and shiny surface leading to light reflecting in uniform direction. Whereas when light reflects on objects that are uneven or contain particles it scatters in many directions resulting in dimmer reflection.
Outline why some things are transparent.
Transparent objects allow light to pass through because they don’t absorb or scatter it. Light rays are not blocked or reflected.
explain how the idea of modelling light as a wave is justified
When water waves pass through a small gap the waves spread out and diffracts. Light also spreads out and diffracts when it passes through a small gap. From this evidence we can model light as a photon.
Light can travel through empty space.
Light reaches us from the Sun
Light travels faster than anything else.
The speed of light is 300 000 000 m per second.
Light travels in straight lines
Lines can be seen through the path of a sunbeam or laser beam.
Light is a form of radiation.
Light radiates from its source, this is shown in diagrams by rays.
Light transfers Energy
Materials gain energy when they absorb light. For example, solar cells use the energy in sunlight to produce electricity.
Light travels as waves
Some effects of light are best explained by thinking of light as a stream of ‘energy particles’.
Examples of two objects that emit their own light
the sun
a burning candle
the nature of monochromatic light:
Different wavelengths are received by our eye and interpreted by our brain as different colours. Violet light has the shortest wavelength of 0.0004 mm and red light the longest wavelength of 0.0007 mm. White light is made up of a range of wavelengths. A light made up of only one colour is called monochromatic. One colour also implies one wavelength
Examples of two objects that are only visible because they reflect light from another source
a table
a rock
What evidence is there that light travels in straight lines
Light will keep travelling in a straight line until it hits something else and shadows are evidence of this. An object blocks light so that it can’t reach the surface where we see the shadow.
What happens to light when it strikes white paper?
The light reflects back all the visible wavelengths of light that shine on them, so the light still looks white to us.
What happens to light when it strikes black paper?
It is absorbed by the paper and does not reflect any back to our eyes.
How do waves of violet light defer from waves of red light?
Each colour is a different wavelength. Violet has the shortest wavelength, at around 380 nanometers (0.0004 mm), and red has the longest wavelength, at around 700 nanometers (0.0007 mm).
What is meant by monochromatic light?
Lights of a single wavelength and colour are called monochromatic light.
How fast does light travel?
300 000 000 m/s (3E10)
How long does light take to travel 1 km?
1 km → 1 000 m
velocity of light: 300 000 000 m s-1
distance: 1 000 m
time: ?
distance/velocity = time → 1 000/300 000 000 = 0.00000333333 s
Why can we call this ‘an instant’
Because when light is travelling such small distances, it happens so quickly that it’s unnoticeable to the human senses or typical time scales.
How fast is sound travelling in this example?
1 km → 1 000 m
velocity: ?
distance: 1 000 m
time: 3 s
distance/time = velocity → 1 000/3 = 333 m s-1
If an observer counts the gap between seeing the lightning flash and hearing the thunder as 10s, how far away was the flash?
velocity of sounds: 340 m s-1
distance: ?
time: 10s
velocity x time = distance → 340 x 10 = 3 400 m
Would this method work on another planet?
Other planet’s temperature
- speed of sound increases with temperature.
- On a colder planet, sound would travel more slowly.
Atmospheric pressure.
- Mars’ atmosphere is over 100 times thinner than that of Earth
- sound moves much more slowly through it, travelling at just 240 metres per seconds.
Determine how long it takes light to reach Earth from Mars?
54 600 000 km → 54 600 000 000 m
velocity of light: 300 000 000 m s-1
distance: 54 600 000 000 m
time: ?
distance/velocity = time → 54 600 000 000/300 000 000 = 182 s
How long does it take the signal to get to Mars and back according to the clip from the martian?
32 minutes
Why is this different to the answer you got above?
2 - The round-trip time versus the one-way travel time.
Differences:
#1 - The varying distance between Mars and Earth depending on their orbital positions.
The distance I used is 54,600,000 km.
At different times, Mars and Earth could be much farther apart (up to around 401 million km) or closer together.
The clip uses a specific moment when Mars is farther from Earth, making the one-way time much longer.
Minutes to seconds: 32 x 60 = 1 920 s
1 920/2 = 960 s
One-way signal time is 960 seconds.
Reflecting a situation when Mars and Earth are at a farther distance from each other in their orbits.
Problem solving
Check the end of the document.
Diffraction
where waves spread out to the edges when they pass through a gap or go past an object.
Diffraction is best when
the wavelength equals the size of the gap
An incandescent light bulb
produces visible light by incandescence.
An incandescent light bulb contains a thin wire filament made of tungsten. When electric current passes through the filament, it gets extremely hot and emits light.
Incandescence
occurs when something gets so hot that it glows.
A fluorescent light bulb
produces visible light by fluorescence.
LED light
stands for “light-emitting diode.”
Contains a semi-conductor, which gives off visible light when an electric current flows through it.
A neon light
produces visible light by electroluminescence.
neon or some other gas gives off light when an electric current passes through it.
-Neon produces red light.
-Krypton produces violet light
- Argon produces blue light.
Vapor light
A vapor light also produces visible light by electroluminescence
Reflection
when light bounces back from a surface that it cannot pass through.
Reflection may be regular or diffuse.
Regular/specular reflection
The surface is very smooth,
the reflected light forms a very clear image.
- reflect in uniform in one direction
Diffuse reflection
A rough surface,
the waves of light are reflected in many different directions, so a clear image does not form.
Transmission of light
occurs when light passes through matter. As light is transmitted, it may pass straight through matter or it may be refracted or scattered as it passes through.
Light is refracted (refraction)
it changes direction as it passes into a new medium and changes speed.
Scattering
occurs when light bumps into tiny particles of matter and spreads out in all directions.
Absorption
Light transfers its energy to matter rather than being reflected or transmitted.
- When light is absorbed, the added energy increases the temperature of matter
Transparent matter
transmits light without scattering it.
- Examples of transparent matter include air, pure water, and clear glass.
- You can see clearly through transparent object.
Translucent matter
is matter that transmits light but scatters the light as it passes through. - Light passes through translucent objects but you cannot see clearly through them because the light is scattered in all directions.
Opaque matter
is matter that does not let any light pass through it.
Matter may absorb light, reflects light, or do a combination of both.
