- Introduction
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- ElectroMotive Force(emf)
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- Internal Resistance of Battery (or cell)
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- Electric Energy and Power
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- Kirchoff's Rules
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- The junction Rule (or point rule)
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- The Loop Rule (or Kirchoff's Voltage Law)
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- Grouping of the cell's
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- Meterbridge (slide wire bridge)
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- Potentiometer
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- Comparison of EMF's of two cells using potentiometer
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- Determination of internal resistance of the cell

- Meter bridge is based on the principle of wheatstone bridge and it is used to find the resistance of an unknown conductor or to compare two unknown

resistance

- Figure below shows a schematic diagram of a meter bridge

- In above figure AC is a 1m long wire made of maganin or constanan having uniform area of cross-section

- This wire is stretched along a scale one a wooden base

- Ends A and C of the wire are screwed to two L shaped copper strips as shown in figure

- A resistance box R and an unknown resistance S are connected as shown in figure

- One terminal of galvanometer is connected to point D and another terminal is joined to a jockey that can be slided on a bridge wire

- when we adjust the suitable resistance of value R in the resistance box and slide this jockey along the wire then a balance point is obtained sat at point B

- Since the circuit now is the same as that of wheatstone bridge ,so from the condition of balanced wheatstone bridge we have

P/Q=R/S

Here resistance P equals

P=ρl_{1}/A

And Q=ρl_{2}/A

where ρ is the resistivity of the material of the wire and A is the area of cross-section of wire

Now P/Q=(ρl_{1}/A)(A/ρl_{2})=l_{1}/l_{2}

- Potentiometer is an accurate instruments used to compare emf's of a cells,Potential difference between two points of the electric wire

- Potentiometer is based on the principle that potential drop across any portion of th wire of uniform crossection is proportional to the length of that portion of thw wire when a constant current flows through the wire

- Figure below shows the construction of a potentiometer which consists of a number of segments of wire of uniform area of cross-section stretched on a wooden board between two copper strips .Meter scale is fixed parallel to the lenght of the wire

- A battery is connected across terminals A and B through a rehestat so that a constant currents flows through the wire

- Potentiometer is provided with a jockey J with the help of which contact can be made at any point on the wire

- Suppose A and ρ are the area of cross-section and resistivity of the material of the wire the resitance

R=ρl/A ----------------------------(i)

where l is the lenght of the wire

- If I is the current flowing through the wire then from Ohm's Law,

V=IR ------------------------------(ii)

Where V is the potential differene across the position of the wire of length l

Thus ,from (i) and (ii)

V=IR=I(ρl/A)=kl

where K=ρI/A

=> V is proportional to l when current I is constant

- K=V/l is also known as potential gradient which is the fall of potential per unit length of wire

- Senstivity of a potentiometer depends on its potential gradient .If the potential gradient of a potentiometer is small then the potentiometer is more sensitive and hence more accurate

Class 12 Maths Class 12 Physics

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