This page contains online questions only. Jot down
your answers and check them against the worked out answers at the end of
the page

**2.****
Examples of wave
equation calculations involving electromagnetic radiation**

You should know that all waves obey the
same **wave
equation**:

**
v = λ x f** where

**v** is speed in metres per
second, **m/s**,

for electromagnetic radiation
calculations, the speed in vacuum/air is taken as **
3.0 x 10**^{8} m/s

**λ** is wavelength in
metres, **m**

**f** is frequency in hertz,
**Hz** (per sec)

wave equation rearrangements:
**f = v / λ
**and**
λ = v / f**

**f = v / λ** and
λ = v / f

**Note **that you are not required to recall the value of the speed of
electromagnetic waves through a vacuum ...

.. it is very big, 'speed of light',
**v**,
is taken to be exactly **
3.0 x 10**^{8} m/s AND to
be used in all questions

Be able to do examples of
calculations using the wave speed formula and its rearrangements.

speed (m/s) = wavelength (m) x
frequency (Hz, s^{-1})

**
v = f x λ**
* **
f = v / λ *
λ = v / f**

You may also need:

**speed (m/s) = distance (m) /
time (s)**

**period (s) = 1 / f (Hz)**

**PLEASE , it is
much better to be able to rearrange the wave equation than use a triangle.**

**Q1**
A red light beam has a wavelength of 650 nm.

Calculate the frequency of red light
photons.

Worked out ANSWERS to the wave equation questions

**Q2**
A green laser light beam has a fixed frequency of 5.90 x 10^{14} Hz

Calculate the wavelength of the laser
light in m and nm.

Worked out ANSWERS to the wave equation questions

**Q3**
The time period of a electromagnetic radio wave is 5.0 x 10^{-5} seconds

(a) What is the frequency of the radio
wave?

(b) If the 'speed of light' is 3.0 x 10^{8}
m/s, calculate the wavelength of the radio wave in m.

(c) If the distance from the transmitting radio
station to your radio is 200 km, how long does it take the signal to reach
you?

Worked out ANSWERS to the wave equation questions

**Q4**
A wave of electromagnetic radiation has a wavelength of 25 cm

Calculate the frequency of the radiation.

Worked out ANSWERS to the wave equation questions

**Q5**
A scanning device sends out a pulse of microwave radiation that takes15
µs to detect an echo.

How
far away is the reflecting object? (you should know that 1
µs = 10^{-6} s)

Worked out ANSWERS to the wave equation questions

**Q6**
A radio station is broadcasting its programmes with a radio frequency of 104
MHz.

Calculate the wavelength of the radio
signal. (you should know 1 MHz = 10^{6} Hz)

Worked out ANSWERS to the wave equation questions

**Q7**
For radio astronomy, the shortest wavelength of radio waves that can pass
through the Earth's atmosphere is 100 m.

Calculate the maximum frequency of radio
waves that can be detected.

Worked out ANSWERS to the wave equation questions

**Q8**
A satellite is 75 km above the Earth's surface. (speed of light 3.00 x 10^{8}
m/s)

What is the shortest time that a
microwave signal would take to reach the satellite from the Earth's surface?

Worked out ANSWERS to the wave equation questions

**Q9**
A red light wave has a wavelength of 7.0 x 10^{-7} m. (speed of light
3.00 x 10^{8} m/s)

What is the frequency of the red light wave?

Worked out ANSWERS to the wave equation questions

Need Q using kHz, X-rays, gamma etc.
maybe a red-shift Q ?

INDEX of notes: Properties and
uses of
electromagnetic radiation

**
Keywords, phrases and learning objectives for electromagnetic radiation spectrum**

Be able to use and rearrange the wave equation for
electromagnetic radiation to perform calculations
and solve problems.

Know the formula relating speed m/s, wavelength
m and frequency Hz s^{-1}

i.e. v = f x λ
* f = v / λ *
λ = v / f

Use your
mobile phone in 'landscape' mode?

SITEMAP
Website content © Dr
Phil Brown 2000+. All copyrights reserved on Doc Brown's physics revision notes, images,
quizzes, worksheets etc. Copying of website material is NOT
permitted. Exam revision summaries and references to GCSE science course specifications
are unofficial.
INDEX of notes: Properties and
uses of
electromagnetic radiation