Self Assessment

Answer these questions then check your answers against those given.

1. The picture shows a simple musical instrument made by a child. The child wants to make louder sounds with it. What advice would you give in order to achieve this?

Fig 6. Simple bowed instrument

2. This is a picture of a simple version of an African finger piano or kalimba. Each of the keys 1 - 5 can be plucked with a finger to give a sound.

 

Fig 7

Which keys would you pluck to play the first three notes of Three Blind Mice? or the three opening notes of the Beatles' song All You Need is Love? (It begins: "Love, Love, Love".)

3. (i) A referee's whistle is blown loudly. Draw the pattern you would expect to see on an oscilloscope screen.

(ii) An opera singer sings a low quiet note. Draw the pattern you would expect to see on an oscilloscope screen.

4. A teacher asked a child to draw how a musical instrument can be heard from outside the classroom. This was the drawing produced.

List the child's possible misconceptions (alternative frameworks) regarding sound.

List the ideas that the child does correctly understand about sound.

Fig 8 Child's drawing

Answers

The following are some examples of the answers you might give. There may be others just as valid.

 

1. (a) The child could be encouraged to pluck the string more forcibly, thus giving it more energy.

(b) The child might fix a hollow sound box (plastic ice cream container for instance) to the cane or connect one end of the string to the hollow box. Some amplification would be achieved if the string were merely plucked directly over a hole in the box.

(c) The child might be able to use a microphone and electrical amplifier to increase the sound output.

2. The three note are descending in pitch so any of the following would be fine.

5, 4, 3 5, 4, 2 5, 4, 1 5, 3, 2 5, 3, 1 5, 2, 1

4, 3, 2 4, 3, 1 4, 2, 1

3, 2, 1

3. Fig 9

(i) Referee's whistle (ii) Opera singer's low, quiet note

 

(i) indicates a high pitch (many vibrations per second) and high amplitude (loudness)

(ii) indicates fewer vibrations per second (low pitch) and a quiet note (low amplitude)

4. Alternative conceptions

The child is confusing cause and effect by suggesting that the sound makes the vibrations.

The child may believe that sound will not travel through solids such as the door. The child knows, however, that the sound will be heard faintly and has explained this by suggesting that the sound travels through the gap under the door.

The child appears to believe that sound travels by the movement of the air as though an air current is necessary.

The child shows no sign of understanding that sound can be reflected.

The child would need to be questioned as to whether the sound from the drum moves in all directions.

It is not clear from the drawing that the child understands what a vibration is.

There is a suggestion that the ear is involved but this is not absolutely clear from the drawing

Correct ideas

The child appears to understand that some form of energy is needed to produce a sound. (The beating of the drum.)

The child knows that sound travels from the source to the observer (shown by the arrows).

The child has some knowledge that an obstacle like a door will reduce the volume of sound heard on the other side

Contents

What is sound, Vibration
Sounds travel
The speed of sound in air, Sound travels in solids and liquids too, Hearing sounds through solids
Receiving vibrations at the ear drum, Amplitude of vibrations and loudness
Frequency of vibrations and pitch
Amplification of sounds