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 methods. Here are some: Method Notes Ruler Used to make simple measurements accurate to  0.1 cm  (1 mm) Vernier caliper Used to make simple measurements accurate to
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The magnetic effect of a current

The magnetic effect of a current 

Magnetic field around a current carrying wire and a solenoid:


 1. Increasing the current increases the strength of the field
2. Increasing the number of turns of a coil increases the strength.
3. Reversing the current direction reverses the magnetic field direction (right-hand rule).
•The magnetic effect of current is used in a relay and a circuit breaker. 

 Relay
A device to control the switch of another circuit without any direct electrical contact between them.

1. Magnetic fields that are in the same direction make the combined fields stronger.
2. Magnetic fields that are in opposite direction make the combined fields weaker.
Force on a current carrying wire in magnetic fields

Force on a current-carrying conductor 

If a current carrying conductor is in a magnetic field, it warps the field lines. The field lines from the magnet want to straighten out naturally. This causes a catapult like action on the wire creating a force. The direction of the force, current or magnetic field is given by Fleming’s left-hand rule:


if you reverse the current, you will reverse the direction of the force
-if you reverse the direction of the field, you will reverse the direction of the force. 
Describe an experiment to show the corresponding force on beams of charged particles”
An electron gun creates a beam of electrons. The screen is coated with a fluorescent material which glows when electrons strike it. Current is passed through a pair of coils, to create a magnetic field. NOTE: the direction of the electron beam is the opposite to the conventional current direction so when using the left-hand rule you have to point in the opposite direction of the electron beam.


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