Current Electricity is an important topic from JEE Main / JEE Advanced Exam Point of view. Every year there are 1-3 questions asked from this topic. This short notes on Current Electricity will help you in revising the topic before the JEE Main & IIT JEE Advanced Exam. This is the third part of Current Electricity in which we have discussed Electric Instruments.
Wheatstone bridge, Meter Bridge, and Potentiometer
Wheatstone bridge
The above shown arrangement is a case of Wheatstone bridge.
For balanced condition: the current in the arm BD is zero, i.e. there will be no deflection in the galvanometer G.
Wheat stone bridges are used in calculation of unknown resistances.
Meter Bridge
It consists of a wire of length 1m. and of uniform cross sectional area strained tight and fastened between two thick metallic strips fixed at right angles.
The end points are connected to a cell through a key and one end of a galvanometer is connected to the metallic strip midway between the two gaps. The other end of the galvanometer is connected to a ‘jockey’ as in the figure.
It uses the balanced Wheatstone bridge to determine the unknown resistance:
Potentiometer
An instrument which has several metre long wire connected across a cell. The potentiometer draws no current from the voltage source is measured because it is unaffected by the internal resistance of the source. It is used to compare the Emf’s of a cell and the unknown internal resistance of the cell.
Principle: When a constant current flows through a uniform cross sectional wire the potential difference between two points is directly proportional to the length of the wire between the two points.
Applications of Potentiometer
Comparing the Emf of the cell: The Emf of a cell is compared by observing the balancing length
From the principle:
Comparing the Internal resistance of the cell:
As it draws no current from voltage source the internal resistance of any cell is measured using the potentiometer by finding the balancing lengths for the cell.
Worried about JEE 2020? Join our One Year Master Course to Crack JEE 2020: StepUp JEE 2020: A One-Year Master Course
StepUp JEE 2020: A One-Year Master Course
Thanks
Team BYJU'S Exam Prep!!
The Most Comprehensive Exam Prep App.
Comments
write a comment