To do and to answer - this checks your understanding!!!
Is light a wave?
Read Textbook Section D: Radiation and waves. Stop at What
is the medium?
Use the information in the first paragraph to answer these
questions:
1 a Write down two sources of light given in the text.
b Write down two detectors of light given in the text.
c What are the three things that could happen to light
when it hits something?
2 Which scientist thought light was a stream of particles?
3 Which scientist thought light was a wave?
On the paragraph below (which is reprinted from the textbook):
4 a Underline two wave properties which are things that also
happen with streams of particles.
b With a different colour, underline all the pieces of
equipment that Young used for his experiment.
c Draw a box around the words that tell you what you
should see on the screen.
d Using a wiggly line underline the word that tells you what
property of waves produces this pattern. (Hint: It happens
to water waves too.)
People have always wondered what light really is. For a long time, scientists
were
unsure how best to think about light.
Two of the wave properties –
reflection and refraction – do not really provide conclusive
evidence either
way. A wave or a stream of particles would also be reflected by a
barrier.
And both would be refracted at a boundary where their speed changed.
The
evidence that convinced scientists it was useful to think of light as a wave
came
from an experiment carried out by Thomas Young in 1801. Young used a
narrow slit to
produce a fine beam of light from a bright lamp.
He shone
this on a slide with a double slit (two parallel clear lines on a black slide).
On
a screen about 1 metre away Young saw a pattern of bright and dark
vertical lines. To
understand this, look back at the photograph on page 239
(of the textbook) of
interference in a ripple tank. With water waves, there
are lines of disturbance and lines
of calm water. If the same happens with
light, you would expect lines of brightness and
lines of dimness, spreading
out behind the double slit. On the screen, you should see a
series of bright
and dark patches.
