Basic Flashcards
What is current?
The rate of electron flow
What is the unit of measurement for current?
Amperes/amps
What is the current of 1 A?
1 A = 6.241*10^18 electrons per second
What is charge?
The concentration number of electrons at a given circuit point
What is the unit of measurement for charge?
Coulombs (C)
What is a conductor?
a substance that lets electric charge flow through it
What is an insulator?
a substance that offers high resistance to current flow
What is the actual direction of electron flow?
a flow of electrons from negative to positive
Are electrons + or - charged?
negative
Are protons + or - charged?
positive
Are neutrals + or - charged?
neutral
What is AC?
alternating current changes direction of the current (basically looks like a sound wave–has a positive and negative phase) so electrons are constantly moving in alternating directions
what is DC?
Direct current implies electron flow in one direction only, achieved by the supply of a constant voltage.
What are resistors used for?
to limit the current in circuits
How do you determine the resistance value and tolerance of a 4-band resistor by looking at it?
band 1 = 1st digit band 2 = 2nd digit band 3 = multiplier (1st + 2nd * 3rd) band 4 = tolerance (± x%)
What is a capacitor?
a device used to store an electric charge, made of one or more pairs of conductors separated by an insulator (dielectric)
What is capacitance?
a measurement of the ability of a capacitor to store charge
How does a capacitor store charge?
when connected to an electric circuit one plate attracts electrons and one repels them, leading to a buildup of positive charge on one plate and an equal negative charge on the other.
What is the formula for calculating resistance in series?
RT = R1 + R2 + R3 + R4 +…
what is the formula for calculating resistance in parallel
1/RT = 1/R1 + 1/R2 + 1/R3 +…
What is the direction of conventional current flow? Where is it used and why?
flows positive to negative Used in books and diagrams they were too lazy to change it
What are the two types of current?
alternating and direct
What does the frequency of AC reflect?
how many times in a second the current changes direction
What is the frequency of DC?
does’t have a frequency because it doesn’t change direction
Ohms law
name examples of conductors
silver
copper
gold
aluminium
zinc
nickel
brass
name examples of semi-conductors
carbon
silicon
germanium
Name examples of insulators
rubber
plastic
ceramics
air
dry paper
pure water
wood
What is resistance? What unit of measurement is used?
opposition to current flow
measured in ohms (Ω)
What is a semi-conductor?
a substance that allows current to flow only under specific conditions
can have very useful properies like…
- allowing current to flow more easily in one direction than the other
- showing variable resistance, sensitivity to light or heat
What type of current do we use in homes and other buildings?
AC
What kind of electricity is used by most of our devices?
DC
Define power.
What is the unit of measurement used?
DEF: the rate of work done over time or the rate of using energy.
measured in watts (W)
Define ‘joule’
DEF:
the SI unit of work or energy, equal to the work done by a force of one newton when it’s point of application moves one meter in the direction of action of the force, equivalent to one 3600th of a watt-hour
How many joules are in 1 Watt?
1 W = 1 joule per second
What determines the amount of charge that can be held by a capacitor?
size of plates, distance between them and the material used for the dielectric
Capacitance is measured in ________.
farads (F)
Formula for calculating total capacitance (series)
1/CT = 1/C + 1/C2 + 1/C3 + …
formula for calculating total capacitance (parallel)
CT = C1 + C2 + C3 + …
formula for charge, capacitance and voltage
formula for determining time constant with capacitors (charging time)
t = R x C
where t = time
