Advertisements
Advertisements
प्रश्न
Explain the determination of unknown resistance using meter bridge.
उत्तर
The meter bridge is another form of Wheatstone’s bridge. It consists of a uniform manganin wire AB of one meter length. This wire is stretched along a meter scale on a wooden board between two copper strips C and D. Between these two copper strips another copper strip E is mounted to enclose two gaps G1 and G2 An unknown resistance P is connected in G1 and a standard resistance Q is connected in G2.
A jockey (conducting wire) is connected to the terminal E on the central copper strip through a galvanometer (G) and a high resistance (HR). The exact position of jockey on the wire can be read on the scale. A Lechlanche cell and a key (K) are connected across the ends of the bridge wire.
Meter bridge
The position of the jockey on the wire is adjusted so that the galvanometer shows zero deflection. Let the point be J. The lengths AJ and JB of the bridge wire now replace the resistance R and S of the Wheatstone’s bridge. Then
`"P"/"Q" = "R"/"S" = ("R"' *"AJ")/("R"'*"JB")` ....(1)
where R’ is the resistance per unit length of wire
`"P"/"Q" = "AJ"/"JB" = l_1/l_2` ....(2)
P = Q `l_1/l_2` ....(3)
The bridge wire is soldered at the ends of the copper strips. Due to imperfect contact, some resistance might be introduced at the contact. These are called end resistances. This error can be eliminated, if another set of readings are taken with P and Q interchanged and the average value of P is found.
To find the specific resistance of the material of the wire in the coil P, the radius r and length l of the wire is measured. The specific resistance or resistivity r can be calculated using the relation.
Resistance = ρ - `l/"A"`
By rearranging the above equation, we get
ρ = Resistance `xx "A"/l`
If P is the unknown resistance, equation (4) becomes
ρ = P`(pi"r"^2)/l`
APPEARS IN
संबंधित प्रश्न
The current is drawn from a cell of emf E and internal resistance r connected to the network of resistors each of resistance r as shown in the figure. Obtain the expression for
- the current draw from the cell and
- the power consumed in the network.
Determine the equivalent resistance of networks shown in Fig.
Determine the equivalent resistance of networks shown in Fig.
State the principle of potentiometer.
The instrument for the accurate measurement of the e.m.f of a cell is ______.
Kirchhoff’s second law is a consequence of law of conservation of ______.
Two cell of 1.25 V and 0.75 V are connected parallel. The effective voltage will be:-
In a meter bridge the point D is a neutral point (Figure).
- The meter bridge can have no other neutral point for this set of resistances.
- When the jockey contacts a point on meter wire left of D, current flows to B from the wire.
- When the jockey contacts a point on the meter wire to the right of D, current flows from B to the wire through galvanometer.
- When R is increased, the neutral point shifts to left.
A 6-volt battery is connected to the terminals of a three-metre-long wire of uniform thickness and resistance of 100 ohms. The difference of potential between two points on the wire separated by a distance of 50 cm will be ______.
The figure below shows two batteries, E1 and E2, having emfs of 18V and 10V and internal resistances of 1 Ω and 2 Ω, respectively. W1, W2 and W3 are uniform metallic wires AC, FD and BE having resistances of 8 Ω, 6 Ω and 10 Ω respectively. B and E are midpoints of the wires W1 and W2. Using Kirchhoff's laws of electrical circuits, calculate the current flowing in the wire W3:
