Visual Method for remembering formulas for Total Resistance (RT), Total Capacitance (CT), and Total Inductance (LT)
C1
R1
L1
C2
R2
RT = R1 + R2 + R3 …
L2
CT =
1
C1
R1
RT =
1
R1
+
1
1
R1
+
R2
1
R1
…
+
1
1
C1
+
1
C1
C1
LT = L1 + L2 + L3 …
…
C2
L1
C T = C1 + C2 + C 3 …
LT =
1
L1
+
1
1
L1
L2
+
1
L1
…
Other Important Formulas
Ohm’s Law states… “the current flowing through a circuit is directly proportional to the
voltage of the circuit, and inversely proportional to the resistance of the circuit.”
The algebraic expression for Ohm’s Law is… E = I * R
Kirchoff’s Law states… “The algebraic sum of all voltages in a loop must equal zero.”
This can be expressed as VT = VDROP1 + VDROP2 + VDROP3 …
Further Explanation: Let’s say the voltage of a circuit is +30V… if the voltage
drop across the first load is -5V and the voltage drop across the second load is -10V, then
the voltage drop across the third load must equal -15V. Pay attention to the minus sign
on the voltage drops… a drop in voltage is negative while the applied voltage is positive.
Together, the algebraic sum will equal zero.
Power (measured in Watts) = Current (I) * Volts (E); P = I * E
Calculate Total Resistance (RT), Current (I), and voltage drops across resistors
R1
R2
1. If circuit voltage equals 30 volts, R1 equals 20 Ω, and R2 equals 40 Ω, what is the
total resistance, total current, voltage drop across R1, and voltage drop across R2?
Calculate Total Resistance (RT), Current (I), and voltage drops across resistors
R1
R2
2. If circuit voltage equals 50 volts, R1 equals 700 Ω, and R2 equals 3k Ω, what is
the total resistance, total current, voltage drop across R1, and voltage drop across
R2?
Calculate Voltage of the circuit (E)
R1
R2
3. If R1 equals 25 Ω, R2 equals 450 Ω, and the current equals 0.5 A, what is the
circuit voltage?
Calculate Voltage of the circuit (E), and voltage drop across R2
R1
V
R2
4a. If R1 equals 6k Ω, R2 equals 900 Ω, and the current equals 13.3 A, what is the
circuit voltage?
4b. What will the voltmeter read?
Find the value of a resistor in a circuit
R1
R2
5. If the circuit voltage equals 5 V, total current equals 15A, and R2 equals 10k Ω,
what is the value of R1?
Find the value of a resistor in a circuit, and the voltage drop across a resistor
R1
V
R2
6a. If the circuit voltage equals 14 V, total current equals .75 A, and R1 equals 21 Ω,
what is the value of R2?
6b. What will the voltmeter read?
Determine the voltage drop across a resistor
V
R1
R2
R3
7. If the circuit voltage equals 20 V, total current equals 5 A, R1 equals 100 Ω, and
R2 equals 300 Ω, what will the voltmeter read?
Calculate Total Resistance (RT), and Current (I)
R1
R2
R3
8a. If the circuit voltage equals 50 V, R1 equals 100 Ω, R2 equals 300 Ω, and R3
equals 500 Ω, what is the total resistance?
8b. What is the current?
Calculate Total Resistance (RT), and Current (I)
R1
R2
R3
9a. If the circuit voltage equals 115 V, R1 equals 5k Ω, R2 equals 10k Ω, and R3
equals 30k Ω, what is the total resistance?
9b. What is the current?
Find the power of a circuit
R1
R2
10. If the circuit voltage equals 5 V, R1 equals 10 ohms, and R2 equals 30 ohms,
how many watts of power is produced?
Find the power of a circuit
R1
R2
11. If the circuit voltage equals 50 V, R1 equals 5 ohms, and R2 equals 10 ohms,
how many watts of power is produced?
Power vs. Amps
12. If a circuit has a current of .5 amps, and a circuit voltage of 14 volts, what is the
power of the circuit?
13. If a circuit has a voltage of 28 volts and a current of 3 amps, what is the power
of the circuit?
14, If transceiver has a power rating of 70 watts, what will be the current draw
when used in a 28 volt aircraft?
15. What will the current be when the same transceiver is used in a 14 volt
aircraft?
Calculating Battery Capacity
16. If a battery produces 5 amp-hours of energy, how long can the battery operate
a 1 amp load?
17. If a battery produces 2.5 amp hours of energy, how long can the battery
operate a 1 amp load?
18. How much load can a 5 amp-hour battery supply power for 1 hour?
19. If a circuit with a 3 amp load needs to operate on battery power for 30 minutes,
what amp-hour rating must the battery have?
Resistor Color Codes
20. If a resistor has color bands of Blue, Gray, and Orange, what is the value of the
resistor?
21. If a resistor has color bands of Brown, Green, Yellow, and Silver, what is the
value of the resistor?
22. If a resistor has color bands of Red, Violet, Black, and Gold, what is the value of
the resistor and what is the tolerance?
23. If a resistor has color bands of Black, Yellow, and Brown, what is the value of
the resistor and what is the tolerance? What is the range of acceptable values
when measured?
24. If a resistor has color bands of White, Blue, and Black, what is the value of the
resistor and what is the tolerance? What is the range of acceptable values when
measured?