4-9 Knowing more 4.3 (4.3)

• Natuurkunde
• Middelbare school
• havo, vwo
• Leerjaar 2

The speed of light (knowing more 4.3)

Lesson goals:

- Understand and explain how 

    fast light moves

- Understand and explain what 

    a light-year is

- Make calculations with 

     the concept of light-years

The speed of light

- In one second light travels a distance of 300 000 km

- With the vast distances in space, light needs time to travel

For example:

The distance from the sun 

to the earth is 150 miljoen km, 

and sunlight needs 8,3 minutes 

to reach the earth.

Light of the stars

- The light of the closest star 

   takes 4 years before reaching the 

  earth.

- Light from most stars that we see 

   is light that has been traveling for several decades before they reached the earth.

- The best telescopes can see light that has been traveling for 

    13 billion lightyears.

Mars rover

The distance between Earth and

Mars varies between 56 million

and 400 million km.

At the greatest distance between these planets, it takes 22 minutes to send a signal to mars, and therefore to make contact with the mars rover.

(This is because radio waves also move with the speed of light)

Light-year

- Due to the vast distances in space, 

meters and kilometers are inconvenient units to use.

For example, the closest star is 

40 500 000 000 000 km from the earth

THEREFORE - we use light-years as a measure of distance in space. (It is the distance traveled by light in one year)

1 light-year = 9,5 trillion km

What is the speed of sound?

1. 340 m/s
2. 300 000 km/s

How long does it take for the light of the closest star to reach earth (don't consider the sun)?

1. 7 seconds
2. 8,3 minutes
3. 4 years
4. 150 years

Is a light-year a unit of time or a unit of distance?

1. time
2. distance

Why do we use the unit of light-years?

Show with a calculator that a light-year is
9,5 trillion km (make a photo of your calculation)

Now do the following activities 

on p. 180

58 up to 60

No discussion

8 minutes

When you are done, research the question 'how large is the universe' ...

Conclusion

• Speed of light = 300 000 km/s
• Distances in the universe are so vast that we use light-years as a unit of distance. One light-year = 9,5 trillion km
• The formula of velocity is useful when making calculations

ps

1 trillion = 1 000 billion = 1 000 000 million = 1 000 000 000 thousand