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Volunteering at Scouts is changing to help us reach more young people

Volunteering is changing to help us reach more young people

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Bring it Ohm

Act fast and find the colours of the Ohm-bow in this resistor recognising race.
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You’ll need

  • Scissors
Reading resistors
PDF – 288.4KB
Download Reading resistors

Resistors are tiny electrical components, essential to many electronic circuits. Because they are so small, it would be very difficult to label them with all the information required. Instead they are labelled using a series of coloured bands.

Most resistors have four bands. One end will be a gold or silver band which represents the tolerance of the resistor (gold = 5% and silver = 10%) The tolerance is how accurate the resistor is, meaning that a resistor marked with a silver band has a 10% margin of error to the value that the other bands mark it as.

Take a look at a resistor with the tolerance band on the right. The other three then give the value of the resistor. From left to right:

  • The first band (left-most) represents the first digit of the resistor value.
  • The second band represents the second digit of the resistor value.
  • The third band is the multiplier of this value.

For example for a 47 Ω resistor, the first band will be yellow (4), the second band will be violet (7) and the third band will be black (x1).  (47x1=47)

  • A 470 Ω resistor would be represented by yellow (4), violet (7), brown (x10). (47x10=470)
  • A 4.7 Ω resistor by yellow (4), violet (7), gold (x0.1) (47x0.1=4.7)
  • If anyone is not as confident in their maths skills, have a calculator to hand to help check any calculations.

 

Before you begin

  • Prepare some coloured strips to represent each of the colours of resistor band, with enough for a complete set per group. Alternatively used other coloured items such as pencils, cones or even books to represent the band colours. (examples of these colours can be found in the attached reading resistors sheet)

Play the game

  1. Divide the group into small teams
  2. Give each team a copy of the resistor values sheet and a set of coloured stripes to represent the coloured bands on the resistors.
  3. Check that everyone understands how the numbering system works, encourage anyone that does understand to support anyone that might be struggling.
  4. The teams begin at one end of the room and the person leading the activity should stand at the other end.
  5. The person leading the activity will call out a value that a resistor might have, for example 470Ω (ohms).
  6. The teams should then decide what order and what colour strips the resistor would have.

For example 470Ω would be: yellow (4), violet (7), brown (x10). (47x10=470)

  1. Three members of the team take a strip each and make their way to the person leading the activity as quick as they can, they should stand in the correct order, left to right.
  2. Teams get a point for each correct combination and an additional point for being the first team to present their correct combination to the person leading the activity.
  3. Keep playing until you feel that the system is clear and everyone has had a go.

Comparing components

  1. Come together as a group again. Let’s look at some other components. Resistors are marked with coloured strips, but other components use different systems. Many simply carry numbers, have you ever looked at a:
    • Capacitors are marked with a number of different letters and numbers to give their capacitance (how much charge the capacitor can store) this is measured in farads and microfarads. If there is room they also put the voltage rating on. Capacitors can look like a bit of a mess and letters and numbers will vary with their size and manufacturer, make sure you check them carefully before using.
    • Bulbs carry lots of numbers and ratings, including how many V(volts) they can take and how many W(watts) they are.
    • Integrated circuits have a notch and a dot mark. This is to help you count the pins which start with number 1 at the dot and count anti-clockwise around the chip.
    • Diodes are marked with a band on one end, this is to tell you which end is the cathode (negative) The end without the band is called the anode (positive).
  1. As a group, think about why it might be important to know the rating of different components.

One answer is that using the wrong components could result in the components breaking or making the circuit unsafe or unstable. Marking components with numbers, symbols or colours means that they can be read easier than if they were written in words, it also makes them international, you don’t need to be able to read a particular language to understand the colours.

Reflection

This activity needed quick thinking to work out which colours were needed. Lots of things in today’s world are represented by colours or symbols instead of words. Can you think of any? Traffic lights are an example that are the same the world over, whatever country you are in and whatever language you speak, red means stop and green means go. What about bags of crisps? What do the different colours make you think of?

Think about the coloured strip marking system used on resistors, what might happen if you got your maths wrong or were colour-blind? What are the risks of using the wrong resistors? You might damage the components but worse you could get yourself or someone else hurt.

Safety

All activities must be safely managed. You must complete a thorough risk assessment and take appropriate steps to reduce risk. Use the safety checklist to help you plan and risk assess your activity. Always get approval for the activity, and have suitable supervision and an InTouch process.

Scissors

Supervise young people appropriately when they’re using scissors. Store all sharp objects securely, out of the reach of young people.

Active games

The game area should be free of hazards. Explain the rules of the game clearly and have a clear way to communicate that the game must stop when needed. Take a look at our guidance on running active games safely.

Electronics

Remove any equipment you’re working on from the power source before you begin. Never assume the power circuit’s off – test it with a voltmeter (and then test it again to be sure). Only connect power to a circuit once you’ve finished working on it and have checked your work. Make sure your circuit isn’t overloaded, and return any covers you’ve removed.

Make sure that all electronics equipment is properly grounded. Use the right electronics tools, and always replace damaged equipment (for example, replace cables rather than repairing them with insulating tape). Always have safety equipment including a fire extinguisher, basic first aid kit, and mobile phone nearby.

  • Try giving some colours instead of numbers and tasking the group to work backwards and figure out what the value would be.
  • Try to get hold of a few examples of each of the other types of components, try using your codebreaking skills to work out the values and meaning of each one.

Vary the size, number of strips, values of your resistors and the course that your players need to run to meet the needs of your group.

All Scout activities should be inclusive and accessible.

Scouts Electronics Activity Badge

Why not look at how other electrical components are marked with their values. How do they compare to the system used by resistors?

This activity is a great opportunity for those with existing skills or interest in electronics to share their knowledge, encourage young people to pass on their skills to others by helping lead this activity or guiding anyone struggling.