3. Waves Flashcards
What do waves do
Waves transfer energy and information without transferring matter
Define frequency and give its units
● The number of waves passing through a point per second.
● Hz (hertz)
Define wavelength
The distance between two adjacent
peaks on a wave
Define amplitude
● The maximum displacement of the
wave from its equilibrium position.
● The distance between the centre of
the wave and a peak
What is meant by the period of the
wave?
The length of time it takes for ONE FULL WAVE to pass through a point
How can you calculate the wave speed?
● Wave speed (measured in metres per second) is equal to the product of the wavelength and the frequency of the wave.
● Wave velocity= f ×λ
State an equation linking frequency and
period of a wave
frequency (Hz) = 1/ time period
f = 1/T
What is a longitudinal wave? Give some
examples
● Vibrations are parallel to the direction of
energy transfer(wave)
● Examples include sound waves and
earthquakes (seismic waves)
What is a transverse wave? Give some
examples.
● A wave with oscillations that are perpendicular ( 90 degrees) to the direction of energy transfer. ● Examples include electromagnetic waves
Explain what is meant by “the Doppler effect”
Apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer. When a wave source is moving towards the observer, observed frequency increases and observed wavelength decreases; when a wave source is moving away from the observer, observed frequency decreases and observed wavelength increases since v= f ×λ and speed in constant
At what speed does an electromagnetic
wave travel in a vacuum?
3 x10^8 m/s
What types of waves are electromagnetic waves?
Transverse
What do electromagnetic waves
transfer?
Energy and Information
What are the four common properties of all electromagnetic waves?
· They are all transverse waves
· They all transfer energy or information
· They all travel at the speed of light in vacuum
· They all can be reflected, refracted or diffracted
Which part of the electromagnetic spectrum has the longest wavelength?
Radio waves
Order the electromagnetic spectrum from
the highest frequency to the lowest
frequency
Gamma rays, x-rays, ultraviolet, visible
light, infrared, microwaves and radio
waves
What are the colours of the visible light spectrum?
Red, Orange, Yellow, Green, Blue, Violet
a. Which colour has the highest frequency?
b. Which colour has the lowest frequency?
c. Which colour has the lowest wavelength?
d. Which colour has the highest wavelength?
a. Violet
b. red
c. violet
d. red
What are the uses of radio waves?
● For communication through radio
● Used for satellite transmissions
What are microwaves used for?
● Cooking in microwaves ovens
● Communications
● Satellites
Which part of the electromagnetic
spectrum is used in cooking, thermal
imaging and television remote controls?
- Infrared
Give examples of uses for visible light?
● Allows us to see (used for vision)
● Photography
● Optical Fibres
(endoscope,communication)
What part of the electromagnetic
spectrum is used to for security marking
and in fluorescent lamps?
Ultraviolet
What are some uses of x-rays?
● Scanners at airports
● Medical x-ray machines
What are the uses and disadvantages of
gamma rays?
● Used to sterilise food and medical equipment
● Used in cancer diagnosis
● Can cause mutations or damage to body cells. This could lead to death.
What are the disadvantages of
microwaves?
They can cause heating of internal
tissues in the body
Which part of the electromagnetic
spectrum is used in TV remotes and can
also cause skin burns?
- Infrared
Does the danger that is associated with
electromagnetic waves increase with
frequency or with wavelength?
With frequency
What are the dangers of excessive
exposure to ultraviolet?
You could damage your eyes and the
cells on the surface of your skin. This
could lead to skin cancer or eye
conditions
What is the normal (in terms of reflection
and refraction)?
A vertical imaginary line which is
perpendicular to the boundary
What happens when light is reflected off
a boundary?
It is reflected (bounces) off a smooth flat
surface so that the angle of incidence
(the angle it comes in at) is the same as
the angle of reflection (the angle it leaves
at).
What happens when light is refracted
while passing through 2 different media?
● The light changes speed and direction in the new
medium
● If the new medium is more dense, the light will
travel slower and bend towards the normal
● If the new medium is less dense, the light will
travel faster and bend away from the normal
State an equation linking angle of incidence, angle of
refraction and refractive index
n = sin(i)/sin(r)
n= refractive index i= angle of incidence r= angle of refraction
What is the critical angle?
The angle of incidence which causes the angle of
reflection to be 90 degrees so that that the light
refracts onto the boundary.
State an equation linking critical angle
and refractive index
n = 1/sin(c)
What is total internal reflection?
When light is trying to pass from a less dense
medium to a denser medium, it can be reflected
back to the less dense medium if the angle of
incidence is larger than the critical angle between
two media.
This reflection is called Total Internal Reflection
State two uses of total internal reflection
- Endoscopes
- Periscopes
- Optical Fibres
- Cat Eye Reflectors
- Shining of Diamonds
If light hits a boundary at 90 degrees to
the surface, will the light refract?
No, it will not
Is light an example of a transverse or longitudinal wave?
Transverse
-
-
What is the law of reflection
Angle of incidence = angle of reflection
What is the law of refraction
All waves can be refracted, which is when the speed of a wave changes when it enters a new medium
What happens if a wave enters a denser medium
Its speed decreases and it bends towards the normal
What happens if a wave enters a less dense medium
Its speed increases and it bends away from the normal
What happens to the velocity of a wave when refraction occurs
In all cases, the frequency stays the same but the wavelength changes. As a result, the velocity must change.
Sound waves are …… waves and can be reflected and refracted
Longitudinal
The range of audible frequencies for a healthy human ear is ……..
20 Hz to 20,000 Hz.
How can you measure the speed of sound in the air
- To measure the speed of sound in air, you can make a noise at a known, large distance from
a solid wall and record the time for the echo (reflected sound) to be heard, then use
speed = distance/time, where distance is 2 x length - taking into account the fact that the
sound had to go there and back - An oscilloscope connected to a microphone can be used to display a sound wave and find
its frequency and amplitude.
The greater the amplitude of a sound wave, the …… it is.
Louder
The greater the frequency of a sound wave, the …..
Higher its pitch
