Meteorological Instrument Performance Characteristics

### General Characteristics of Measurements » Law of Propagation of Uncertainty » Example: Ohm’s Law

Let’s consider the example of Ohm’s Law P = I2R, where P is power, I is current, and R equals resistance. The uncertainty uc in the power measurement is given by the following equation:

where

and

gives the uncertainty in the current, u.

A set of measurements produce the following estimate of the Measurands (current and resistance) during a calibration test.

I = 15.000 Amps

R = 1.0500 Ω

Variance(I) = 8.28E-06 A2

Variance(R) = 4.6888E-09 Ω2

Covariance(I, R) = -5.2E-09 A Ω

The uncertainty in the power measurement, P, can be computed based on the following equation:

Use the values above to solve for .

#### Question

The correct value for is: