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CURRENT  ELECTRICITY - II
1. Kirchhoff’s Laws of electricity
2. Wheatstone Bridge
3.   Metre Bridge
4. Potentiometer
i)  Principle
ii) Comparison of emf of primary cells
Page 2


CURRENT  ELECTRICITY - II
1. Kirchhoff’s Laws of electricity
2. Wheatstone Bridge
3.   Metre Bridge
4. Potentiometer
i)  Principle
ii) Comparison of emf of primary cells
KIRCHHOFF’S LAWS:
I Law or Current Law or Junction Rule:  
The algebraic sum of electric currents at a junction in any 
electrical network is always zero.
O
I
1
I
4
I
2
I
3
I
5
I
1
- I
2
- I
3
+ I
4
- I
5
= 0
Sign Conventions:
1. The incoming currents towards the junction are taken positive.
2. The outgoing currents away from the junction are taken negative.
Note:  The charges cannot accumulate at a junction.  The number 
of charges that arrive at a junction in a given time must leave in 
the same time in accordance with conservation of charges.
Page 3


CURRENT  ELECTRICITY - II
1. Kirchhoff’s Laws of electricity
2. Wheatstone Bridge
3.   Metre Bridge
4. Potentiometer
i)  Principle
ii) Comparison of emf of primary cells
KIRCHHOFF’S LAWS:
I Law or Current Law or Junction Rule:  
The algebraic sum of electric currents at a junction in any 
electrical network is always zero.
O
I
1
I
4
I
2
I
3
I
5
I
1
- I
2
- I
3
+ I
4
- I
5
= 0
Sign Conventions:
1. The incoming currents towards the junction are taken positive.
2. The outgoing currents away from the junction are taken negative.
Note:  The charges cannot accumulate at a junction.  The number 
of charges that arrive at a junction in a given time must leave in 
the same time in accordance with conservation of charges.
II Law or Voltage Law or Loop Rule:
The algebraic sum of all the potential drops and emf’s along any 
closed path in an electrical network is always zero.
Sign Conventions:
1. The emf is taken negative when we traverse from positive to negative
terminal of the cell through the electrolyte.
2. The emf is taken positive when we traverse from negative to positive
terminal of the cell through the electrolyte.
The potential falls along the direction of current in a current path 
and it rises along the direction opposite to the current path.  
3. The potential fall is taken negative.
4. The potential rise is taken positive.
Loop ABCA:
- E
1
+ I
1
.R
1
+ (I
1
+ I
2
).R
2
= 0
E
1
R
1
E
2
R
3
R
2
I
1
I
2
I
1
I
2
I
1
I
2
I
1
+ I
2
A
B
C
D
Note: The path can be traversed 
in clockwise or anticlockwise 
direction of the loop.
Loop ACDA:
- (I
1
+ I
2
).R
2
- I
2
.R
3
+  E
2
= 0
Page 4


CURRENT  ELECTRICITY - II
1. Kirchhoff’s Laws of electricity
2. Wheatstone Bridge
3.   Metre Bridge
4. Potentiometer
i)  Principle
ii) Comparison of emf of primary cells
KIRCHHOFF’S LAWS:
I Law or Current Law or Junction Rule:  
The algebraic sum of electric currents at a junction in any 
electrical network is always zero.
O
I
1
I
4
I
2
I
3
I
5
I
1
- I
2
- I
3
+ I
4
- I
5
= 0
Sign Conventions:
1. The incoming currents towards the junction are taken positive.
2. The outgoing currents away from the junction are taken negative.
Note:  The charges cannot accumulate at a junction.  The number 
of charges that arrive at a junction in a given time must leave in 
the same time in accordance with conservation of charges.
II Law or Voltage Law or Loop Rule:
The algebraic sum of all the potential drops and emf’s along any 
closed path in an electrical network is always zero.
Sign Conventions:
1. The emf is taken negative when we traverse from positive to negative
terminal of the cell through the electrolyte.
2. The emf is taken positive when we traverse from negative to positive
terminal of the cell through the electrolyte.
The potential falls along the direction of current in a current path 
and it rises along the direction opposite to the current path.  
3. The potential fall is taken negative.
4. The potential rise is taken positive.
Loop ABCA:
- E
1
+ I
1
.R
1
+ (I
1
+ I
2
).R
2
= 0
E
1
R
1
E
2
R
3
R
2
I
1
I
2
I
1
I
2
I
1
I
2
I
1
+ I
2
A
B
C
D
Note: The path can be traversed 
in clockwise or anticlockwise 
direction of the loop.
Loop ACDA:
- (I
1
+ I
2
).R
2
- I
2
.R
3
+  E
2
= 0
Wheatstone Bridge:
I
1
I
I
g
I
1
- I
g
I - I
1
E
A
B
C
D
P
Q
R
S
G
I
I I
I - I
1 
+ I
g
Loop ABDA:
-I
1
.P - I
g
.G + (I - I
1
).R = 0
Currents through the arms are assumed by 
applying Kirchhoff’s Junction Rule.
Applying Kirchhoff’s Loop Rule for:
When I
g
= 0, the bridge is said to balanced. 
By manipulating the above equations, we get
Loop BCDB:
- (I
1
- I
g
).Q + (I - I
1
+ I
g
).S + I
g
.G = 0
P
Q
R
S
Page 5


CURRENT  ELECTRICITY - II
1. Kirchhoff’s Laws of electricity
2. Wheatstone Bridge
3.   Metre Bridge
4. Potentiometer
i)  Principle
ii) Comparison of emf of primary cells
KIRCHHOFF’S LAWS:
I Law or Current Law or Junction Rule:  
The algebraic sum of electric currents at a junction in any 
electrical network is always zero.
O
I
1
I
4
I
2
I
3
I
5
I
1
- I
2
- I
3
+ I
4
- I
5
= 0
Sign Conventions:
1. The incoming currents towards the junction are taken positive.
2. The outgoing currents away from the junction are taken negative.
Note:  The charges cannot accumulate at a junction.  The number 
of charges that arrive at a junction in a given time must leave in 
the same time in accordance with conservation of charges.
II Law or Voltage Law or Loop Rule:
The algebraic sum of all the potential drops and emf’s along any 
closed path in an electrical network is always zero.
Sign Conventions:
1. The emf is taken negative when we traverse from positive to negative
terminal of the cell through the electrolyte.
2. The emf is taken positive when we traverse from negative to positive
terminal of the cell through the electrolyte.
The potential falls along the direction of current in a current path 
and it rises along the direction opposite to the current path.  
3. The potential fall is taken negative.
4. The potential rise is taken positive.
Loop ABCA:
- E
1
+ I
1
.R
1
+ (I
1
+ I
2
).R
2
= 0
E
1
R
1
E
2
R
3
R
2
I
1
I
2
I
1
I
2
I
1
I
2
I
1
+ I
2
A
B
C
D
Note: The path can be traversed 
in clockwise or anticlockwise 
direction of the loop.
Loop ACDA:
- (I
1
+ I
2
).R
2
- I
2
.R
3
+  E
2
= 0
Wheatstone Bridge:
I
1
I
I
g
I
1
- I
g
I - I
1
E
A
B
C
D
P
Q
R
S
G
I
I I
I - I
1 
+ I
g
Loop ABDA:
-I
1
.P - I
g
.G + (I - I
1
).R = 0
Currents through the arms are assumed by 
applying Kirchhoff’s Junction Rule.
Applying Kirchhoff’s Loop Rule for:
When I
g
= 0, the bridge is said to balanced. 
By manipulating the above equations, we get
Loop BCDB:
- (I
1
- I
g
).Q + (I - I
1
+ I
g
).S + I
g
.G = 0
P
Q
R
S
Metre Bridge:
A B
R.B (R)
X
G
J
K
E
l cm 100 - l cm
Metre Bridge is based 
on the principle of 
Wheatstone Bridge.
When the galvanometer 
current is made zero by 
adjusting the jockey 
position on the metre-
bridge wire for the given 
values of known and 
unknown resistances,
R       R
AJ
X        R
JB
R       AJ
X       JB
R          l
X       100 - l
(Since, 
Resistance a
length)
Therefore,            X = R (100 – l) / l
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157 videos|453 docs|185 tests

FAQs on PPT: Current Electricity - 2 - Physics Class 12 - NEET

1. What is current electricity?
Ans. Current electricity refers to the flow of electric charge in a conductor. It is the movement of electrons in a closed circuit, which is usually produced by a power source such as a battery or a generator.
2. How is current measured?
Ans. Current is measured using a device called an ammeter. The ammeter is connected in series with the circuit, and it measures the amount of current flowing through the circuit in amperes (A).
3. What is the difference between AC and DC current?
Ans. AC (alternating current) and DC (direct current) are two types of current electricity. The main difference is that AC changes direction periodically, while DC flows in only one direction. AC is commonly used in household power supply, while DC is used in batteries and electronic devices.
4. What is Ohm's Law?
Ans. Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage across it, and inversely proportional to its resistance. It can be mathematically represented as I = V/R, where I is the current, V is the voltage, and R is the resistance.
5. How does a circuit breaker work?
Ans. A circuit breaker is a safety device used to protect electrical circuits from damage caused by overloading or short circuits. When the current in a circuit exceeds a certain limit, the circuit breaker automatically opens, interrupting the flow of electricity and preventing damage to the circuit.
157 videos|453 docs|185 tests
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