Final answer:
Applying Ohm's Law in a simple circuit with only a 30-ohm resistor and a 5V voltage source, the voltage across the resistor is the full 5 volts since there are no other components to drop voltage across.
Step-by-step explanation:
To find the voltage (vr) across the 30-ohm resistor (Ω) using a 5V voltage source, we can apply Ohm's Law, which states that the voltage (V) across a resistor can be found by multiplying the current (I) through the resistor by its resistance (R), expressed as V = IR.
Assuming that the only resistance in the circuit is the 30-ohm resistor and that this is a simple series circuit with no other resistors or components, the entire voltage drop from the source will occur across the 30-ohm resistor. Therefore, the voltage across the resistor will be equal to the source voltage, which is 5V.
This is because, in a series circuit, the total voltage drop across all the components sums up to equal the source voltage according to the principle of conservation of energy. Thus, since there are no other components to drop voltage across in this simplified scenario, the voltage drop across the single 30-ohm resistor is the full 5 volts from the voltage source.