Wave experiments

Question 1

how does a ripple tank work

Answer 1

1. A ripple tank is a shallow tray of water and in the water there is a vibrating bar
2. The bar is connected to a power pack
3. When the bar vibrates, it creates waves across the surface of the water
4. Above the ripple tank, we have a lamp and below the tank we have a sheet of paper
5. When light shines through the water, it produces an image of the waves on the paper

Question 2

why do we use a mobile phone to record the waves

Answer 2

allows us to play back the recordings at different speeds or to freeze the image completely

Question 3

ripple tank method

Answer 3

Equipment list - ripple tank, water, camera, ruler, power source

1. Check that the bar that will create the waves is only just touching the water
2. Turn on the light so that we can see the waves appearing as moving lines under the tank
3. Turn on the motor and wait a few seconds for the waves to start, then take a photo or freeze the video
4. Measure the length of 10 waves then divide it by 10 to find the wavelength
5. To find the frequency of the waves, count the number of waves that pass a point over a 10 second period and divide by 10
6. Now that we know the wavelength and frequency, we can use this to find the wavespeed

Question 4

alternative method to find wavespeed

Answer 4

select a wave and measure the time it takes to move the length of the tank
- calculate the speed by dividing the distance travelled by the time taken

Question 5

Investigating waves in a solid method

Answer 5

equipment- metal bar, datalogger, two microphones, hammer

1. suspend the metal bar and attach the microphones to each end and connect them to the datalogger using wires
2. measure the distance between the two microphones
3. Start the datalogger and tap the bar to make a sound
4. Distance/time = speed of the sound through a solid

Question 6

what does a signal generator do

Answer 6

allows us to change the frequency of vibration of the string

Question 7

where do we find standing waves

Answer 7

• musical instruments like guitars

Question 8

waves in a solid method

Answer 8

1. measure the wavelength of the standing wave from the wooden bridge to the vibration generator using a ruler
2. use this to calculate the speed of the wave
   - to find frequency, read it off the signal generator

Question 9

how to calculate the wavelengths if we increase the frequency

Answer 9

divide the total length by the number of half wavelengths the. divide by 2

Question 10

investigating how much infrared is emitted or absorbed (method)

Answer 10

1. Fill a leslies cube with hot water
2. Point a an infrared detector at each of the four surfaces and record the amount of infrared emitted
3. Results should show that the matt black surface emits the most infrared radiation, then the shiny black, then the white, then shiny metallic

Question 11

what are each of the surfaces on a leslie cube

Answer 11

• a shiny metallic surface
• a white surface
• a shiny black surface
• a matte black surface

Question 12

why is it important to keep the same distance between the leslies cube and the infrared detector

Answer 12

to make the measurements repeatable

Question 13

what can we use if we dint have an infrared detector

Answer 13

a thermometer with the bulb painted black, but the resolution of the thermometer is less than the infrared detector

Question 14

what is resolution

Answer 14

the smallest change that can be detected

Question 15

how to measure the absorbency of infrared by different surfaces

Answer 15

1. Place an infrared heater in between two metal plates
   - one plate has been painted with shiny metallic paint whilst the other has been painted with matt black paint
   - on the other sides of the plate, we have used vaseline to attach a drawing pin
2. Switch on the heater and start timing
3. Results should show that the temperature of the metal plates increases as they absorb infrared
4. We record the time it takes for the vaseline to melt and the drawing pins to fall off
   - what we find is that the drawing pin falls off the matt black plate first, this is because matt black surfaces absorb more infrared than shiny metallic surfaces

Question 16

why do we use a datalogger in the waves practical

Answer 16

because the time between the two measurements is very short