Q1.
Do you remember learning in an earlier chapter, about electric furnaces for melting steel?
Answer
Yes — in Chapter 4, Electricity: Magnetic and Heating Effects. There we learnt that the heating effect of electric current is used in a specially designed high-temperature furnace, an enclosed space built to generate heat, in which scrap steel is melted and recycled into usable steel.
A solar furnace reaches the same very high temperature by a completely different route. Instead of pushing a current through a conductor, a large concave mirror (or a field of mirrors) concentrates sunlight onto a small target.
| Electric furnace | Solar furnace | |
|---|---|---|
| Where the energy comes from | Electric current | Sunlight |
| How heat is produced | Heating effect of current in a conductor | Reflection — sunlight concentrated by mirrors onto a small area |
| Running cost and fuel | Needs a continuous electricity supply | No fuel; works only while the Sun shines |
Why the comparison is worth making: both furnaces do the same job — crowd a lot of energy into a small space. The electric furnace does it by choosing where the current meets resistance; the solar furnace does it by choosing where the light rays meet. The mirror in a solar concentrator is doing on a huge scale exactly what your small concave mirror did to a sheet of paper in Activity 10.7.