Class 9 > Unit # 01: Physical Quantities & Measurement > Physical Balance & Electronic Balance

Talha's Physics Academy

Chapter # 1: Physical Quantities and Measurements — Physical & Electronic/Digital Balance

Lecture Overview

This comprehensive lecture from Talha's Physics Academy covers the fundamental instruments used to measure mass in physics, detailing the construction, working principles, components, and operation methods for the Physical Balance and the Electronic/Digital Balance.

Source Video: Physical & Electronic/Digital Balance | Chapter 01 | Physical Quantities and Measurements | Class 9

1. Physical Balance

A physical balance is a sensitive laboratory instrument used to measure the mass of various objects by comparison with standard masses.

• Working Principle: Operates on the principle of moments, where the system is balanced when the torque produced by the object on one side equals the torque produced by the standard weights on the other side (\(\tau_1 = \tau_2\)).
• Construction & Key Components:
  • A light and rigid metallic beam resting at the center on a pillar.
  • Two pans placed on either side (the left pan is typically used for the object, and the right pan for standard weights).
  • A pointer attached to the beam moving over a fixed scale to indicate equilibrium.
  • A plumb line to check vertical alignment and leveling screws at the base to adjust level.
  • Housed inside a glass box to eliminate errors caused by air currents.

$$\text{Principle of Moments: } \tau_{\text{left}} = \tau_{\text{right}}$$

2. Electronic/Digital Balance

An electronic balance is a modern precision instrument used to measure mass quickly and accurately using integrated electronic circuits.

• Sensitivity Ranges: Available in various sensitivities, capable of measuring down to milligrams, grams, kilograms, or even micro-grams for high-precision applications.
• Operation Procedure:
  • Turn on the balance and press the tare/zero button to reset the display to zero (\(0\)).
  • Place any container or the object directly onto the pan.
  • Read the precise mass value shown on the digital screen along with its measurement unit.

$$\text{Digital Mass Readout} = \text{Direct Value on Screen}$$

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