This diagram shows a loudspeaker producing a sound and a microphone connected to a cathode-ray oscilloscope (CRO).

(a) Sound is described as a longitudinal wave. Describe sound waves in terms of the movements of the air particles.

This diagram shows a loudspeaker producing a sound and a microphone connected to a cathode-ray oscilloscope (CRO).

(b) The time-base on the oscilloscope is set at $5 \mathrm{ms}$ ${\mathrm{div}}^{-1}$. Calculate the frequency of the CRO trace.

This diagram shows a loudspeaker producing a sound and a microphone connected to a cathode-ray oscilloscope (CRO).

(c) The wavelength of the sound is found to be $1.98 \mathrm{m}$. Calculate the speed of sound.

The Doppler effect can be used to measure the speed of blood. Ultrasound, which is sound of high frequency, is passed from a transmitter into the body, where it reflects off particles in the blood. The shift in frequency is measured by a stationary detector, placed outside the body and close to the transmitter. In one patient, particles in the blood are moving at a speed of $30 \mathrm{cm}{ \mathrm{s}}^{-1}$ in a direction directly away from the transmitter. The speed of ultrasound in the body is $1500 \mathrm{cm}{ \mathrm{s}}^{-1}$.

This situation is partly modelled by considering the particles to be emitting sound of frequency $4.000\mathrm{MHz}$ as they move away from the detector. This sound passes to the detector outside the body and the frequency measured by the detector is not $4.000\mathrm{MHz}$.

State whether the frequency received by the stationary detector is higher or lower than the frequency emitted by the moving particles.

The Doppler effect can be used to measure the speed of blood. Ultrasound, which is sound of high frequency, is passed from a transmitter into the body, where it reflects off particles in the blood. The shift in frequency is measured by a stationary detector, placed outside the body and close to the transmitter. In one patient, particles in the blood are moving at a speed of $30 \mathrm{cm}{ \mathrm{s}}^{-1}$ in a direction directly away from the transmitter. The speed of ultrasound in the body is $1500 \mathrm{cm}{ \mathrm{s}}^{-1}$.

This situation is partly modelled by considering the particles to be emitting sound of frequency $4.000\mathrm{MHz}$ as they move away from the detector. This sound passes to the detector outside the body and the frequency measured by the detector is not $4.000\mathrm{MHz}$.

Explain your answer.

The Doppler effect can be used to measure the speed of blood. Ultrasound, which is sound of high frequency, is passed from a transmitter into the body, where it reflects off particles in the blood. The shift in frequency is measured by a stationary detector, placed outside the body and close to the transmitter. In one patient, particles in the blood are moving at a speed of $30 \mathrm{cm}{ \mathrm{s}}^{-1}$ in a direction directly away from the transmitter. The speed of ultrasound in the body is $1500 \mathrm{cm}{ \mathrm{s}}^{-1}$.

This situation is partly modelled by considering the particles to be emitting sound of frequency $4.000\mathrm{MHz}$ as they move away from the detector. This sound passes to the detector outside the body and the frequency measured by the detector is not $4.000\mathrm{MHz}$.

(b) Calculate the difference between the frequency emitted by the moving particles and the frequency measured by the detector.

The Doppler effect can be used to measure the speed of blood. Ultrasound, which is sound of high frequency, is passed from a transmitter into the body, where it reflects off particles in the blood. The shift in frequency is measured by a stationary detector, placed outside the body and close to the transmitter. In one patient, particles in the blood are moving at a speed of $30 \mathrm{cm}{ \mathrm{s}}^{-1}$ in a direction directly away from the transmitter. The speed of ultrasound in the body is $1500 \mathrm{cm}{ \mathrm{s}}^{-1}$.

This situation is partly modelled by considering the particles to be emitting sound of frequency $4.000\mathrm{MHz}$ as they move away from the detector. This sound passes to the detector outside the body and the frequency measured by the detector is not $4.000\mathrm{MHz}$.

(c) Suggest why there is also a frequency difference between the sound received by the particles and the sound emitted by the transmitter.

(a) State what is meant by plane polarised light.

(b) Reflected light from the surface of water is partially plane polarised. Describe briefly how you could demonstrate this.