Subelement A: — Topic :
Question 6A27
Element 6 (Radiotelegraph)The formula for determining the power in a DC circuit when the voltage and resistance are known is:
Explanation
In DC circuits, power (P) is fundamentally defined as the product of voltage (E) and current (I): P = EI. However, the question specifies that voltage (E) and resistance (R) are known, not current (I).
To find the power using E and R, we use Ohm's Law, which states E = IR. From Ohm's Law, we can express current as I = E/R.
Substituting this expression for I into the fundamental power formula (P = EI):
P = E * (E/R)
P = E²/R
Therefore, P = (E squared) R is the correct formula when voltage and resistance are known.
Option B (P = EI) and C (P = I²R) are also valid power formulas, but they require knowing the current (I), which is not given in the problem statement. Option D is not a standard formula for DC power calculation.