Creating curious circuits

Type: Main
Time: 2 x 60mins
Subjects: Science, Design & Technology, Engineering
Key words: circuits; voltage; resistance; current; LEDs; conductive dough; materials; electricity

Overview
Squishy circuits are an interesting and surprising way to introduce students to circuit building, resistance and conductivity. In this activity students will explore the concept of resistance and how resistance varies for different materials. They will measure voltage and current using an ammeter and voltmeter and use the formula V=IR to calculate resistance. Finally they will investigate how resistance varies with length and width of the conductor.

Materials
Projector or interactive white board
Batch of conductive dough, batch of resistant dough (recipe here)
Selection of materials to test e.g. wood, metal, material, food
Selection of LEDs, coin batteries, dc motors, crocodile clips
Voltmeter, ammeter

Media Resources
Video clip http://richannel.org/makey-makey
Worksheet 1: table for V=IR
Worksheet 2: Electro Dough models peer review 

Watch video of Makey Makey. (5 mins)

Ask students to give an explanation of what electrical conductivity means.Show students a variety of materials. Ask them to decide which materials they think are conductive. (5 mins)

Get students in pairs and give them 5 mins to design a test for the conductivity of the materials. Each pair explains their suggestion. Ideas are collated on the board and a diagram of how to set up the circuit is decided. (10 mins)

Discuss why some materials are conductive and others are not. (5 mins)

Ask students what they think the resistance of materials might mean. Discuss electrical resistance. (5 mins)

Introduce the idea of the relationship between voltage, resistance and current. V = IR (5 mins)

Students build circuits using their materials. They must measure the voltage and current in the circuit for each of their materials using the ammeter and voltmeter filling this information into worksheet 1. (20 mins)

Students use this information to calculate the resistance of each of the pieces of material. This can be completed for homework.

Get students into small groups and give each group some conductive dough and some insulating dough (Recipe for electro dough), an LED and a battery. Give each group 5 minutes to build a circuit using the materials. (5 mins)

Ask students to explain resistance. (5 mins)

Give each student a set amount of conductive dough (approx 30g) and ask students to create a circuit to measure the resistance of a ball of conductive dough. Ask students to experiment to see how the resistance of their piece of conductive dough varies according to length and width. (20 mins)

Tell students they will now be challenged to create an object using the electro-dough.Go through the criteria of how their sculptures will be judged – see worksheet 2. (5 mins)

Students work in groups to create their sculptures. (20 mins)

Students use worksheet 2 to assess each other’s work. (5 mins)

Makey Makey kits use circuit boards to detect currents through traditionally high resistance materials such as skin. The discussion of resistance can be adjusted depending on students’ previous knowledge and understanding.

Differentiation
This lesson assumes that students already have a basic understanding of how to set up an electrical circuit.
If students are unable to use the formula V=IR light bulbs can be used to show varying resistance across different materials

Extension
Challenge students to wire light bulbs in parallel and in series. Ask students to explain why the brightness of the lights changes for each configuration and to speculate how this may relate to resistance.

UK Science

• Experimental skills and investigations
  2b make predictions using scientific knowledge and understanding
  2c select, plan and carry out the most appropriate types of scientific enquiries to test predictions, including identifying independent, dependent and control variables, where appropriate
  2e make and record observations and measurements using a range of methods for different investigations; and evalutate the reliability of methods and suggest possible improvements 
• Analysis and evaluation
  3a apply mathematical concepts and calculate results
  3c interpret observations and data, including identifying patterns and using observations, measurements and data to draw conclusions
  3d present reasoned explanations, including explaining data in relation to predictions and hypotheses 
• Measurement
  4b use and derive simple equations and carry out appropriate calculations 
• Energy changes and transfers
  24c other processes that involve energy transfer: changing motion, dropping an object, completing an electrical circuit, stretching a spring, metabolism of food, burning fuel
• Current electricity
  35a electric current, measured in amperes, in circuits, series and parallel circuits, currents add where branches meet and current as flow of charge
  35b potential difference, measured in volts, battery and bulb ratings; resistance, measured in ohms, as the ratio of potential difference to current

UK Design & Technology

• Make
  2b select from and use a wider, more complex range of materials, components and ingredients, taking into account their properties
• Evaluate
  3c test, evaluate and refine their ideas and products against a specification, taking into account the views of intended users and other interested groups
• Technical knowledge
  4a understand and use the properties of materials and the performance of structural elements to achieve functioning solutions