Measuring Voltage, Current & Resistance Flashcards
Define voltage and give its units of measurement
Voltage is the force that causes electrons to flow in a circuit.The basic usit of measurement is the volt; symbol V (sometimes E)
Describe how to connect a voltmeter in a circuit
to correctly measure voltage
The voltmeter is connected in parallel with the circuit. This means that the voltmeter does not draw any current from the circuit and thus does not affect the voltage measurement. The voltmeter is connected to the two points in the circuit where you want to measure the voltage drop.
Describe how voltage works in series and
parallel circuits
In a series circuit, voltage is shared between components, while in a parallel circuit, voltage is the same across all components:
Series circuit
The total voltage of the power supply is split between the components in proportion to their resistance. The current is the same through each component, and the total resistance is the sum of the individual resistances.
Parallel circuit
The voltage across each component is the same, and the total current is the sum of the currents through each component. The total resistance is less than the resistance of the smallest individual resistor.
Define current and give its units of measurement
Current is the rate at which electrons flow past a point in a complete electrical circuit. The basic unit of measurement is an Ampere (amp), symbol A.
Describe how to use an ammeter to measure current
An ammeter measures the current flow through a component or part of a circuit. The ammeter is placed in series with the device or section to be measured. The black wire is connected to common port on the ammeter. There are two ports for the red wire. Start with the 10 A port unless you know the current is in the milliamp range.
Describe the current characteristics in series and
parallel circuits
Current in a series circuit is the same through all loads
Current in a parallel circuit is divided between loads.
Define resistance and give its units of measurement
Resistance is a measure of the opposition to current flow in an electrical circuit. Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance.
Describe how resistance and continuity is measured
in series and parallel circuits
Resistance and continuity in series and parallel circuits can be measured using a multimeter. Measure the resistance or continuity from one point to another using a DMM. Make sure that there is no alternate path for current to flow.
Describe how a voltage drop is measured in a
series and parallel circuit
Voltage drop is the decrease in electric potential that occurs when current flows through a circuit’s resistance. It can be measured in both series and parallel circuits using a Digital Volt Ohm Meter (DVOM) or Digital Multi-meter’s DC voltage scale:
Series circuits
In a series circuit, the voltage drop across each component is the same percentage of the applied voltage. To calculate the voltage drop across a resistor in a series circuit, you can use Ohm’s law, which states that voltage drop (V) is equal to current (I) multiplied by resistance (R): V = I * R. You can also determine the percentage of a resistor’s value to the total resistance by dividing the resistor’s value by the total resistance and multiplying by 100. Then, multiply that percentage by the applied voltage to get the voltage across the resistor.
Parallel circuits
In a parallel circuit, the voltage across each component is the same. To measure voltage in a parallel circuit, touch one lead of the meter to one end of a resistor and the other lead to the other end of the same resistor. Both resistors should read the same voltage drop
Describe how to measure amperage in a series
and parallel circuit
Place an ammeter in series with the component to be measured.
Current will be the same in components connected in series.
Current will be split between components connected in parallel.
Describe how to measure resistance of a single component
Place the leads in parallel with the component or disconnect it from the circuit and measure across the terminals with an ohmmeter or DMM.
Measure the resistance in series and parallel circuits
Measure the resistance or continuity from one point to another using a DMM. Make sure there is no alternate path for current to flow.
