How is resistance calculated

The total resistance R of two or more resistors connected in series is the sum of the individual resistances of the resistors. For the circuit above the total resistance R is given by:. Find the total resistance of the circuit above. This is a series circuit and so total resistance is found using the equation:.

Adding resistors in series always increases the total resistance. The current has to pass through each resistor in turn so adding an additional resistor adds to the resistance already encountered. There are also other possible variations, but these are some of the more common configurations. Resistors are circuit elements that impart electrical resistance. While circuits can be highly complicated, and there are many different ways in which resistors can be arranged in a circuit, resistors in complex circuits can typically be broken down and classified as being connected in series or in parallel.

The total resistance of resistors in parallel is equal to the reciprocal of the sum of the reciprocals of each individual resistor. Refer to the equation below for clarification:. The total resistance of resistors in series is simply the sum of the resistances of each resistor. Where: L is the length of the conductor A is the cross-sectional area of the conductor C is the conductivity of the material.

Temperature Coefficient Color:. However, electricity is not visible. A specialized measuring instrument is necessary in order to investigate whether a circuit has the proper resistance. An instrument such as a tester is necessary in order to measure resistance, but how is such measurement carried out? This page provides a detailed introduction to how a tester or multimeter can be used to measure resistance.

Resistance is measured using an instrument such as an analog multimeter or digital multimeter. Both types of instrument can measure not only resistance, but also current, voltage, and other parameters, so they can be used in a variety of situations. Instead, resistance is calculated by measuring the current and voltage applied to the circuit.

When a current is applied to the circuit under measurement, the circuit resistance exhibits a voltage or more precisely, a voltage drop. When measuring resistance with an analog multimeter , switch off power to the circuit under measurement. Then place the red and black test pins in contact with both ends of the circuit under measurement and read the value indicated by the meter.

The voltage drop across a resistor in a simple circuit equals the voltage output of the battery. Calculate the effective resistance of a pocket calculator that has a 1. What is the voltage drop in it when 5. What is the effect on the appliance? A power transmission line is hung from metal towers with glass insulators having a resistance of 1. What current flows through the insulator if the voltage is kV? Some high-voltage lines are DC.

Thus, if the voltage drop across the extension cord is large, the voltage drop across the appliance is significantly decreased, so the power output by the appliance can be significantly decreased, reducing the ability of the appliance to work properly.

Skip to main content. Search for:. Explain what an ohmic material is. Describe a simple circuit. Resistance and Simple Circuits. Example 1. Calculating Resistance: An Automobile Headlight What is the resistance of an automobile headlight through which 2. Making Connections: Conservation of Energy In a simple electrical circuit, the sole resistor converts energy supplied by the source into another form.