These are similar to one and two mark questions but you will be expected to write in more depth for three and four mark questions.
The answers here give lists of valid points that could be included in your answer.
This page contains AQA material which is reproduced by permission of AQA.
The signals for a baby monitor unit are transmitted as electromagnetic waves with a wavelength of 0.125 m.
Wave speed of electromagnetic waves = 3 × 108 m/s
Calculate the frequency of the signal. [3 marks]
Wave speed = frequency × wavelength
3 × 108 = frequency × 0.125 
frequency = 3 × 108 ÷ 0.125 
= 2.4 × 109 Hz 
The waves generated on the surface of the water are transverse waves.
Describe the differences between longitudinal waves and transverse waves.
You may include labelled diagrams to help your answer. [3 marks]
In longitudinal waves, the particles oscillate parallel to the direction of energy transfer, causing areas of compression and rarefaction. In transverse waves, the particles oscillate perpendicular to the direction of energy transfer, causing peaks and troughs. 
A monitor for a baby sleeping in a cot has a sensor unit that transmits an image of the baby and the noises the baby makes to a monitor unit.
The monitor unit then displays an image of the baby and emits the noises the baby makes.
Compare the properties of the waves that transmit images and noises from the monitor unit. [4 marks]
Answers may include any four points from: