Calculating Simple Resistance

Practice problems for single resistor circuits.

Sample Circuit

Given the following circuit:

Which includes:

  • Source Voltage - A charged battery.
  • Resistor - A simple resistor.
  • Voltmeter - An instrument for measuring voltage.
  • Ammeter - An instrument for measuring amperage.

Let’s calculate the circuit, in a variety of configurations.

Simple Resistance Sample Problems

1) Let’s say we have a 1.5V battery, and the potentiometer set to 10ohms, how many amps will we have?

Given:
I = V/R

Therefore:
I = 1.5V/10Ω = 0.15A = 150mA

1a) How much total power (wattage) would there be?

Given:
W = V*A

Therefore:
Power = 1.5V * 0.15A = 0.225W = 225mW

2) 12V battery, and 1KΩ resistance?

I = 12V / 1,000Ω = 0.012A = 12mA

1a) Total power?

Power = 12V * 0.012A = .144W = 144mW

3) Now let’s say that we have a 1.5v battery, and ammeter reads 15mA, how many ohms is the potentiometer set to?

Given: 
R = V/I

Therefore:
R = 1.5/0.015A = 100Ω

4) What if we need to push 100mA through a 10Ω resistor, how much voltage would the battery need to have?

Given:
V = I * R

Therefore:
V = 0.100A * 10Ω = 1V

Next - Resistor Power Rating


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