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What do I need to know about validity and how can I understand it?

Validity is a complex issue to understand as it is closely linked with reliability. Ultimately, it can be defined as the extent to which something measures what it is supposed to. In simple terms, this means...
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What is homeostasis and why is it important? Give an example of a body condition that must be controlled and how.

In order to remember the definition of homeostasis it is useful to memorise the mnemonic ‘MACIE’; the Maintenance of A Constant Internal Environment. Conditions in the body must be constantly controlled beca...
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Answered by Tierney A. • Biology tutor
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Why can graphite conduct electricity but not diamond?

In graphite, each carbon atom is covalently bonded to three other carbon atoms. One of the four outer shell electrons of each carbon atom is therefore not engaged in bonding, and becomes delocalised. These d...
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Answered by Tierney A. • Chemistry tutor
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A wire has length l, cross-sectional area a, resistivity p and resistance R. It is compressed to a third of its original length but its volume and resistivity are constant. Show its new resistance is R/9.

First realize if its length is now l/3 but its volume is constant its cross sectional area is 3a. Substitute those into the equation for resistance R=p(l/a) and you get (1/9)(p(l/a))= R/9
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Describe how the strong nuclear force between two nucleons varies the distance between the 2 nucleons.

The strong force between two nucleons is initially repulsive. However at a distance of around 1 fm the force crosses over and becomes repulsive. The strong nuclear force is only seen to act over short distan...
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