Physics Magnetic Effect Of Electric Current
Oersted’s Experiment
Oersted’s experiment was a groundbreaking experiment conducted by the Danish physicist Hans Christian Ørsted in 1820. It demonstrated the connection between electricity and magnetism, revolutionizing our understanding of electromagnetism.
Background
Prior to Oersted’s experiment, electricity and magnetism were considered separate phenomena. Electricity was associated with the flow of electric charges, while magnetism was attributed to the attraction and repulsion of magnets.
The Experiment
In his experiment, Ørsted placed a wire carrying an electric current near a compass needle. He observed that the needle deflected from its original northsouth orientation when the current was turned on. This deflection indicated that the electric current created a magnetic field around the wire.
Key Observations
The following key observations were made during Oersted’s experiment:
 The direction of the compass needle deflection depended on the direction of the electric current.
 The strength of the magnetic field increased with the strength of the electric current.
 The magnetic field was strongest near the wire and decreased with distance from the wire.
Significance
Oersted’s experiment provided experimental evidence for the relationship between electricity and magnetism. It laid the foundation for the field of electromagnetism, which has had a profound impact on various areas of science and technology.
Some of the significant implications of Oersted’s experiment include:
 The development of electric motors, which convert electrical energy into mechanical energy.
 The invention of generators, which convert mechanical energy into electrical energy.
 The advancement of telegraphy, allowing for longdistance communication using electrical signals.
 The basis for understanding electromagnetic waves, such as radio waves, microwaves, and light.
Oersted’s experiment was a pivotal moment in the history of physics. It established the connection between electricity and magnetism, opening up new avenues for scientific exploration and technological innovation. The principles discovered through this experiment continue to shape our understanding of electromagnetism and its applications in various fields.
Lorentz Force
The Lorentz force is a fundamental force in electromagnetism that describes the interaction between moving electric charges and magnetic fields. It is named after the Dutch physicist Hendrik Lorentz, who developed the theory in the late 19th century.
Key Concepts
 Electric Charge: An electric charge is a fundamental property of matter that can be either positive or negative. Electric charges interact with each other through the electromagnetic force.
 Magnetic Field: A magnetic field is a region of space around a magnet or electric current where the magnetic force can be detected. Magnetic fields are created by moving electric charges.
 Lorentz Force: The Lorentz force is the force exerted on a moving electric charge in the presence of a magnetic field. The force is proportional to the charge of the particle, the strength of the magnetic field, and the velocity of the particle.
Mathematical Formulation
The Lorentz force is given by the following equation:
$$\mathbf{F} = q(\mathbf{E} + \mathbf{v} \times \mathbf{B})$$
where:
 F is the Lorentz force vector
 q is the electric charge of the particle
 E is the electric field vector
 v is the velocity vector of the particle
 B is the magnetic field vector
The first term on the right side of the equation represents the electric force, which is the force exerted on a charged particle by an electric field. The second term represents the magnetic force, which is the force exerted on a moving charged particle by a magnetic field.
The Lorentz force is a fundamental force in electromagnetism that has a wide range of applications in various fields of science and technology. It is a powerful tool for understanding the interactions between electric charges and magnetic fields.
BiotSavart’s Law
BiotSavart’s law is a fundamental equation in electromagnetism that describes the magnetic field generated by a currentcarrying wire. It provides a mathematical relationship between the electric current flowing through a wire and the magnetic field it creates at a given point in space.
Key Concepts:

Magnetic Field (B): The magnetic field is a vector quantity that describes the strength and direction of the magnetic force experienced by moving electric charges. It is measured in teslas (T).

CurrentCarrying Wire: A wire carrying an electric current generates a magnetic field around it. The strength of the magnetic field depends on the magnitude of the current and the geometry of the wire.

BiotSavart’s Law: This law provides a formula to calculate the magnetic field at a point due to a currentcarrying wire. It states that the magnetic field is directly proportional to the current, the length of the wire segment, and inversely proportional to the square of the distance from the wire.
Mathematical Formula:
The mathematical expression for BiotSavart’s law is given by:
$$ \overrightarrow{dB} = \frac{\mu_0}{4\pi} \frac{I \overrightarrow{dl} \times \hat{r}}{r^2} $$
Where:
 $\overrightarrow{dB}$ is the differential magnetic field vector at the observation point due to a small segment of the currentcarrying wire.
 $\mu_0$ is the permeability of free space, a constant equal to $4\pi \times 10^{7} \text{ T}\cdot\text{m/A}$.
 $I$ is the magnitude of the current flowing through the wire.
 $\overrightarrow{dl}$ is a vector representing the length and direction of a small segment of the wire.
 $\hat{r}$ is a unit vector pointing from the current element to the observation point.
 $r$ is the distance between the current element and the observation point.
BiotSavart’s law is a fundamental principle in electromagnetism that describes the relationship between electric currents and the magnetic fields they produce. It provides a mathematical framework for calculating the magnetic field at any point in space due to a currentcarrying wire. This law has numerous applications in various fields, including electrical engineering, physics, and material science.
Magnetic Field Due to a Straight CurrentCarrying Conductor
BiotSavart Law
The magnetic field due to a straight currentcarrying conductor can be calculated using the BiotSavart law. This law states that the magnetic field at a point due to a currentcarrying element is directly proportional to the current, the length of the element, and inversely proportional to the square of the distance from the element to the point.
Formula for Magnetic Field
The formula for the magnetic field due to a straight currentcarrying conductor is given by:
$$ \overrightarrow{B} = \frac{\mu_0}{4\pi} \frac{2I}{d} \sin\theta \hat{n} $$
Where:
 $ \overrightarrow{B} $ is the magnetic field vector
 $ \mu_0 $ is the permeability of free space $ (4\pi \times 10^{7} \text{ T}\cdot\text{m/A}) $
 $ I $ is the current flowing through the conductor
 $ d $ is the distance from the conductor to the point where the magnetic field is being calculated
 $ \theta $ is the angle between the conductor and the line connecting the conductor to the point where the magnetic field is being calculated
 $ \hat{n} $ is a unit vector perpendicular to both the conductor and the line connecting the conductor to the point where the magnetic field is being calculated
Direction of Magnetic Field
The direction of the magnetic field due to a straight currentcarrying conductor can be determined using the righthand rule. To use the righthand rule, point your right thumb in the direction of the current flow. Then, curl your fingers around the conductor. Your fingers will point in the direction of the magnetic field.
Magnetic Field Due to Circular Current Loop
A circular current loop is a wire bent into a circle and carrying a current. It creates a magnetic field in the space around it. The magnetic field of a circular current loop is similar to that of a bar magnet, with a north pole and a south pole.
BiotSavart Law
The magnetic field due to a currentcarrying wire can be calculated using the BiotSavart law. This law states that the magnetic field at a point is proportional to the current flowing through the wire and inversely proportional to the square of the distance from the wire.
For a circular current loop, the BiotSavart law can be used to calculate the magnetic field at a point on the axis of the loop. The magnetic field at a point on the axis of the loop is given by:
$$B = \frac{\mu_0 I}{4\pi R}\left(\frac{2\pi R^2}{(R^2 + z^2)^{3/2}}\right)$$
where:
 $B$ is the magnetic field in teslas (T)
 $\mu_0$ is the permeability of free space $(\mu_0 = 4\pi \times 10^{7} \text{ T}\cdot\text{m/A})$
 $I$ is the current in the loop in amperes (A)
 $R$ is the radius of the loop in meters (m)
 $z$ is the distance from the center of the loop to the point on the axis in meters (m)
Magnetic Field Lines
The magnetic field lines of a circular current loop are concentric circles. The magnetic field lines are closer together near the loop and farther apart farther from the loop. The direction of the magnetic field lines is given by the righthand rule.
The magnetic field of a circular current loop is similar to that of a bar magnet. The magnetic field of a circular current loop can be calculated using the BiotSavart law. Circular current loops are used in a variety of applications, including electromagnets, motors, generators, and transformers.
Ampere’s Law
Ampere’s law is a law of electromagnetism that relates the magnetic field around a currentcarrying wire to the electric current passing through the wire. It was discovered by AndréMarie Ampère in 1820.
Mathematical Form of Ampere’s Law
The mathematical form of Ampere’s law is:
$$\oint\overrightarrow{B}\cdot d\overrightarrow{l}=\mu_0I$$
Where:
 $\overrightarrow{B}$ is the magnetic field vector
 $d\overrightarrow{l}$ is a differential length vector along a closed loop
 $\mu_0$ is the permeability of free space
 $I$ is the current passing through the loop
Explanation of Ampere’s Law
Ampere’s law states that the magnetic field around a currentcarrying wire is proportional to the current passing through the wire. The direction of the magnetic field is given by the righthand rule.
To use the righthand rule, point your right thumb in the direction of the current. Your fingers will then curl in the direction of the magnetic field.
Applications of Ampere’s Law
Ampere’s law has a number of applications, including:
 Calculating the magnetic field around a currentcarrying wire
 Designing electromagnets
 Determining the force between two currentcarrying wires
Ampere’s law is a fundamental law of electromagnetism that has a wide range of applications. It is a powerful tool for understanding and predicting the behavior of magnetic fields.
Righthand Thumb Rule or Maxwell’s Corkscrew Rule
The righthand thumb rule, also known as Maxwell’s corkscrew rule, is a mnemonic used to determine the direction of the magnetic field around a currentcarrying wire. It is a simple and effective way to visualize and understand the magnetic field created by electric currents.
How to Use the Righthand Thumb Rule
To use the righthand thumb rule, follow these steps:
 Point your right thumb in the direction of the conventional current flow (from positive to negative).
 Curl your fingers around the wire in the direction of your thumb.
 The direction in which your fingers curl indicates the direction of the magnetic field lines around the wire.
Example
Consider a wire carrying a current from left to right. To determine the direction of the magnetic field around the wire, follow these steps:
 Point your right thumb in the direction of the current flow (from left to right).
 Curl your fingers around the wire in the direction of your thumb.
 Your fingers will curl in a clockwise direction, indicating that the magnetic field lines around the wire form concentric circles with the wire at the center.
Applications of the Righthand Thumb Rule
The righthand thumb rule is a useful tool for understanding and visualizing magnetic fields in a variety of situations, including:
 Determining the direction of the magnetic field around a solenoid.
 Finding the polarity of an electromagnet.
 Predicting the direction of the force exerted on a currentcarrying wire in a magnetic field.
 Designing and building electric motors and generators.
The righthand thumb rule is a simple but powerful tool for understanding and visualizing magnetic fields. It is a fundamental concept in electromagnetism and has numerous applications in electrical engineering and physics.
Magnetic Effect of Electric Current Solved Examples
Example 1: A Long Straight Wire
A long straight wire carries a current of 10 A. What is the magnetic field at a point 10 cm from the wire?
Solution:
We can use the formula for the magnetic field of a long straight wire:
$$B = \frac{\mu_0 I}{2\pi d}$$
where:
 $B$ is the magnetic field in teslas (T)
 mu_0 is the permeability of free space $mu_0 = 4\pi \times 10^{7} \text{ T.m/A}$
 $I$ is the current in amperes (A)
 $d$ is the distance from the wire in meters (m)
Substituting the given values into the formula, we get:
$$B = \frac{(4\pi \times 10^{7} \text{ T$\cdot$m/A})(10 \text{ A})}{2\pi (0.1 \text{ m})}$$
$$B = 2 \times 10^{6} \text{ T}$$
Therefore, the magnetic field at a point 10 cm from the wire is $2 \times 10^{6} \text{ T}$.
Example 2: A Circular Loop of Wire
A circular loop of wire has a radius of 5 cm and carries a current of 2 A. What is the magnetic field at the center of the loop?
Solution:
We can use the formula for the magnetic field at the center of a circular loop of wire:
$$B = \frac{\mu_0 I}{2R}$$
where:
 $B$ is the magnetic field in teslas (T)
 $\mu_0$ is the permeability of free space $mu_0 = 4\pi \times 10^{7} \text{ Tm/A}$
 $I$ is the current in amperes (A)
 $R$ is the radius of the loop in meters (m)
Substituting the given values into the formula, we get:
$$B = \frac{(4\pi \times 10^{7} \text{ T$\cdot$m/A})(2 \text{ A})}{2(0.05 \text{ m})}$$
$$B = 4 \times 10^{6} \text{ T}$$
Therefore, the magnetic field at the center of the loop is $4 \times 10^{6} \text{ T}$.
Example 3: A Solenoid
A solenoid is a long, cylindrical coil of wire. When a current is passed through the solenoid, it creates a magnetic field inside the coil. The magnetic field inside a solenoid is given by the formula:
$$B = \mu_0 nI$$
where:
 $B$ is the magnetic field in teslas (T)
 mu_0 is the permeability of free space $mu_0 = 4\pi \times 10^{7} \text{ T m/A}$
 $n$ is the number of turns per meter of the solenoid
 $I$ is the current in amperes (A)
A solenoid has 1000 turns per meter and carries a current of 5 A. What is the magnetic field inside the solenoid?
Solution:
Substituting the given values into the formula, we get:
$$B = (4\pi \times 10^{7} \text{ T$\cdot$m/A})(1000 \text{ turns/m})(5 \text{ A})$$
$$B = 2 \times 10^{3} \text{ T}$$
Therefore, the magnetic field inside the solenoid is $2 \times 10^{3} \text{ T}$.
Magnetic Effect of Electric Current FAQs
What is the magnetic effect of electric current?
The magnetic effect of electric current refers to the phenomenon in which an electric current flowing through a conductor creates a magnetic field around it. This magnetic field exerts a force on moving electric charges, such as electrons, and can induce magnetism in certain materials.
What is the relationship between electric current and magnetic field?
The relationship between electric current and magnetic field is described by Ampère’s law, which states that the magnetic field around a currentcarrying conductor is proportional to the magnitude of the current and inversely proportional to the distance from the conductor. The direction of the magnetic field is determined by the righthand rule.
What is the righthand rule?
The righthand rule is a mnemonic used to determine the direction of the magnetic field around a currentcarrying conductor. According to the righthand rule, if you point your right thumb in the direction of the current flow, your fingers will curl in the direction of the magnetic field lines.
What is an electromagnet?
An electromagnet is a device that uses electric current to create a magnetic field. It consists of a coil of wire wrapped around a ferromagnetic core, such as iron or steel. When an electric current flows through the coil, it generates a magnetic field that magnetizes the core. The strength of the magnetic field can be controlled by varying the amount of current flowing through the coil.
What are some applications of the magnetic effect of electric current?
The magnetic effect of electric current has numerous applications in various fields, including:
 Electric motors: Convert electrical energy into mechanical energy by utilizing the interaction between magnetic fields and currentcarrying conductors.
 Generators: Convert mechanical energy into electrical energy by exploiting the principle of electromagnetic induction.
 Transformers: Transfer electrical energy from one circuit to another through electromagnetic induction.
 Magnetic resonance imaging (MRI): Utilizes strong magnetic fields and radio waves to produce detailed images of the inside of the body for medical diagnostics.
 Magnetic levitation (maglev) trains: Use electromagnetic forces to levitate and propel trains, allowing for highspeed transportation.
 Magnetic compasses: Employ the Earth’s magnetic field and a magnetized needle to indicate direction.
 Magnetic recording: Used in devices such as hard disk drives and magnetic tapes to store and retrieve data.
Conclusion
The magnetic effect of electric current is a fundamental phenomenon that has revolutionized various technological advancements. By understanding the relationship between electric current and magnetic fields, scientists and engineers have been able to harness this effect for practical applications in diverse fields, from energy conversion to medical imaging and transportation.