How do the working principles of a voltmeter and an electrometer differ?

Voltmeter and electroscope, although both are instruments used to measure electrical quantities, have significant differences in their working principles and uses.

The working principle of the voltmeter

Voltmeter is mainly used to measure the potential difference (voltage) between two points in a circuit. Its working principle is based on electromagnetic induction and the effect of current. Common voltmeters include magnetoelectric voltmeter and digital voltmeter.

1. Magnetoelectric Voltmeter: This type of voltmeter indirectly measures voltage by measuring current. When current flows through the coil of the voltmeter, it generates a torque in the magnetic field, causing the pointer to deflect. The angle of deflection is directly proportional to the current, and since the current is also directly proportional to the voltage, the angle of deflection of the pointer reflects the magnitude of the voltage.

2. Digital Voltmeter: This type of voltmeter measures voltage by converting analog signals into digital signals. Analog-to-digital converters (ADCs) are commonly used to convert voltage signals into digital form, which is then displayed on a screen.

The working principle of the electroscope

A static meter (also known as a potential difference meter or pointer electroscope) is an instrument used to measure potential difference, but it operates differently from a voltmeter. The working principle of a static meter is based on electrostatic induction and the interaction of charges.

1. Electrostatic Induction: The metal ball and metal rod of the electroscope form a capacitor. When a charged object is brought near the electroscope, charges are induced on the metal ball and rod, causing the needle to deflect.

2. Charge Interaction: The deflection of the pointer in an electroscope is due to the mutual repulsion of like charges. When a charged object is brought near, the induced charge causes the pointer to deflect, and the angle of deflection is directly proportional to the potential difference.

Main Differences

Measurement Method:

The voltmeter indirectly measures voltage by measuring current.

The electrostatic meter measures the potential difference directly through electrostatic induction and charge interaction.

Structure and Design:

• Voltmeters typically consist of a coil and a magnetic field, generating torque through the flow of current.

The electroscope, on the other hand, consists of a metal ball and metal rod, which generate charge through electrostatic induction, causing the needle to deflect.

Application Scenarios:

• Voltmeters are suitable for measuring voltages in circuits, especially in dynamic circuits.

• Electrostatic meters are suitable for measuring static electric fields and are often used to demonstrate electrostatic phenomena and measure potential differences.

In summary, there are significant differences between the working principles, structural designs, and application scenarios of voltmeters and electroscopes. Voltmeters measure voltage by measuring current, while electroscopes measure potential difference through electrostatic induction and charge interaction.