State Kirchhoff's law for an electrical network. Using these laws deduce the condition for balance in a Wheatstone bridge.

Kirchhoff's two rules are as under: (a) Junction rule: At any junction, the sum of the currents entering the junction is equal to the sum of currents leaving the junction. (b) Loop rule: The algebraic sum of changes in potential around any closed loop involving resistors and cells in the loop is zero. The circuit diagram for Wheatstone bridge is as under: This bridge has four resistors R 1 , R 2 , R 3 and R 4 . Across one pair of diagonally opposite points, that is points A and C , a source is connected. This is called the battery arm. Between the other two vertices, B and D , a galvanometer G is connected. This is called the galvanometer arm. There will be currents flowing across all the resistors as well as a current I g through G . In the case of a balanced bridge, the resistors are such that I g = 0 . In this case, Kirchhoff's junction rule is applied to junctions D and B . Now, we apply Kirchhoff's loop rule to closed loops A D B A and C B D C . The loop A D B A gives, - I 1 R 1 + 0 + I 2 R 2 = 0 ( ∵ I g = 0 ) ∴ I 1 R 1 = I 2 R 2 or I 1 I 2 = R 2 R 1 ...(a) And the loop C B D C gives, I 4 R 4 + 0 - I 3 R 3 = 0 ( ∵ I g = 0 ) ∴ I 3 R 3 = I 4 R 4 or I 3 I 4 = R 4 R 3 ....(b) Now, let the current entering A be I then it divides into I 1 and I 2 such that, I 2 = I - I 1 . The current I 2 further divides into I g and I 4 such that I 4 = I 2 - I g . In the case of a balanced bridge, I g = 0 therefore, I 4 = I 2 . Similarly, we get I 3 = I 1 . Substituting I 3 = I 1 and I 4 = I 2 in the equation (b) we get, I 1 I 2 = R 4 R 3 ...(c) From the equations (a) and (c), we get, I 1 I 2 = R 2 R 1 = R 4 R 3 Hence, we obtain the condition, R 2 R 1 = R 4 R 3 which is the equation relating the four resistors called the balance condition for the galvanometer to give zero or null deflection.

EASY

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IMPORTANT

Earn 100

Show the variation of current versus voltage graph for $GaAs$ and mark the (i) Non-linear region (ii) Negative resistance region.

Important Questions on Current Electricity

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IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 13

A student has two wires of iron and copper of equal length and diameter. He first joins two wires in series and passes an electric current through the combination which increases gradually. After that he joins two wires in parallel and repeats the process of passing current. Which wire will glow first in each case?

MEDIUM

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IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 14

Three identical resistors are connected in parallel and total resistance of the circuit is

\frac{R}{3}

. Find the value of each resistance.

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IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 1

What is the condition in which the heat produced in an electric circuit is :

(a) directly proportional

(b) inversely proportional

to the resistance of the circuit?

Compute the ratio of the total quantity of heat produced in the two cases.

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IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 2

Two metallic wires

A

and

B

are connected in parallel. Wire

A

has length

L

and radius

r

. Wire

B

has length

2 L

and radius

2 r

. Compute the ratio of the total resistance of the parallel combination and resistance of wire

A

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IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 3

In a house, three bulbs of

100 W

each are lighted for

4

hours daily and six tube lights of

20 W

each are lighted for

5

hours daily and a refrigerator of

400 W

is worked for

10

hours daily for a month of

30

days. Calculate the electricity bill if the cost of one unit is

₹ 4.00

MEDIUM

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IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 4

Three resistors of

4

ohms,

6

ohms and

12

ohms are connected in parallel. The combination of the above resistors is connected in series to a resistance of

2

ohms and then to a battery of

6

volts. Draw a circuit diagram and calculate the current in the main circuit.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 4

Three resistors of

4

ohms,

6

ohms and

12

ohms are connected in parallel. The combination of the above resistors is connected in series to a resistance of

2

ohms and then to a battery of

6

volts. Draw a circuit diagram and calculate the current flowing through each of the resistors in parallel.

MEDIUM

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 6 - Current Electricity>MODEL QUESTIONS (IPE PATTERN)>Q 4

Three resistors of

4

ohms,

6

ohms and

12

ohms are connected in parallel. The combination of the above resistors is connected in series to a resistance of

2

ohms and then to a battery of

6

volts. Draw a circuit diagram and calculate the potential difference and the power used by the

2

ohm resistor.

Show the variation of current versus voltage graph for GaAs and mark the (i) Non-linear region (ii) Negative resistance region.

Important Questions on Current Electricity

Learn and Prepare for any exam you want !

Show the variation of current versus voltage graph for $GaAs$ and mark the (i) Non-linear region (ii) Negative resistance region.