Question

Fig. 3.1 shows apparatus called a ripple tank.
This is used to investigate water waves.
An electric motor causes the board to vibrate.
At a constant speed of rotation, the motor produces waves at a constant rate.

(a) The electric motor causes the vibrating board to move up and down at a known frequency.
      This produces water waves with the same frequency.
       (i) State the meaning of the term frequency.

      (ii) The ripple tank produces waves with a frequency of 5.0Hz which travel at a speed of 0.20m/s.
             Calculate the wavelength of the water waves.

              wavelength = ……………………… m

      (iii) Describe how the diffraction of water waves is demonstrated using a ripple tank.
             Include a description of what is observed.
             You may draw a diagram to help with your answer.

(b) The ripple tank uses a simple d.c. motor.
      Complete the sentences to explain how the motor rotates.
      The current‑carrying coil experiences a force because it is in a …………………………………. field.
      The force on one side of the coil is upwards and the force on the other side of the coil is …………………………………., causing a turning effect.

(c) The ripple tank uses a filament lamp during the demonstration.
      (i) Draw the circuit symbol for a filament lamp.

      (ii) The potential difference across the filament lamp is 12V.
            During the demonstration, the filament lamp uses 24000J of electrical energy.
            Calculate how much charge passes through the filament lamp during the demonstration.
            State the unit of your answer.
            charge = …………………………. unit ……………..