Physics (Light) Flashcards
Objects that can produce their own light
luminous objects
Objects that cannot produce their own light
non-luminous objects
Why can we see things that cannot produce their own light
Because light is reflected from them into your eyes
What makes objects look transparent?
The light travels through the object.
Why can we see the objects in the water tank?
Because the lights are able to travel through water and glass.
What is the space between Sun and the Earth?
Vacuum
How does light travel?
Light propagates in a straight line.
The formation of shadow is due to the _____________________.
rectilinear propagation of light
What causes an umbra?
If the light source is small
What is umbra?
full shadow
The edges of shadow(umbra) are__________
sharp
What causes a penumbra?
If the light source is large
What is penumbra?
partial shadow
The edges of shadow (penumbra) are__________
blurred
Draw the formation of the umbra and penumbra.
(Textbook page 6)
What is the reflection of light?
-light bounces back from a surface that it cannot pass through
-if the surface is very smooth, the reflected light forms an image
What is the transmission of light?
-Light pass-through matter
-may pass straight through the matter/be refracted or scattered(分散)by matter
What is the absorption of light?
-Light transfers its energy to matter rather than being reflected or transmitted by matter
-The temperature of the matter increases with the added energy
Draw the light interaction diagram:
textbook page 7
What is transparent matter?
Transparent matter transmits light without scattering it.
Give examples of transparent matter.
Air, pure water, and clear glass.
What is translucent matter?
Translucent matter transmits light but scatters the light as it passes through.
Why can’t you see clearly through translucent objects?
Because the light is scattered in all directions.
What is opaque matter?
Opaque matter does not let any light pass through.
Give examples of opaque objects.
objects made of wood and glass mirrors.
Why is a glass mirror considered opaque?
Because it reflects all of the light that strikes it.
What is the speed of light in km/h and m/s?
1,080,000,000 km/h or 300,000,000 m/s
How far does light travel in one second?
300,000 km every second
How many times can light travel around the Earth in one second?
About 7.5 times
Before the 17th century, what did people believe about the speed of light?
They believed that light was transmitted instantaneously.
Who was the first to measure the speed of light?
Ole Christensen Rømer
What did Ole Rømer’s experiment prove about light?
That the speed of light is not infinite.
In a thunderstorm, which comes first: lightning or thunder?
Lightning comes first, then thunder.
What can we conclude from thunder coming after lightning?
Light travels faster than sound.
What is the typical speed of sound in air?
1234 km/h
What is the typical speed of a rocket launch?
Between 9,000 to 12,600 km/h
What is the typical speed of a car on a highway?
110 km/h
What is the typical speed of a leisure stroll?
3 km/h
What is the typical speed of a snail?
0.048 km/h
What is a light-year?
A light-year is the distance that light travels in one year.
Why is a light-year used instead of kilometers in astronomy?
Because astronomical distances are so vast, using kilometers would involve very large numbers, making light-years more convenient.
How far is 1 light-year in kilometers?
About 10,000,000,000,000 km (10 trillion km)
How far is Proxima Centauri from Earth?
About 4.3 light-years
How long does it take for light to travel from the Sun to the Earth?
8 minutes
What is the distance from the Earth to the Moon in light-time?
1.3 light seconds
What is the distance from the Earth to Sagittarius A* (the center of the Milky Way)?
25,640 light-years
What does it mean when we say we see the Sun as it was 8 minutes ago?
Because light takes 8 minutes to travel from the Sun to Earth, we are seeing the Sun’s past image.
What does look at stars mean in terms of time?
We are seeing stars and galaxies as they were when their light left them, possibly millions of years ago.
The distance from Earth to Neptune is 4.621 billion km. How is this written in light-years?
Approximately 0.0005 light-years
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