Final answer:
The voltage drop in a single-phase circuit is defined by Ohm's law with the formula V = IR, indicating that the voltage drop (V) across a resistor is the product of the current (I) flowing through it and the resistance (R) of the resistor.
Step-by-step explanation:
According to Ohm's law, the voltage drop, V, across a resistor when a current flows through it is calculated using the equation V = IR, where I equals the current in amps (A) and R is the resistance in ohms (Ω). This equation can be thought of as the voltage needed to drive a current I through resistance R.
This concept of voltage drop is similar to fluid pressure in pipes, where the voltage is like the pressure created by a pump, and the resistor is like a pipe that reduces pressure due to friction, which in this case is the resistor's opposition to current flow.
The voltage supplied by the source is converted into another form of energy by the resistor, typically thermal energy, which follows the principle of conservation of energy. Therefore, in a simple circuit with one resistor, the voltage supplied by the source equals the voltage drop across the resistor. Power in the circuit can also be expressed in terms of voltage drop, using either P = IV, where V is the voltage across the resistor or P = I2R.