Waves Flashcards
Complete the sentence: Waves transfer __________ without transferring ____________.
energy, matter
What is the amplitude of a wave?
The maximum displacement of a point on the wave from its undisturbed position.
What is wavelength?
The distance between the same point on two adjacent waves.
What is the frequency of a wave?
The number of complete waves passing a certain point per second. Measured in hertz.
What is the period of a wave? State the equation.
The amount of time it takes for a full cycle of the wave to pass a point.
Period (s) = 1/ Frequency (Hz)
What is a transverse wave?
A wave where the oscillations are perpendicular to the direction of energy transfer.
What is a longitudinal wave?
A wave where the oscillations are parallel to the direction of energy transfer.
What is the equation linking frequency, wave speed and wave length?
Wave speed (m/s) = Frequency (Hz) x Wave length (m)
What piece of equipment can be used to measure the speed of sound?
Oscilloscope.
Give a method for measuring the speed of sound.
- Set up the oscilloscope so the detected waves at each microphone are shown as separate waves.
- Start with both microphones next to the speaker, then slowly move one away until the two have aligned on the display, but have moved exactly one wave length apart.
- Measure the distance between the microphones to find one wavelength.
- Use the formula wave speed = frequency x wavelength to find the speed of the sound waves. The frequency is whatever you set the signal generator to.
What piece of equipment can you use to measure the speed of water ripples?
A lamp.
Give the method for measuring the speed of water ripples.
(Using a signal generator attached to the dipper of a ripple tank, you can create water waves at a set frequency)
- Dim the lights and turn on the lamp. A wave pattern can be seen made by the shadows of the water crests on the screen below the tank.
- The distance between each shadow line is equal to one wavelength. Measure the distance between shadow lines that are 10 wavelengths apart and then divide by 10 to find an average wave length.
- If you’re struggling take a photo of the shadows and ruler.
- Use Wave speed = frequency x wavelength to calculate the speed of the waves.
Give the method for creating a wave on a string.
- Attach a signal generator to a vibration transducer. Attach a piece of string to the vibration transducer, a pulley and a weight.
- Adjust the frequency setting on the signal generator to change the length of the wave created on the string. Keep adjusting until a clear wave appears on the string.
- Measure the wavelength of the wave. To do this, measure the length of all the half-wavelengths on the string, then divide by the total number of half-wavelengths to get a mean. Then double to get a full wavelength.
- The frequency of the wave is what the signal generator is set to.
- To find the speed, use wave speed = frequency x wavelength.
Complete the sentence: All waves can be a___________, t________ or r____________.
Absorbed, transmitted, reflected.
What are the three things that can happen when a wave arrives at a boundary between two different materials?
- The waves are absorbed by the material - energy is transferred to the material’s energy store.
- The waves are transmitted - carry on travelling through the material (often refracted).
- The waves are reflected - bounce off in a different direction.
What is the rule involving the angle of incidence and angle of reflection?
Angle of Incidence = Angle of Reflection
What is the angle of incidence?
The angle between the incoming wave and the normal.
What is the angle of reflection?
The angle between the reflected wave and the normal.
What is the normal in a ray diagram?
An imaginary line that’s perpendicular to the surface at the point of incidence. Usually shown as a dotted line.
What is the difference between specular reflection and diffuse reflection?
Specular reflection - happens when a wave is reflected in a single direction by a smooth surface.
Diffuse reflection - happens when waves are reflected by a rough surface and are scattered in lots of different directions (angle of incidence = angle of reflection still applies)
What is refraction?
When light waves are bent when they enter a new media/material.
What does the size of refraction depend on?
How much the wave speeds up or slows down (density).
What direction does a wave bend when it crosses a boundary and slows down?
Towards the normal.
What direction does a wave bend when it crosses a boundary and speeds up?
Away from the normal.
What happens to the frequency of a wave when it is refracted?
Stays the same.
When a wave is refracted in a material of high density does it slow down or speed up?
Slows down.
What is the optical density of a material?
A measure of how quickly light can travel through it. The higher the optical density, the slower light travels through it.
Explain how to construct a ray diagram to show refraction.
- Draw the boundary between the two materials and the normal.
- Draw an incident ray that meets the normal at the boundary.
- Draw the refracted ray on the other side of the boundary. If the second material is optically denser than the first, the refracted ray bends towards the normal, so is smaller than the angle of incidence.
When doing light experiments, why does the room have to be dim?
So that you can clearly see paths of the rays of light.
Give the method for using transparent materials to investigate refraction.
- Place a transparent rectangular block on a piece of paper and trace around it. Use a ray box or laser to shine a ray of light at the middle of one side of the block.
- Trace the incident ray and mark where the light ray emerges on the other side of the block. Remove the block and draw a straight line to join up the incident ray and the emerging point to show the path of the refracted ray through the block.
- Draw the normal at the point where the light ray entered the block. Use a protractor to measure the angle between the incident ray and the normal and then the angle between the refracted ray and the normal.
- Repeat this experiment using rectangular blocks made from different materials, keeping the incident angle the same throughout.
How could you make the required practical investigating refraction through different transparent materials more accurate?
- Use a laser instead of ray box to produce thin rays of light.
Complete the sentence: How light reflects depends on the _____________ of the surface.
smoothness
Give a method for investigating how different surfaces reflect light.
- Take a piece of paper and draw a straight line across it. Place an object so one of its sides lines up with this line.
- Shine a ray of light at the objects surface and trace the incoming and reflected light beams.
- Draw the normal at the point where the ray hits the object. Use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table. Make a note of the width and brightness of the reflected light ray.
- Repeat this experiment for a range of objects.
What type of waves are electromagnetic waves?
Transverse.
What are electromagnetic waves?
Transverse waves that transfer energy from a source to an absorber. They are vibrations of electric and magnetic fields.
Can electromagnetic waves travel through a vacuum?
Yes.
Give the order of electromagnetic waves with increasing frequency and decreasing wave length.
Radio waves
Micro waves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
Which electromagnetic wave has the highest frequency?
Gamma rays.