This thesis looks at the third harmonic voltage response of a small incandescent lightbulb. The third harmonic voltage, or 3 omega (3ω) voltage, arises from applying a 1ω sinusoidal voltage across a resistive material. The 3ω voltage carries with it information about the thermal conductivity of the material. A lock-in-amplifier is used to analyze and measure the 3ω voltage; the abilities of the lock-in amplifier are explored using an RLC series circuit. Our initial findings show the lock-in amplifier is able measure the 3ω signal of a small lightbulb without needing to subtract out the larger first harmonic voltage, the 1ω signal.