# UNIT – 3 MAGNETOSTATICS, ELECTROMAGNETIC FIELD THEORY Important Q/A AKTU

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Important Questions For Electromagnetic Field Theory:
*Unit-01     *Unit-02
*Unit-03    *Unit-04
*Unit-05    *Short-Q/Ans
*Question-Paper with solution 21-22 ```

## Q1. What is magnetostatic field ?

Ans.

• 1. A magnetostatic field is produced by a constant current flow (or direct current).
• 2. This current flow may be caused by conduction currents in current-carrying wires, persistent electron beam currents in vacuum tubes, or magnetization currents as in magnets.
• 3. There are two major laws governing magnetostatic fields:
• i. Biot-Savart’s law
• ii. Ampere’s circuit law.

## Q2. A single turn circle coil of 50 meters in diameter carries eurrent 28 x 104 amp. Determine the magnetic field intensity H at a point on the axis of coil and 100 meters from the coil. The relative permeability of free space surrounding the coil is unity.

Ans.  Given: Diameter 50 m, i.e, Radius, a =25 m,I = 28 x 104 amp, Distance from center (x)= 100 m, μo = 1

To Find: Hat 100 m distance.

## Q3. Derive an expression for a magnetic field intensity in solenoid having length L, N numbers of turns of wire carryingI current. While the length of solenoid is much larger then it’s radius.

Ans. 1. As the solenoid consists of circular loops, therefore the contribution to the magnetic field H at P by an element of the solenoid of length dz is

## Q4. Explain the terms magnetic scalar and vector potential.

Ans. A. Magnetic scalar potential:

3. It is noticed that if magnetic field intensity is defined as the gradient of magnetic scalar potential, then current density is zero across the region in which scalar magnetic potential is defined because the curl of the gradient of any scalar identity is zero.Thus,

B. Magnetic vector potential:

3. The characteristics of vector magnetic potential are:

i. It exists even when Vector J is present.

ii. Vector magnetic potential Vector A has applications to obtain radiation characteristics of antennas, apertures and also obtain radiation leakages from transmission line , waveguides and microwave ovens.

iii. Vector A  is used to find near and far fields of antennas.

Ans.

## Q6. State and explain the Biot-Savart’s law.

Ans. 1. Biot-Savart’s law states that the differential magnetic field intensity dH produced at point P, as shown in Fig., by the differential current element I dl is proportional to the product I dl and sine of angle (a) between the element and the line joining point P to the element and is inversely proportional to the square of the distance R between P and the element.