# Solutions to the Quiz on Waves

Question 1: Which one of the following waves is a longitudinal wave?
• Water waves
• Sound waves
• Electromagnetic waves
• None of the above.

Question 2: What is the period of an ultrasound in a tissue in which the speed of sound is 1600 m/s
and the wavelength of the scanner is 4× 10− 4 m.
• 2.5 10− 7 s
• 2.5 10− 6 s
• 3.5 10− 7 s
• 2.5 10− 8 s
Explanation: wave speed = frequency × wavelegth ⇒ v = f × λ and then f = v / λ = 1600 m/s / 4× 10− 4 = 4× 106 Hz
Period T = 1 / f = 1 / (4× 106 Hz) = 2.5 10− 7 s.

Question 3: If the speed of a wave remains constant, what happens to the frequency when the wave length is halved?

• Doubled
• Halved
• Same
• Zero

Explanation: wave speed = frequency × wavelegth ⇒ f = v / λ

Question 4: Based on the wave below having a frequency of 50 Hz, find its speed. • 200 m/s
• 300 m/s
• 350 m/s
• 400 m/s

Explanation: wave speed = frequency × wavelegth = 50 Hz × 6 m = 300 m/s.

Question 5: The vibrations in a transvers wave move in a direction ________________ to the wave motion.
• parallel
• perpendicular
• opposite
• upward
• downward