Electric Current | Visual Physics for IIT JEE / NEET
Electric Current

Is electric current flow of charge ? Is current a vector quantity ?

Q1

In an experiment, there is a stream of Helium nucleus drifting across a cross section of tube while the electrons drift in opposite direction. Number of Helium nucleus crossing the area per second is 1016, while the number of electrons drifting in the opposite direction is 1020 per second. Find the current flowing in the tube.

Q2

A current of 10 A is maintained in a wire for 32 s. In this time a) how much charge and b) how many electrons flow through the wire ?

Current Density

What is current density ? Is current density a vector quantity ? Can we treat current density like streamlines in a flow ?

Resistance Resistivity

What is Resistance ? And what is the cause of resistance ? Does resistance depend on temperature ?

Q3

A wire of mass m, length l and area of cross section A is stretched in such a way that its length increases by 10 % of its original value. What is the percent change in resistance ?

Q4

Two wires of same dimensions but resistivity r1 and r2 are connected in a) series b) parallel Find the equivalent resistivity of the combinations.

Q5

Two wires of same dimensions but resistivity r1 and r2 are connected in a) series b) parallel Find the equivalent resistivity of the combinations.

Color Codes

Explanation of the color codes for resistors

Ohms Law

What is Ohms Law ? Is Ohms Law actually a \"Law\" ? Is Ohms Law always true ?

Drift Speed - 1

If the electrons are in constant random motion in all directions in a conductor, then how do we get current in one direction ? Do the electrons leave their random motion and all start moving in a particular direction ? What is Drift Speed ? And how do we calculate drift speed ?

Drift Speed - 2

How does drift speed depend on the area of cross-sector of conductor ? How does it depend on the length of conductor ?

Drift Speed - 3

Understanding Resistance, Resistivity, Mobility and Conductivity from Drift Speed

Q6

A copper wire has a square cross section of 6 mm on a side with free electron density of 8 x 10 28 / m3 . The wire is 5 m long and carries a current of 7.2 A. Find the magnitude of (a) the current density in wire; (b) the electric field in the wire. (c) How much time is required for and electron to travel the length of the wire ?

Q7

A copper wire have 4 x 1021 free electrons in 2 cm of its length, having drift speed of 0.05 cm/sec. How many electrons would pass through a given cross section of the wire each second. How large would a current be flowing in the wire?

Q8

a. A steady current flows in a metallic conductor of non - uniform cross section. State which of the quantities i.e. current , current density, electric field and drift velocity remains constant ? b. A steady current passes through a cylindrical conductor. Is there an electric field inside the conductor ?

Q9

A potential difference V is applied to copper wire of diameter d and length L. What will be the effect on the electron drift speed by doubling : (a) voltage V or (b) length L or (c) diameter d

Q10

The following table gives the length of three uniform copper rods, their diameters, and the potential differences between their ends. Rank the rods according to, (a) the magnitude of the electric field in them (b) the current density in them, and (c) the drift speed of electrons in them

Var with Temp

How does Resistivity and Resistance vary with temperature ?

Q11

a) A copper coil has a resistance of 50 W at 0o C and a resistance of 60 W at 120 o C. Find out the temperature coefficient of resistance of copper. b) A metallic wire has a resistance of 100 W at 20o C. Find the temperature at which the resistance of same metallic wire rises to 200 W. Temperature coefficient of wire is 2 ? 10-2 oC-1.

Q12

First figure shows the I - V graph for two metallic wires at constant temperature. Assuming that the wires have the same length and diameter, which of the two wires has a higher resistivity. Second figure shows the I - V graph for a metallic wire at two different temperatures T 1 and T 2. Which of the two temperatures T 1 and T 2 is higher ?

Resistor Combination

Equivalent Resistance of resistors connected in Series / Parallel

Q13

Two cubes of same material are connected to a battery as shown in figure. Find the ratio of a) their resistance b) potential difference across them

Q14

All resistances in the circuit shown below are in ohms. Find the effective resistance between points A and B.

Q15

In the given circuit, find equivalent resistance between points A and B. All resistances are in ohms. If an ideal battery with emf 70 V is connected between A and B, a) what will be the current supplied by battery ? b) potential drop across the 5 W resistor ?

Kirchhoffs Law

Kirchhoff?s Junction Rule and Kirchhoff?s Loop Rule for electrical circuits. Is Kirchhoff?s Junction rule derived from conservation of Charge ? Is Kirchhoff?s Loop Rule derived form Conservation of Energy ?

Q16

In the part of the circuit shown, find the potential difference between AB5

Q17

In the circuit shown in figure, all potentials are in Volts and resistances are in Ohms. Find the potential difference between points A and B.

Sym Type 1 - P1

Identification of certain types of symmetries in the circuit to simplify and solve circuits faster.

Sym Type 1 - P2

Application of certain types of symmetries in the circuit to simplify and solve circuits faster. Much more in-depth and informative discussion on Circuit Symmetry.

Q18

If each of the resistances in the shown network is R, then what is the resistance between A and B.

Q19

Find the equivalent resistance between points A and B.

Symmetry Type 2

Principle of Reversibility of a circuit. Next level of Symmetry of circuits to simplify and solve circuits faster. New types of symmetries rarely discussed in books. Much more in-depth and informative discussion on Circuit Symmetry.

Q20

Given that resistance of each resistor is R, find the equivalent resistance between AB.

Q21

Equivalent resistance between A and B is :

Battery

How does a Battery work ?

EMF and Potential

Difference between EMF , Voltage or Potential difference ?

Battery Combination

Equivalent Battery of a combination of batteries

Q22

In the circuit shown in figure, find the value of current i.

Ammeter

Ammeter is a device used to measure current in electrical circuits. How does an Ammeter work ?

Voltmeter

Voltmeter is a device used to measure voltage in electrical circuits. How does a Voltmeter work ?

Potentiometer - 1

What the limitations of a Voltmeter ? And how is Potentiometer a better device to measure voltage in a electrical circuits ? How does a Potentiometer work ?

Potentiometer - 2

How can a Potentiometer be used to compare the EMF of 2 batteries ?

Q23

Find the relation between the resistors so that there is no current in the middle resistor.

Wheatstone Bridge

How can a Wheatstone Bridge be used to find an unknown resistance ?

1

A non conducting ring of radius R has charge Q distributed evenly over it. If it rotates with an angular velocity w, the equivalent current will be

2

A uniform copper wire of mass 10 gm carries a current of 1 A when a potential difference of 10 V is applied across it. Calculate the length and the area of cross section. Given that density of copper is 10 103 kg/m3 and resistivity is 2 10-8 W m.

3

A copper wire of cross section area A is carrying a current I. Resistivity, density and atomic mass of copper is ro, d kg/m3 and m a.m.u respectively. Assuming that each copper atom contributes one free electron, find the (a) drift speed of the electrons in the wire (b) the average time between collisions for the electrons and (c) compare the drift speed obtained with the speed of propagation of electric field along the wire.

4

In the circuit shown in figure, find the potential difference across R1 and R2.

5

A parallel combination of an 8 W resistors and an unknown resistor R is connected in series with a 16 W resistor and a battery. The circuit is then disassembled and the three resistors are then connected in series with each other and the same battery. In both arrangements, the current through the 8 W resistor is the same. What is the unknown resistance R ?

6

In both the circuits shown below, current supplied by the battery is equal. Current though R in the second circuit is (1/10)th of current through R in the first circuit. Find the value of R1 and R2 in terms of R.

7

From the information given in the figure, find out the value of resistance R.

8

Find the current supplied by the battery in the circuit in each case.

9

Equivalent resistance between A and B is :

10

Consider an infinite ladder of network shown in the figure. a) Find the equivalent resistance of this circuit. b) Find the current in first R2 c) Suggest a method to terminate the circuit without changing its equivalent resistance d) If the voltage is halved after each section, find the ratio R1 / R2.

11

The circuit shown in figure extends till infinity. The resistance of the resistors in each subsequent element differs by a factor of K = 1/2 from the resistances of the resistors in the previous elements. Find the equivalent resistance of the circuit.

12

In the given circuit, equilateral triangular frames are embedded inside each other as shown in the figure. Corners of every inner triangle are at the mid-point of the sides of outer triangle. Find the resistance of system between points AB. Given that the number of successively embedded equilateral triangles tends to infinity, and that resistance of each wire is proportional to its length.

13

The effective resistance of the electrical circuit shown in figure is

14

If the resistance of each resistor in the circuit is R, then equivalent resistance between points A and B is a) 14 R b) R / 14 c) 1.2 R d) 7 R e) R / 7

15

Find the equivalent resistance between points A and B of the circuit shown in figure

16

Consider a cube of equal resistors on its edges. Find the equivalent resistance between points A and B for the two cases shown below.

17

Find the equivalent resistance between points A and B. Resistance of each edge is equal.

18

12 resistors are placed on the edges of a bi-pyramid. Find the equivalent resistance between the set of points shown in the figures.

19

Find the equivalent resistance between points AB for the given circuits. Resistance of each resistor is R.

20

Find the equivalent resistance between points AB for the given circuit. Resistance of each resistor is R.

21

A finite square grid, with each link of resistance r, is fitted in a zero resistance conducting circular wire. Determine the equivalent resistance between A and B.

22

In the infinite grid shown in the figure, value of each resistance is r. Find the equivalent resistance between the points A and B.

23

Find the current in each branch of the circuits shown below.

24

Find the potential of points A, B and C shown in the figure.

25

In the circuit shown, current through the 20 V cell is ?

26

In the circuit shown in figure, find the current flowing through the middle battery.

27

For the circuit shown in figure, find the current in each segment.

28

Calculate the current through each resistance in the given circuit. Assume that all the cells have no internal resistance.

29

In the circuit shown in figure, find the current in each section.

30

Find the potential difference between points A and B shown in the circuit.

31

Find the current in each resistor.

32

Find the current i shown in the fig.

33

For the circuit shown in figure, find the equivalent resistance between A and C

34

The current in a wire varies with time according to the equation is = 2 + 3t, where i is in amperes and t is in seconds. Calculate the amount of charge which passes through a cross section of the wire from t = 4 sec to t = 8 sec.

35

The current density across a cylindrical conductor of radius R varies in magnitude according to the equation

36

Find the resistance of the conductor shown in the figure.

37

The temperature coefficient of resistance of conductor varies with temperature as a ( T ) = 3T + T2. If R0 is resistance at T = 0 and RT is resistance at T, Then

38

Resistance of a resistor at temperature T oC is RT = Ro ( 1 + AT + BT2 ), where Ro is the resistance at 0 oC. The temperature coefficient of resistance at temperature T oC is

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