Measurements

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1.general physics  1.1 length and time  -i-Physical Quantity Physical Quantities A physical quantity is a property of an object that can be measured with a measuring instrument. A physical quantity is usually expressed as “a magnitude ( numerical value)  and a  physical unit or more ” Example :- Normal body temperature of a healthy human being is  37  0 C -ii-Length Measuring Length. Length is “the distance between two points in a space”. According to SI units, the length quantity is expressed in meter. There are several kinds of measuring devices used to measure quantity of length, among others, are as follows. Tools used… a-   Measuring tape. b-   Ruler c-   Vernier callipers. d-    Micrometer Measurement of length Length is measured accurately through many meth...
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Electromagnetic effects

electromagnetic induction 

An induced EMF can be made in several ways:
1. If a wire is passed across a magnetic field, a small EMF is induced, this is electromagnetic induction. If the wire forms part of a complete circuit, the EMF makes a current flow. This can be detected using a galvanometer. The EMF induced in a conductor is proportional to the rate at which the magnetic field lines are cut by the conductor.
The induced EMF can be increased by:
-moving the wire faster
-using a stronger magnet
-increasing the length of wire in the magnetic field – for example, looping the wire through the field several
times.
The current and EMF direction can be reversed by:
-moving the wire in the opposite direction
-turning the magnet round so that the field direction is reversed 
The current direction is given by Fleming’s right-hand rule:
A bar magnet is pushed into a coil. If the coil is part of a circuit, a current will flow; 


The induced EMF (and current) can be increased by: -moving the magnet faster
-using a stronger magnet
-increasing the number of turns in the coil
-If the magnet is pulled away, the direction of the induced EMF (and current) is reversed
-using the S pole instead of the N pole reverses the direction of the induced EMF (and current)
-if the magnet is held still, there is no EMF
An induced current always flows in a direction such that it opposes the change which produced it. When a magnet is moved towards a coil the pole of the coil and magnet next to each other are the same. When the magnet is moved away the poles are opposite (opposite poles attract). The pole-type (north or south) is controlled by the direction in which the current is induced. The direction of the current is given by the right-hand grip rule:
The fingers point in the conventional current direction and the thumb gives the North Pole. 

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