physics topic 6 Flashcards
describe transverse waves
Vibrations are perpendicular to the direction of energy transfer.
Electromagnetic waves travel at what speed
at the speed of light
(3x10^8m/s)
give examples of transverse waves
Water waves,
electromagnetic (light) waves
describe Longitudinal waves:
Vibrations are parallel to the direction of energy transfer.
what are some examples of longitudinal waves
Sound waves and a type of seismic (P) wave.
what is wavelength (λ)
distance from one point on a wave to the same
point on the next wave.
what is Amplitude (m)
maximum displacement from its undisturbed position.
what is Frequency (Hz)
waves per second.
what is Period (s)
the time taken to produce one complete wave.
give the practical for measuring the speed of sound in air
- Student A hit two cymbals together and student B started a stopwatch.
- When student A heard an echo she hit the cymbals together again.
- Student B stopped the stopwatch after timing 5 echoes.
- Calculate an average time for the echoes and ÷ by 2 (there and
back) - Use a measuring tape to work out the distance between students and wall
- Speed = Distance / Time
why does sound move faster through solids
- Sound needs particles to travel
- In a solid, particles are very close together
- So sound is fastest through a solid
describe the Ripple tank practical (investigating waves)
Frequency
* use a stopwatch
- count the number of waves passing a point in 10 seconds
- Number of waves / 10 seconds = average frequency
Wavelength
- use a camera to freeze the image
- use a metre rule to measure the distance between 10 waves
- divide distance by 10 to determine average λ
Velocity
* use v=fλ
what happens when a sound wave travels from one medium to another e.g. air to water
the frequency remains the same.
The sound wave will travel faster in water than air.
what happens if if the frequency remains the same, as velocity increases
wavelength must also increase proportionally.
what is the Human hearing range
20Hz and 20,000Hz (20kHz). Anything above this is
called ultrasound
what is anything’s above 20,000Hz called
ultrasound
describe how Ultrasound waves are used for detection
Ultrasound waves are partially reflected
when they meet a boundary between
two different media.
The time taken for the reflections to meet
a detector can be used to determine how
far away the boundary is.
describe some medical uses for ultrasound
- Pre-natal scanning
- Imaging (a named body part).
why is ultrasound safe to use
Ultrasound does not damage (human) cells
describe Echo
location/SONAR
Echo location or SONAR uses high frequency sound waves to detect objects in deep water and measure water depth
what waves do earthquakes produce
Earthquakes produce P and S waves.
describe P waves
fast longitudinal; travel at different speeds through solids and liquids.
describe S waves
slower transverse; cannot travel
through liquids.
what can p waves and s waves lead us to understand about the earth
This information can be used to determine the size, density and state of the Earth’s structure. As S waves do not penetrate the outer core, they can not be used to determine whether the inner core is liquid or solid.
The study of seismic waves provided new evidence that
led to discoveries about what
parts of the Earth which are not
directly observable.
give examples of transfer of energy by electromagnetic waves
Heater - Infra red waves- Detected by heat sensors in the hand
Torch - Visible light waves - Detected by cells in the retina
Radio transmitter - Radio waves -Detected by the aerial in the radio
what does The hazard from high energy radiations depend on
depends on the dose - measured in Sieverts.
what harm can Ultra violet waves cause
Ultra violet waves can cause sunburn, ageing of the skin and skin cancer.
what harm can X rays and gamma rays cause
X rays and gamma rays are ionising radiations that can cause mutations of genes which could result in cancer.
list the type of electromagnet waves from Low frequency long
wavelength to High
frequency short wavelength
radio
microwave
infrared
visible
ultraviolet
tanning beds
x rays
gamma rays
describe the application and Suitability of radio waves
Application - Television and radio
Suitability - Travels long distances
describe the application and Suitability of microwaves
Application - Satellite communications. Cooking food
Suitability - Travel through atmosphere; vibrates water molecules causing them to heat food
describe the application and Suitability of Infrared waves
Application - Electrical heaters, cooking food, infrared cameras
Suitability - Heat energy transfer
describe the application and Suitability of Visible waves
Application - fibre optic communications
Suitability - Travel through optic fibres and carry information
describe the application and Suitability of ultraviolet waves
Application - tanning beds
Suitability - Skin reacts to UV light causing tanning
describe the application and Suitability of X-rays
Application - Medical imaging and treatment
Suitability - Pass through soft tissue, penetrate materials to different extents so can produce image
describe the application and Suitability of Gamma rays
Application - Medical imaging and treatment
Suitability - Kill tissue; tracers can produce images of internal organs.
what happens to light when it shines on object
Absorption, transmission and reflection
Absorbed light is changed into what
heat energy
why does A red object appears red in white light
because it only reflects the red
wavelengths of light, all other colours are absorbed.
what do Filters do
Filters only allow light of certain
wavelengths through (transmit). The rest are absorbed
how do colour filters work
Colour filters work by absorbing certain wavelengths
(and colour) and transmitting other wavelengths
(and colour).
what happens if If all wavelengths are reflected
the object appears white
what happens if all wavelengths are absorbed
the object appears black
Light reflecting off a smooth, flat surface produces what
specular reflection.
When light reflects off a rough surface produces what
diffuse reflection
what does it mean if something is Transparent
a material that allows objects
behind it to be seen clearly as if nothing was in the way.
what does it mean if something is Translucent
a material that allows objects to
be seen through them but not as clearly or
sharply as a transparent material.
what does it mean if something is Opaque
a material that may or may not
allow light through to the object behind. It
would be difficult to tell what object is behind
an opaque material.
what is the law of reflection
Angle of incidence (i) =
angle of reflection (r)
why does Refraction of electromagnetic waves occur
because the wave changes speed when it enters a substance of different density.
why do we have a spectrum of colour
Different wavelengths of light are diffracted by different amounts, resulting in a spectrum of colour
describe the Light Required practical
- Draw around the glass block on a piece of paper
- Use the ray box to shine a ray of light through the glass block
- Mark the ray of light entering in and emerging from the glass block
- Join the points to show the path of the complete ray through the block
- Draw a normal line at 90 degrees to the surface
- Use a protractor to measure the angle of incidence and refraction
- Increase the angle of incidence in 100 intervals – from 100 - 700
Increase accuracy:
Repeat and calculate a mean
Use a laser
Explain refraction using wave front diagrams
- Different parts of the wave front enter the glass at different times
- the velocity / speed (of light) is less in glass
- (so) one part of the wave front changes speed before other parts
how do black surfaces interact with infra red waves
Black surfaces absorb infrared
waves better than white or
shiny surfaces.
Black surfaces also emit infrared radiation quicker than light coloured surfaces
why are Petrol storage tankers are painted white or polished
reflect the suns infra red
heat waves.
describe the IR Radiation and absorption required practical
- Get a hollow metal cube with 4 faces; matt black, shiny black, matt white, shiny silver
- Fill cube with boiling water and measure temperature of water with a thermometer
- Measure temperature of one of faces by placing infrared thermometer 20cm away
- Repeat with other 3 faces
- Record results
Safety:
complete the investigation standing up use (slightly) cooler water do not touch the hot cube
Applying radiation to electrons can do what
can excite them – move up an
energy level (excitation)
what causes the release of radiation
If electrons move down an
energy level, they release the
radiation (de-excitation)
how do radio waves work
- Alternating current (AC) passed through a radio transmitter
- Oscillating electrons produce a radio wave
- Antenna/ aerials absorbs radio waves
- Electrons vibrate (in the aerial)
- Inducing an alternating current (in the aerial circuit)
- With the same frequency as the radio wave
Convex lenses (converging) produces what image
produce real or virtual images.
Concave lenses (diverging) produces what image
produce virtual images.
what is a Real image
A Real image is an image formed where the light rays are focused.
what is a Virtual image
A Virtual image is one from which the light rays appear to come from but don’t actually come from that image e.g. a mirror reflection)
Explain the difference between a real image and a virtual image.
- real image can be put on a screen
- virtual image cannot be put on a screen / film
- virtual image is imaginary
- real image is formed where (real) rays cross / converge
allow real image has light travelling through it - virtual image is where virtual / imaginary rays (seem to) come from
- virtual image formed where virtual rays intersect / cross
what is A perfect black body
A perfect black body absorbs all of the radiation and also emits all radiation
describe how waves heat up the earth
Short wavelength radiation from the sun
passes through the Earth’s atmosphere
Re-radiated as long wavelength radiation.
Absorbed by greenhouse gasses and reflected
back to Earth heating it up; global warming.
how is a body kept at constant temperature
Constant temperature: Rate of radiation emission = Rate of radiation absorption
how does the temperate of a body increase
The temperature of a body increases when the body absorbs radiation faster than it
emits radiation.
