RP8 Waves

Question 1

(ripple tank) what is a ripple tank?

Answer 1

a shallow glass tank with an oscillating paddle/needle to create waves. it is illuminated from above so the waves can be seen on the surface below the tank.

Question 2

(ripple tank) outline the basic steps of the practical.

Answer 2

1. set up the ripple tank with a lamp above it and white card/paper below it
2. switch on the motor attached to the wooden rod
3. measure the wavelength of the waves being cast onto the card
4. count the number of waves passing a point in 10 seconds and calculate the frequency
5. calculate the wave speed

Question 3

(ripple tank) approximately how much water should you put into the ripple tank? what would the consequence of too much be?

Answer 3

the water should be poured to a depth of around 5 mm. if there is too much water the rod won’t produce clear waves and they will be less clearly projected onto the card below.

Question 3

(ripple tank) how should the wooden rod be set up in the ripple tank?

Answer 3

the wooden rod should be placed into the tank so that it just touches the surface of the water.

Question 4

(ripple tank) what units should your measured wavelength be in?

Answer 4

metres, m.
(it may be easier to measure in cm, but wavelength must be in m for the wave equation).

Question 4

(ripple tank) how should you measure the wavelengths of the waves on the card?

Answer 4

1. adjust the lamp position so that the waves are clearly projected onto the card
2. using a metre rule, measure across as many waves as you can
3. divide the distance by the number of waves measured across

Question 5

(ripple tank) what equation is used to calculate wave speed?

Answer 5

wave speed = frequency x wavelength

Question 5

(ripple tank) why should you measure across more than one wave?

Answer 5

to reduce the uncertainty in the measurement and improve the accuracy of the value.

Question 5

(ripple tank) how do you measure the frequency of the waves on the card?

Answer 5

1. count the number of waves passing on chosen point in 10 seconds
2. divide the number by 10, to produce a frquency in Hz

Question 6

(solid) outline the basic steps of the practical.

Answer 6

1. attach a piece of string to a vibration generator at one end and to a mass hanger suspended over a pulley at the other
2. place the wooden bridge under the string before it reaches the pulley
3. start the generator and alter the tension and bridge until it looks like the wave isn’t moving
4. measure the wavelength, and record the frequency
5. calculate wave speed

Question 7

(ripple tank) when the frequency is in hertz and the wavelength is in metres, what is the unit for wave speed?

Answer 7

m/s
metres per second

Question 8

(solid) how do you measure the wavelength?

Answer 8

1. using a metre ruler, measure across as many loops as you can
2. each loop is a half wavelength
3. divide the distance by the number of loops and multiply by two to get the wavelength

Question 9

(solid) what value is uised for the frequency?

Answer 9

the value should be taken from the frequency generator settings.