Efficiency ladders

What the Activity is for

Getting a feel for efficiencies.

Here you can impart an idea of the relative values of different efficiencies. Having such an idea for different devices and processes allows the term efficiency to acquire meaning, and enables the values derived from calculations to be checked against an internal model of what is reasonable. The ladders are one-dimensional graphs, used often in the SPT14–16 topics to support quantification, putting any physical quantity into context.

What to Prepare

• appropriate scale prints of the support sheets provided
• prepared values and items to place in order, if these are to be used.
• some Blu-tack
• support sheet (see below)

What Happens During this Activity

The support sheet provides two grids: one with electrical devices to provide some context and one blank. You can use them in a number of ways.

You could provide a blank ladder, of a large scale, on the laboratory wall, and add values to it over the duration of the topic as you encounter these values. It may be helpful to have a number of ladders, one for each class of device: maybe for those switching from the electrical pathway or those switching to the mechanical working pathway, for example. An alternative is to maintain a column for each class of device, as done in the Physics Narrative.

You could provide a completed ladder, adding your own values to it as these come up in the conversations in the class. These could be stimulated by distributing a range of research questions to groups within the class to populate the values.

You could provide a blank ladder to a group, together with a selection of objects and processes, and ask them to agree on how to place these items. Groups might then usefully compare their placements before being given the matching values, and so reordering their values. Or you might provide the unmatched values and objects/processes, only then placing them on the ladder afterwards.

Placing about five items on such a ladder produces a manageable demand.