4 Analysing and evaluating reasoning
4.1
OCR AS Critical Thinking
Core
Read the passage and answer the questions that follow.
There are some things that it is unwise to put in your microwave oven at home. A microwave is a
powerful heating device. It uses microwaves, which are made up of a vibrating electric and
magnetic field to line up molecules in the material being heated. The field alternates rapidly,
causing the molecules to vibrate back and forth. They generate friction, and this heats the material.
It works best in liquids because their molecules are more mobile.
Putting the wrongs things in your microwave can be messy, as the following experiments show.
First, an egg was placed in a plastic holder in the centre of a microwave oven. The microwave was
set to full power and switched on. The egg exploded, covering the oven’s walls. Water within the
egg had been heated to over 100°C, creating steam. The gas built up until the shell cracked
spectacularly under pressure. Second, a bar of soap was heated on full power. The soap expanded,
creating a polystyrene-like goo. Soap contains water, fats and trapped air which expand when
heated, sometimes to five times the size of the original bar of soap.
There are some things that can cause injury to you if you put them in your microwave. They may
also damage the microwave. First, a CD was stood against a cardboard box inside the microwave so
it was easy to see what happened when it was heated on full power. It melted into an amorphous*
mess. It’s basically a disc of plastic with a thin metal coating which absorbs microwave energy.
This caused the plastic to melt and partially burn off, releasing noxious smoke. Then a roll of steel
wool was heated at full power. The wool glowed like bonfire embers. The electrical charge
absorbed by the metal concentrated at the wool’s jagged edges. These reached high voltages,
leading to flashes of electrical energy, causing fires.
BBC worldwide and the publishers and editors of Focus magazine can accept no responsibility for
personal injuries or damage to property that may result from experimenting with your microwave
oven.
*Amorphous: shapeless, blobby.
(BBC Focus, October 2007, pp 52–53)
1. Identify the main conclusion of the argument.
2. Identify three reasons given to support the conclusion.
3. What sort of evidence is used in this argument?
© Pearson Education Limited 2008
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