# PH1 physics definitions

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1. Define Newton's third law
If body A exerts a force on body B, then body B exerts an equal and opposite force on A
2. What is the moment about an axis?
Force x perpendicular distance from the axis.
3. What is the principle of moments?
For a system in equilibrium, the resultant moment = 0
4. Define what is meant by the centre of gravity
The point where the entire weight of the body is considered to act.
5. Define Displacement
The displacement of a point B from a point A is the shortest distance from A to B together with the direction
6. Define Energy
The ability to do work
7. State the principle of conservation of energy
Energy cannot be created or destroyed, only transferred from one form to another.
8. Define Drift velocity
The small average speed of electrons in a conductor due to an applied pd.
9. define 'n'
The number of free electrons per cubic metre
10. Define potential difference
• The energy converted from electrical potential energy to some other form per coulomb of charge flowing from one point to another.
• Unit = JC-ยน
11. The resistance of a conductor
The pd placed across it divided by the resulting current through it.
12. Define Ohm's Law
The current flowing though a metal wire is proportional to the pd flowing across it provided temperature is constant.
13. Define EMF
• The e.m.f. of a source is the energy converted from some
• other form (e.g. chemical) to electrical potential energy per coulomb of charge
• flowing through the source.

• Unit:
• V.
14. Define a superconductor
A conductor with zero resistance
15. What is meant by the superconducting transition temperature?
The temperature at which a material when cooled suddenly, loses all its electrical resistance and becomes a superconductor.

## Card Set Information

 Author: keesukim ID: 215291 Filename: PH1 physics definitions Updated: 2013-04-28 10:28:55 Tags: PH1 Folders: Description: definitions shown at PH1 Show Answers:

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