Activity for students aged 11-16 that takes about 60 minutes of class time
Subjects: Science, Engineering, Design & Technology
Key words: resistance; sound; electric circuits; conduction; vibrations; microphones; sound transmission; design
In this activity students get a chance to see the historic demonstration of Alexander Graham Bell’s liquid transmitter and discuss how the setup works, reviewing their knowledge of resistance. Students then get to build a working microphone from pencil leads and consider how to improve their microphone design.
Projector or interactive white board
‘lead’ from pencils
match box or small boxes
Challenge students to identify the biggest differences between modern smartphones and the first telephones.
Watch video of Alexander Graham Bell’s liquid transmitter from the Christmas Lectures.
Use the worksheet to label the elements used in the demo and give a one or two sentence explanation of what they are for (10 mins)
Discuss the idea of resistance in a circuit and how resistance varies with length. (5 mins)
Explain will now have a go building own model of a microphone
Go through PowerPoint slides and in pairs or small groups students have a go building a microphone (15 mins)
Students demonstrate their microphones and as decide which microphone is working best and why. (10 mins)
Students work together in their group to create an explanation of how they think that this microphone works. (10mins)
Ask students to outline the potential disadvantages to this design of microphone and to Alexander Graham Bell’s liquid transmitter (5 mins)
Removing the graphite from inside pencils can be difficult. If you find this too difficult you can be useful to use refills for mechanical pencils.
It can be interesting to put the design of Alexander Graham Bell’s (AGB’s) liquid crystal transmitter in perspective.
Discussion and explanation of resistance can be varied according to the ability of the group and their previous knowledge.
Reiterate that the pin in the AGB model is dipping in and out of the liquid thus more or less of the pin is in contact with the acid at any particular time - which in turn increases and decreases the resistance.
Let students explore and develop optimal methods for constructing their microphones.
Allow students time to explore and test their creations and also to see how other groups microphones compare to theirs
Discussion of how microphones work can be led to a greater or lesser extent by the teacher. Draw the students attention to the materials involved in the construction, how the materials are arranged and where the battery and earphones are connected. What element of the construction is varying or changeable with the sound or vibrations from your voice.
When considering disadvantages of each microphone designs draw students’ attention to the idea of the sensitivity of the materials and their responsiveness to vibration. Reiterate why the membrane was used.
Depending on time the final aspect of the lesson could be completed as homework.
Students are given an image of the liquid transmitter and work in pairs to explain the function of each part of the equipment.
If students are struggling can be useful to give them the worksheet first and let them identify the parts while watching the video. Figuring out function of each part can be completed as a group discussion.
Challenge students to sketch a diagram of their pencil microphone and to write a short paragraph describing how it works.
Supported by the Institution of Engineering & Technology
View the full CHRISTMAS LECTURES, Sparks will fly: How to hack your home, along with behind the scenes footage and related content on the Ri Channel richannel.org/christmas-lectures