Bredhurst Receiving and Transmitting Society

Advanced Radio Amateur Examination

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Power in DC circuits  using the Casio fx-83MS unless otherwise stated

The maths in this topic is in relation to :-

P = V x I, V = I x R, P = V2 / R, P = I2 x R

Here we have simple multiplication and division and also raising to the power of two or squaring the number. The course will show you each item. The button to be pressed will be shown but when numerals need to be entered they will be shown as figures the screen result will be shown at the end of in stages depending upon the calculation.

P = V x I

What is the power in watts with 10000V and 5 amps

10000 5

V = I x R

What is the voltage in V if 5 amps passes through a resistance of 18000

5 18000

Convert 90000V to kV

From the above stage press result 90kV

P = V2 / R

Find the power in watts with 125V and resistance 150

using the fx-83GT PLUS calculator

For this calculation we need to introduce another key   try the following :-     5        result 25.

So back to the question in hand :- Find the power in watts with 125V and resistance 150

  125      150    

From the above stage press note the10 0

so the answer is indicating full value 104.1666667 W

but in the exam the figures would be near a whole number !!!

P = I2 x R

Find the power in kilo watts with 12.5 Amps and resistance 150

  12      5       150   

Note :-that the conversion to the "engineering" value has to be done after the main calculation. The 03 indicates the kilo value 103 : Result 23.4375 kW

kilo 103

Mega 106

Giga 109

So that completes the calculations for this set.

There are more functions to show you but it is hoped that you have taken all the above onboard and it is time to give yourself a coffee / tea break !!!

Next Circuit theory

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