# How to Measure Voltage across Resistor

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. These act to reduce the flow of current and at the same time to lower level of voltage within circuits. Voltage on the other hand is an electromotive force or potential difference expressed in volts and it can be explained as the ratio of two voltages. In order to measure voltage across a resistor, you need to keep in mind the concept of ohm’s law as well as series and parallel arrangement of circuits. In order to **measure voltage across a resistor**, the following tips can be bought into use:-

## How to Measure Voltage across Resistor

**1. Know What Voltage is:-**

Voltage is actually the difference in electric potential energy between two points per unit electrical change. Voltage between two points can be defined as work done per unit of charge against a static electric field to move the test charge between two points. Voltage is obtained in joule per coulomb.

**2. Consider the Ohm’s Law:-**

According to Ohm’s law, “I” or Current is equal to V/R or Voltage divided by Resistance and hence if we know two of these values, we can easily find the other putting those values in the relation (I = V/R). Where value of “V” comes out to be I*R or “Current” multiplied by “Resistance”

**3. The Series Arrangement of Circuit:-**

In series arrangement, each and every device is provided with the same value of input irrespective of its specified needs. Everything is arranged in a row within the same loop of wire and if any of the connected appliances meets a malfunction, the entire arrangement gets affected. The current is also the same at every point in this circuit.

**4. Calculating total Resistance In Series:-**

Suppose if three resistances each of 2 ohm, 3 ohm and 5 ohm are connected in a series arrangement, we will get its total resistance as the sum total of all these resistances i.e. 2+3+5 = 10 ohm. Ohm’s law can then be applied within the same arrangement putting the values of current or voltage in it to find the unknown unit. I.e. if I tell you that voltage within the same arrangement is 12V, we can easily find the current by putting the values in “I=V/R” which will be equal to “I= 12/10= 1.2 Ampere current and in the same way if I tell you that current is 1.2 Ampere, you can find the voltage by putting the value of “R” and “I” in the same relation i.e. “I=V/R” which gives 1.2= V/10 and thus value of voltage comes out to be 12.

**5. The Parallel Arrangement of Circuit:-**

Unlike series arrangement, every electrical component is not arranged within the same loop of wire and instead a wire gets splitted in two or more separate ends after leaving one end of the battery and then run parallel to each other. The wires join up against after reaching the other end and this way the circuit is not affected even if one of the electrical components fixed within this arrangement meets a malfunction or stops functioning. The entire circuit is not affected this way.

**6. Calculating Resistance in Parallel Arrangement of Circuit:-**

Suppose if there are two resistors connected in parallel, i.e. 2 ohm 8 ohm, it will give the total resistance in parallel as 1/2 + 1/8 i.e. 5/8. The total resistance here comes out to be 1/⅝ and thus the value of resistance comes out to be 8/5 i.e. 1.6 ohms. We can follow the same approach of “I”= V/R to find a value of current, *voltage or resistance* if any two values are given in a question with parallel arrangement of circuit taken as a base.