Determine the Resistance of Wire by Slide Wire Bridge || FAROOQ AFZAAL || FSC Part II ||

Episode Overview

• This episode provides a detailed practical demonstration of a physics experiment to determine the resistance of an unknown wire.
• The experiment utilizes a slide wire bridge, which operates on the principle of the Wheatstone bridge.
• The video walks through the required apparatus, the correct procedure for setting up the circuit, and the method for taking measurements.
• It concludes by showing how to perform the necessary calculations to find the wire's resistance and lists important precautions for the experiment.

Key Concepts

• Slide Wire Bridge: An instrument used to accurately measure an unknown electrical resistance. It consists of a wire of uniform resistance stretched over a meter scale, with gaps to connect known and unknown resistances.
• Wheatstone Bridge Principle: The underlying theory, which states that when the bridge is balanced (no current flows through the galvanometer), the ratio of resistances in the two arms is equal. The formula used is X/R = L₂/L₁, where X is the unknown resistance and R is the known resistance.
• Apparatus: The key components required for the experiment include the slide wire bridge, a galvanometer, a resistance box (for known resistance), a jockey, a power source (battery), a key (switch), and the unknown wire (Eureka wire).
• Balance Point (Null Point): The specific point on the slide wire where the jockey is placed and the galvanometer shows zero deflection. At this point, the bridge is balanced, and the lengths L₁ and L₂ can be measured to calculate the unknown resistance.
• Specific Resistance (Resistivity): The video also introduces the formula (ρ = X * A/L) to calculate the specific resistance of the wire material once the mean resistance (X) is determined.

Quotes

• At 01:06 - "Negative Terminal of cell Connect with Key" - providing clear, step-by-step instructions for wiring the primary circuit.
• At 02:45 - "Find out the position of Balance point where the Galvanometer neddle turn bck to zero" - explaining the central objective of the measurement process, which is to locate the null point on the wire.
• At 04:10 - "The Jockey should not be pressed to much while sliding it over wire." - highlighting a critical precaution to ensure the uniformity of the wire is not altered, which would affect the accuracy of the results.

Takeaways

• Verify Circuit Connections First: Before taking any readings, always confirm your circuit is wired correctly by touching the jockey to both ends of the slide wire. The galvanometer should show full deflections in opposite directions.
• Use Proper Jockey Technique for Accuracy: To avoid damaging the wire or introducing errors, gently tap the jockey at various points along the slide wire rather than pressing and dragging it firmly.
• Optimize for Precision by Centering the Balance Point: For the most reliable results, adjust the known resistance (R) from the resistance box so that the balance point is found near the middle of the wire (between 30 cm and 70 cm), as this minimizes the percentage error in length measurements.