Download Equations and Key Concepts (Excellence Project)

IT 318
Aaron Sayre
Excellence Project Winter 2010
Electrical/IT Laws
Ohm’s Law
I=Current (in amperes A)
E=Voltage (in volts V)
R=Resistance (in Ohms Ω)
𝐸
𝐼=
𝑜𝑟
𝑅
Power
P=Power (in watts w)
𝑃 = 𝐼𝐸
𝑜𝑟
𝐸 = 𝐼𝑅
𝑃 = 𝐼2 𝑅
𝑜𝑟
𝑜𝑟
𝑅=
𝐸
𝐼
𝑃=
𝐸2
𝑅
Shannon’s Law
𝑆𝑖𝑔𝑛𝑎𝑙 𝒘 𝑜𝑟 𝒗
)
𝑁𝑜𝑖𝑠𝑒 𝒘 𝑜𝑟 𝒗
log 𝐴
Remember that log 2 𝐴 =
log 2
𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 = (𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ 𝑯𝒛) log 2 (1 +
Key Terms and Concepts
Voltage is the potential or difference. It is the energy or pressure in a circuit. In S.I. units it is 1
joule/coulomb. (See p. 4).
Current is the flow of electrons in a circuit. It is measured in amperes. 1 ampere = 6.24 x 1018/sec.
Resistance is the tendency of a material to resist the flow of electrons. It is measured in Ohms (Ω).
Conductance is the inverse of resistance. It is the tendency in a material to conduct the flow of electrons.
Series Circuit: when batteries are applied in series the voltages are added; the ampacity equals the lowest
ampacity in the circuit. When resistors are added in series, the total resistance is simply the sum of
the individual resistances:
𝑅𝑇𝑜𝑡𝑎𝑙 = 𝑅1 + 𝑅2 + 𝑅𝑛
and the voltage drops are added:
𝐸𝑇𝑜𝑡𝑎𝑙 = 𝑉𝑅1 + 𝑉𝑅2 + 𝑉𝑅𝑛
Parallel Circuit: When batteries are applied in parallel the voltage equals the lowest voltage in the circuit;
the ampacities are added. When resistors are added in parallel the total resistance is calculated using
the following formula:
1
𝑅𝑇𝑜𝑡𝑎𝑙 =
1
1
1
+
+
𝑅1
𝑅2
𝑅𝑛
Reactance opposes change in voltage and current in a circuit and causes phase change:
XL opposes change in current (I)
𝑿𝑳 = 𝟐𝝅𝒇𝐿 (𝒇 𝑖𝑛 𝑯𝒛 𝑎𝑛𝑑 𝑳 in Henries H)
XC opposes change in voltage (E)
𝑿𝑪 =
𝟏
𝟐𝝅𝒇𝑪
((𝒇 𝑖𝑛 𝑯𝒛 𝑎𝑛𝑑 𝑪 in Farads F)