electricity Flashcards
charge symbol and units
Q, measured in coulombs
current symbol and units
I, amps
time symbol and units
t (lowercase), seconds for charge and current relationship
define current
the electric charge transferred per unit time
it is the rate of flow of electrons/charges
Direct Current Definition and suppliers
the flow of charges round a circuit is in a single direction.
Cells, batteries and d.c. power supplies provide this type of current.
alternating current supply (give voltage and frequency) and definition
-mains electricity,
In the UK and Europe this is with a frequency of 50 Hz, 230V
This current reverses direction many times per second, and is not constant
ways to determine ac vs dc
-what source is it from
-using an oscilloscope trace/oscilloscope
explain conventional current
In physics the concept of current is still based on the movement of positive charge, and is called conventional current.
scientists thought that electric current was the movement of positive charges.
With the discovery of the electron and atomic structure we now know that current occurs because of the movement of electrons.
When you see a current arrow on a diagram that refers to conventional current you will see that it goes from the positive terminal of the power supply to the negative one. The arrows for conventional current point in the opposite direction to the movement of the electrons.
what is a field
a region of space where non contact forces can be detected
what path does an electron follow between two oppositely charged parallel plates
it follows the field line to the oppositely charged plate
what is potential difference
ameasure of the energy given to the charges in a circiut
what happens to resistance as temperature goes up? explain
When the wire is heated the particles in the wire vibrate more. These increased vibrations cause the electron to be bounced about more. This makes it more difficult for the electron to pass through the wire. Therefore the resistance of the wire increases when it is heated.
