In a simple electrical circuit the current in a resistor is measured as (2.50 +_ 0.05) mA. The resistor is marked as having a value of 4.7 _+2%. If these value where used to calculate the power dissipated in the percentage uncertainty in the value obtained ?
Correct answer: C. 6%
- A. 2%
- B. 4%
- C. 6%
- D. 8%
Explanation
First we find out the % uncertainty in current (0.05)/2.5 x 100 = 2%. Then we note the formula of power dissipated is 12 x R so the = percentage uncertainty has to be added i.e (2+2)+2=6%As it is numerical, it can have only one possible answer.
This question appeared on the ETEA MDCAT 2017 paper, which you can sit online with every answer explained.
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About Errors and Significant Figures
Measurement errors include random and systematic effects, absolute, fractional and percentage uncertainty, and the precision shown by significant figures. Questions apply rounding rules and uncertainty propagation in addition, subtraction, multiplication and division, while distinguishing accuracy from precision and uncertainty from an actual mistake.
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