Ohm's Law
What is the formula for voltage, given resistance and current?
V = I x R
What do the first 2 bands on a 4-band resistor represent?
The first two bands represent the first and second digits of the resistor value.
Which prefix is represented by μ?
Micro
In a series circuit, how do resistance combine to find total resistance?
Add up all of the resistor values to get total resistance in the circuit.
In parallel circuits, how do the branch voltages compare to the supply voltage?
Each branch will have the same amount of voltage (the same value as the supply voltage)
A resistor has 10 ohms and the current is 2A. Find the voltage across the resistor.
V = I x R
V = 2A x 10 ohms
V = 20V
What do the 3rd and 4th bands on a 4-band resistor represent?
3rd is the multiplier and 4th is the tolerance.
Convert 3mA to amps.
0.003 A
Two resistors, 5 ohms and 10 ohms, are in series across a 15V battery. What is the total resistance and the current through the circuit?
RT = 15 ohms
I = 1 A
Two resistors, 6 ohms and 3 ohms, are connected in parallel across a 12V source. What is the total resistance of the pair?
1/RT = 1/R1 + 1/ R2
= 1/6 + 1/3
= 1/6 + 2/6 = 3/6
Flip the fraction = 6/3 = 2 ohms
A device draws 0.5A from a 12V supply. What is its resistance?
R = V / I
R = 12V / 0.5A
R = 24 ohms
A 4-band resistor shows bands: yellow, violet, red, gold. What is its resistance and tolerance?
yellow = 4
violet = 7
Red = x100
Gold = +/- 5%
4700 +/- 5%
Rewrite 0.000002A using a more appropriate electronic prefix.
2 μA
How do the voltages across individual resistors relate to the total supply voltage?
The individual voltages across each resistor should add up to the total supply voltage.
Three resistors (40, 36, 100) are in parallel across a 12V source. What is the total current drawn from the supply?
I = V / R
12/40 = 0.3A
12/36 = 0.33A
12/100 = 0.12
IT = 0.3 + 0.33 + 0.12 = 0.75A
Two resistors, 8 ohms and 4 ohms, are in series across 24V. Find the current.
RT = R1 + R2 = 12 ohms
I = VT / RT
I = 24V / 12 ohms
I = 2A
Decode a 4-band resistor with bands: brown, black, black, silver. Give its resistance and tolerance.
Brown = 1
Black = 0
Black = x1
Silver = +/- 10%
10 +/- 10%
A circuit has 47μA. Write its amperage in base units.
0.000047 A
Four resistors in series are 2, 4, 6, and 8 ohms. If the supply is 20V, find the current and the voltage across the 6 ohm resistor.
I = 1 A
Voltage at 6 ohm resistor = 6V
A parallel circuit has 3 branches - I1 = 2A, I2 = 1.5A, and I3 is unknown. If the supply provides 5A total, find I3 using Kirchhoff's Current Law.
IT - I1 - I2 = I3
5A - 2A - 1.5A = 1.5A
I3 = 1.5A
A resistor dissipates 6W when connected to 12V. Find its resistance.
R = V2 / P
R = 122 V / 6W
R = 24 ohms
A 4-band resistor reads: orange, orange, brown, gold. Determine its resistance and tolerance.
Orange = 3
Orange = 3
Brown = x10
Gold = +/- 5%
330 +/- 5%
Convert 2 megaohms to milliohms.
2,000,000,000 milliohms
A series circuit has two unknown resistors, R1 and R2. The supply is 24V and the current is 2A. If R1 is twice R2, find both resistances.
RT = VT / IT = 24V / 2A = 12 ohms
R1 = 8 ohms
R2 = 4 ohms
Two resistors, R1 and R2, are connected in parallel across a 24V source. The total current drawn from the supply is 6A and the current through R1 is twice the current through R2. Find R1 and R2.
6A split 3 ways is 2A. If R1 is twice of R2, then R1 is 4A and R2 is 6A
R = V / I
R1 = 24 / 4A = 6 ohms
R2 = 24V / 2A = 12 ohms