Transcript Do you think light has a family?

Core Physics – Energy
Exam Date -
“On the air
waves”
L/O :- To understand way in which we use
electromagnetic waves for
communication
Quick Quiz - What do you remember
from last lesson?
• Write out the electromagnetic spectrum from longest to
shortest
• Which are the most dangerous EM waves? What can they
cause?
• What is the equation for working out the speed of a wave?
• What happens to a light ray when it travels from air through
glass? Why does this happen?
• What is diffraction?
• What are the 2 different types of wave? Give an example
• How do you work out the pay-back time for insulation?
• What are the pros and cons of wind energy?
• How does increasing the volume of a sound affect the wave?
Use what you
know to fill in
the crossword
about the
electromagnetic
spectrum
The Electromagnetic Spectrum
Each type of radiation shown in the electromagnetic spectrum has a
different wavelength and a different frequency:
High frequency,
_____ wavelength
Gamma
rays
X-rays
Low frequency, _____
(high) wavelength
Ultra violet
Visible
light
Infra red
Microwaves
Radio/TV
γ
Which of these
waves are used
for
communication?
Visible light
can be used
for optic
fibres and
photography
Microwaves will pass
easily through the
atmosphere so they are
used to send
information to satellites
for TV and phones
Radio waves are used
for TV and radio
Radio waves are used for communication
There are 3 types of radio waves
• Short wave (3,000–30,000 kHz) – Only travels
short distances but very clear (e.g. FM radio)
• Medium wave (300 kHz to 3 MHz) – travels
further than short wave but not as clear
• Long wave (3 MHz +) – Can travel a long way
but less defined
Why does your FM
radio not work
when you go into a
multi-storey car
park??
Why do you think
Medium wave radio
can be heard in
valleys but FM
cannot?
Long wave radio
EM waves (like radio) can also be diffracted …
Diffraction depends on frequency…
A high frequency (short wavelength)
wave doesn’t get diffracted much – the
house won’t be able to receive it…
28/03/2016
A low frequency (long wavelength) wave
will get diffracted more, so the house
can receive it…
28/03/2016
Other ways of transmitting information
Microwaves are used by satellites because
they can pass through the Earth’s
atmosphere:
Microwaves are used for
mobile phone networks
and Satellite TV
28/03/2016
Artificial Satellites
Geostationary orbits:
These satellites have a
high orbit so they can
orbit at the same speed
as the earth. This means
they remain at the same
point in the sky
Used for communication
28/03/2016
Low polar orbits:
These have low orbit so they
sweep around the earth
(usually every 24 hours)
Used for Weather
Transmitting information
Although E-M radiation travels in straight lines, we can send infra-red and
light signals around a curved path using an optical fibre:
Optical fibres have two main advantages: they can send more information
compared to electrical cables of the same diameter and with less signal
weakening.
Investigation – What angle does total
internal reflection happen at in glass?
28/03/2016
The critical angle for class is 42©C
How accurate were your results?
Finding the Critical Angle…
1) Ray gets refracted
2) Ray still gets
refracted
3) Ray still gets
refracted (just!)
4) Ray gets internally
reflected
28/03/2016
THE CRITICAL
ANGLE
28/03/2016
Endoscope’s are used in hospitals to look inside the body without surgery.
The optic fibre provides the light source for the camera
What have you learnt?
• Can you list the parts of the
electromagnetic spectrum used for
communication ?
• Can you explain why microwaves are used
for satellite TV?
• Can you explain how optical fibres work?