Resonance (T3)

Question 1

Explain what resonance is and how it comes about…

Answer 1

• if you waggle one end of rope that is fastened at the other end, you can set up a standing wave. This happens because the wave you send down is reflected where the rope is fastened to the wall. If you move your hand at the right frequency the wave and its reflection add together to make a standing wave…
• this also happens when air vibrates inside a tube. The sound wave is reflected and if the tube is the correct length then the reflected wave reinforces the original one.
• this gives a wave with a larger amplitude and this effect is known as RESONANCE

Question 2

How can you use resonance to measure the speed of sound?

Answer 2

• gather a resonance tube and some tuning forks
• a resonance tube is a tube with a water reservoir. The height of the water in the tube can be adjusted to change the length of the tube, as the sound waves will reflect at the waters surface
• strike a tuning fork at a known frequency then hold it above open end of the tube
• the water column is adjusted until the loudest sound can be heard
• the first resonance will be heard when the length of the tube is equal to a quarter of the wavelength
• you can check your result by lowering the water to find the next resonance, at 3/4 of the wavelength
• they speed of sound = frequency (f) x wavelength (λ)