Wheatstone Bridge : The Wheatstone bridge is used to calculate unknown resistances. The variable resistance R3 is adjusted until the galvanometer reads zero with the switch closed. This simplifies the circuit, allowing Rx to be calculated based on the IR drops. The potential difference between points b and d is then zero, meaning that b and d are at the same potential. With no current running through the galvanometer, it has no effect on the rest of the circuit.
So the branches abc and adc are in parallel, and each branch has the full voltage of the source. Since b and d are at the same potential, the IR drop along ad must equal the IR drop along ab. Again, since b and d are at the same potential, the IR drop along dc must equal the IR drop along bc. This equation is used to calculate the unknown resistance when current through the galvanometer is zero. This method can be very accurate, but it is limited by two factors.
First, it is not possible for the current through the galvanometer to be exactly zero. Second, there are always uncertainties in R 1 , R 2 , and R 3 , which contribute to the uncertainty in R x.
Privacy Policy. Skip to main content. Circuits and Direct Currents. Search for:. Voltmeters and Ammeters. Voltmeters and Ammeters Voltmeters and ammeters are used to measure voltage and current, respectively. Learning Objectives Compare circuit connection of an ammeter and a voltmeter. Key Takeaways Key Points A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit.
An ammeter is a measuring device used to measure the electric current in a circuit. A voltmeter is connected in parallel with a device to measure its voltage, while an ammeter is connected in series with a device to measure its current. At the heart of most analog meters is a galvanometer, an instrument that measures current flow using the movement, or deflection, of a needle. The needle deflection is produced by a magnetic force acting on a current-carrying wire.
Key Terms shunt resistance : a small resistance R placed in parallel with a galvanometer G to produce an ammeter; the larger the current to be measured, the smaller R must be; most of the current flowing through the meter is shunted through R to protect the galvanometer galvanometer : An analog measuring device, denoted by G, that measures current flow using a needle deflection caused by a magnetic field force acting upon a current-carrying wire.
Voltmeter : Demonstration voltmeter from a physics class. Null Measurements Null measurements balance voltages so there is no current flowing through the measuring devices that would interfere with the measurement. Learning Objectives Explain why null measurements are employed. Key Takeaways Key Points Measurements of voltages and current with standard voltmeters and ammeters alter the circuit being measured, introducing uncertainties. Null measurements are employed to reduce the uncertainty in the measured voltage and current.
The potentiometer and the Wheatstone bridge are two methods for making null measurements. The potentiometer is an instrument that measures an unknown voltage by opposing with a known voltage, without drawing current from the voltage source being measured.
A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. Key Terms null measurements : methods of measuring current and voltage more accurately by balancing the circuit so that no current flows through the measurement device potentiometer : an instrument that measures a voltage by opposing it with a precise fraction of a known voltage, and without drawing current from the unknown source.
Wheatstone bridge : An instrument used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. You need to know how to measure the current that flows through a component in a circuit and the voltage across it. Current is measured in amperes.
Amperes is often abbreviated to amps or A. The current flowing through a component in a circuit is measured using an ammeter. Digital multimeters have multiple measurement parameters such as voltage, resistance, current, etc. First, set the rotary switch to voltage. In the case of DC voltage, the unit of voltage "V" and the mark indicating DC are displayed as shown in the figure.
Insert the black test lead into the COM terminal of the digital multimeter. Also insert the red test lead into the terminals labeled "V and "mV". To ensure accurate measurement, zero adjustment is recommended to be performed before measurement.
Voltage measurement terminal. In this way, you can measure the voltage value. You can select a measurement range for voltage measurement. Select the range. If you need to change the range, move the test leads away from the circuit under measurement first. Changing the range while the leads are in contact with the circuit could damage the instrument. Exercise care to only place the leads in contact with the intended area. You may need to measure voltage in order to check the safety or quality of an electronic device.
Testers multimeters are necessary in order to measure voltage.
0コメント