What is the principle of post office box experiment?
Wheatstone bridge
Description of the instrument It is called a post office box because it was originally used by the postal department for the measurement of the resistance of the telegraph wires and cables.
What is the formula of post office box?
S=QPR.
A post box is a numbered box which are available on rent at certain major post offices. Every post box is allocated a number and only postal articles bearing that number are placed into that box.
Which wire is used in post office box?
The best material for resistance in post box resistor is Manganin. It is an alloy of copper (85%), Manganese (12%) and Nickel (2%).
What is the Wheatstone Bridge Principle? The Wheatstone bridge works on the principle of null deflection, i.e. the ratio of their resistances is equal, and no current flows through the circuit. Under normal conditions, the bridge is in an unbalanced condition where current flows through the galvanometer.
What is post office box explain how does it work class 12 physics?
Answer: Post Office Box, Physics named it so because it has a shape of box and was designed to find resistance of electric cables and telegraph wires. Coils of wire are wound non-inductively, mounted in the body of the box, and have a negligible temperature coefficient.07-Feb-2021
A meter bridge is an electrical apparatus that is used to measuring the unknown resistance of a conductor. It consists of a wire of length one meter. Hence it is called a meter bridge.26-Sept-2021
Why is Wheatstone bridge used?
The Wheatstone bridge illustrates the concept of a difference measurement, which can be extremely accurate. Variations on the Wheatstone bridge can be used to measure capacitance, inductance, impedance and other quantities, such as the amount of combustible gases in a sample, with an explosimeter.
Instead the apparatus, composed of four resistors, a battery and a galvanometer, was named for the man who popularized it — Sir Charles Wheatstone. A scientist and mathematician, Samuel Hunter Christie, developed the circuit to measure unknown electrical resistances and first described it in 1833.10-Dec-2014
What is the purpose of Wheatstone?
The Wheatstone bridge is an electrical bridge circuit used to measure resistance. It consists of a common source of electrical current (such as a battery) and a galvanometer or a multimeter that connects two parallel branches, containing four resistors, three of which are known.
In a metre bridge, wires of nichrome, manganin and constantan are used because it has high resistance and low-temperature coefficient of resistance.
What is null point in meter bridge?
In a metre bridge experiment, null point is obtained at 20 cm from one end of the wire when resistance X is balanced against another resistance Y. If X < Y, then where will be the new position of the null point from the same end, if one decides to balance a resistance of 4X against Y? A. 50 cm. Right on!
Why thick copper strips are used in meter bridge? The connection between the resistors in the metre bridge is done using thick copper wires. Copper has very low resistivity. By using thick copper wires the resistivity is reduced further.
What is the formula of Metre bridge?
ρ=Lπr2X ; Where L be the length of the wire and r be its radius.
The reason why this bridge is called the Meter Bridge is because of the fact that it works on the Wheatstone bridge's principle. So, people also popularly call it Wheatstone's meter bridge. Another thing is that the wire length used in this circuit is 1 meter, so it has got its name as a meter bridge.
Which type of galvanometer is used in Wheatstone bridge?
A sensitive galvanometer is used to to detect when the Bridge circuit is 'balanced', by sensing the current (not voltage!) passing through it in a Wheatstone bridge .08-Feb-2015
Whetstone's bridge is an instrument which is used to determine the unknown resistance R other given resistances.06-Feb-2020
What is bridge sensitivity?
In electrical terms, bridge sensitivity is defined as the amount of deflection of the attached galvanometer per unit change in unknown resistance present in the circuit.
rheostat, adjustable resistor used in applications that require the adjustment of current or the varying of resistance in an electric circuit. The rheostat can adjust generator characteristics, dim lights, and start or control the speed of motors.
Which metal is used in meter bridge?
Generally alloys maganin/ constantan/ nichrome/ eureka are used in Meter Bridge, because these materials have low temperature coefficient of resistivity.
What is the principle of post office box experiment?