P11 Wave Properties Flashcards
Transverse waves
The oscillations are perpendicular to the direction waves transfer energy. All electromagnetic waves are transverse waves.
e.g. light wave. Radio wave, microwave, ripples on the surface of water, waves on a string, seismic S-waves
Longitudinal waves
The oscillations(compressions and rarefactions) are parallel to the direction waves transfer energy
e.g. sound wave, ultrasound wave, infrasound wave
Peak
Top of a wave
Trough
Bottom of a wave
Amplitude
The amplitude of a wave is the maximum displacement of a point on the wave from its undisturbed position. The bigger the amplitude of the waves, the more energy the waves carry.
Wavelength
The distance from a point on the wave to the equivalent point on the adjacent wave.
Frequency
Number of waves past a fixed point per second
Period
Time taken for each wave to pass a fixed point
Period equation
1/frequency(hertz)
Wave speed equation(for waves of constant frequency)
Wave speed = frequency x wavelength
What is a ripple called in a ripple tank
Each ripple in a wave is called
a wavefront because it’s the front of each wave as it travels across the water surface.
Refraction
Change of direction in which plane waves(straight waves) are travelling when they cross a boundary between one medium and another medium. .
What happens at a boundary between two different materials?
Waves can be transmitted or absorbed.
e.g. Light is transmitted by ordinary glass.
Food is heated in microwave ovens.
How to produce sound waves
Vocal cords vibrate and produce sound waves when you speak.
Any object vibrating in air makes the layers of air near the object vibrate, which makes the layers of air near them vibrate. The vibrating object pushes and pulls repeatedly on the air
This sends out vibrations of air in waves of compressions and rarefractions. When the waves reach the ears, they make eardrums vibrate in and out so they hear sound.
Speed of sound waves
It increases with increasing temperature and is 340m/s at 15C
Where are all angles measured?
All angles are measured between the ray and the normal.
Angle of incidence
Angle a ray comes in at
When light waves travel from a faster material to a slower one…
The light refracts and bends towards the normal
When light waves travel from a slower material to a faster one…
The light refracts and moves away from the normal
How does refraction affect frequency?
In refraction, the frequency of the waves doesn’t change.
Optical density
How dense it is for light
Dispersion of light in a prism
Red light refracts the least, but blue and purple light reflects the most
Optical density
How dense it is for light to travel
Normal
90 degrees to the boundary
Frequency=
Energy in wave
Frequency
Number of oscillations in one second
How can waves transfer energy?
Waves transfer energy and information without a net motion of the medium through which they travel(wave material moves up and down bit doesn’t move along). Waves transfer energy without transferring matter
Wave speed in a ripple tank required practical
1)To measure the wavelength, take a photo of the waves to count how many there are,
measure the length of the whole thing and wavelength = total distance/number of waves.
2)To measure the frequency, use a stopwatch and count how many waves pass a certain point in 60s and frequency = number of waves/60 seconds
Wave speed in a ripple tank required practical(equipment)
Signal generator(changes frequency)
Ripple tank
Motor
Lamp
Angle of incidence=
Angle of reflection
Reflection practical equipment
Ray box, slip, protractor, mirror
Reflection(practical) experiment
1)Draw a straight line where the mirror will be.
2)Draw where you’ll aim the light with the normal the direct 90 degrees above it.
3)Connect the lines and use a protractor draw 9 sections 10 degrees apart.
4) Shine the light on the marked lines for light to come out the other side and draw lines where the light comes out. The lines should come out at the same angles as the lines on the other side.
Refraction practical
1)Draw a straight line for the boundary.
2)Draw where you’ll aim the light(with the normal 90 degrees above it).
3)Measuring between the normal and incident ray, draw lines 10 degrees apart.
4)Place a light at the normal, refraction doesn’t occur with a glass block at the normal.
5)Mark where the light goes and remove the block to measure the angles of refraction using a protractor from the angles marked out at the start from the normal. The angles of incidence aren’t the same as the angles of refraction.
Uses of waves
To transfer energy
To transfer information
Electromagnetic waves
Waves which can travel through a vacuum at the same speed of 300000 km/s without a medium
Mechanical waves
Vibrations that travel through a medium(a substance)
Observing wave motion through a spring model
1) Tie a ribbon to the middle of the rope. Moving end of the rope up and down, you’ll see the waves move along the rope but the ribbon doesn’t move along the rope, it just moves up and down(a transverse wave. The ribbon vibrates/oscillates and when the ribbon is at the top of a wave, it’s said to be at the peak/crest of the wave.
2)
Repeating a test with the slinky: if you push and pull the end of the slinky, you see a longitudinal wave with areas of compression(coils squashed together) and areas of rarefaction(coils spread further apart) moving along the slinky.
Examples of mechanical waves
Sound waves, water waves, waves on springs
Examples of electromagnetic waves
Light waves, radio waves and microwaves
Measuring the speed of sound in air
1) Stand on opposite sides of a field at a measured distance apart, as far apart as possible but within sight of each other.
2) If your friend bangs two cymbals, you’ll see them crash straightaway, but won’t hear them straightaway. The crashing sound is delayed as sound travels slower than light.
3) Use a stopwatch to time the interval between seeing the impact and hearing the sound. Repeat the test seceral times to get an average value of the time interval.
4) Calculate the speed of sound in air = distance/time taken
How is amplitude affected as waves travel through a substance?
The amplitude of the waves gradually decreases as the substance absorbs some of the waves’ energy
What happens to waves not absorbed by a substance?
Waves not absorbed by the substance they’re travelling through are transmitted by it
Reflection in a ripple tank
Plane(straight) /incident waves in a ripple tank, produced by dipping the long edge of a ruler in water,are reflected from a straight barrier at the same angle to the barrier as their incident waves since speed and wavelength don’t change on refraction.
What happens to plane waves crossing a boundary between two different materials?
They’re refracted unless they cross the boundary at normal incidence(perpendicular to the boundary).
Why does refraction occur at a boundary between two different materials!
Since the speed and wavelength of waves change at the boundary
Speed of sound waves in air
340m/s
Echo
Reflection of sound that can be heard(from a smooth/hard surface).
The delay before an echo is because the sound waves travel to the wall and back before hearing the echo.
Speed = 2d(distance to wall and back)/time delay
Sound waves
Vibrations that travel through a medium
Investigating waves(required practical).
1) Use a ripple tank for water waves. A ruler can create plane waves travelling towards one end of the ripple tank and use a stopwatch to measure the time for a wave to travel from one end to another. Measure the distance the waves travel in this time and use the equation = speed = distance/time. Observe the effect of moving the ruler up and down on the speed of the waves.
2) Use a stretched spring for waves in a solid. The oscillator should send waves along the spring, use a frequency generator to adjust the frequency of the oscillator until there’s a single loop on the spring. Its length is half the length of one wavelength. The vibrating string sends sound waves at the same frequency into the surrounding air. Note the frequency of the oscillator, find the length of a single loop and calculate the wavelength of the waves(2 x the length of a single loop), calculate the speed of the waves on the string using the equation(wave speed = frequency x wavelength), but increase the frequency to obtain more loops on the spring and see if the wave speed is the same.
3) Use a signal generator and loudspeaker for sound waves.
What happens to a substance which a wave travels through?
The substance itself doesn’t travel
Why are the sides of a ripple tank sloped?
Slopes prevent reflection at side of tank
Radiation dose
A measure of the risk of harm to a person from exposure to radiation
