Moving charges and Magnetism Flashcards
What is biot- savart law
The magnitude of magnetic field produced due to a small current element is:
i)directly proportional to current I flowing through the conductor
ii)directly proportional to the length dl of the current element
In) directly proportional to the sina where a is the angle b/w the point and the current element
Iv) inversely proportional to the square of the distance of the point and current element.
dB = k I dl sina/r2
k=uo/4 π
similartieis between coloumb law and biot savart law
(i) Both are long range, since both depend inversely on the square of
distance from the source to the point of interest. The principle of
superposition applies to both fields. [In this connection, note that
the magnetic field is linear in the source I dl just as the electrostatic
field is linear in its source: the electric charge.]
(ii) The electrostatic field is produced by a scalar source, namely, the electric
charge. The magnetic field is produced by a vector source I dl.
(iii) The electrostatic field is along the displacement vector joining the
source and the field point. The magnetic field is perpendicular to the
plane containing the displacement vector rand the current element I dl.
(iv) There is an angle dependence in the Biot-Savart law which is not
present in the electrostatic case. In Fig. 4.7, the magnetic field at any
point in the direction of dl (the dashed line) is zero. Along this line,
q = 0, sin q = 0 and from Eq. [4.11(a)], |dB| = 0.
What is permeability of free space ?
It depends on the medium between the current element and the point
state ampere’s circuital law
The line integral of magnetic field B around a closed loop is equal to uo times the total current passing through this closed loop.
what is the sign of current for amperes circuital law
Apply right hand rule. Curl your fingers inthe direction of the loop taken. The direction in which the thumb points is +ve.
describe the features of magnetic field due to a straight current carrying wires
i) The magnetic field due to a straight current carrying wire is same at all points that are a distance r from the wire. Hence it is said to follow cylindrical symmetry ( The value of field depends only one coordinate).
ii) The field direction at any point on this circle is tangential to it.
Thus, the lines of constant magnitude of magnetic field form
concentric circles
iiii)the wire is
infinite, the field due to it at a non-zero distance is not infinite. It
tends to blow up only when we come very close to the wire. The
field is directly proportional to the current and inversely
proportional to the distance from the (infinitely long) current source
iv) direction of field can be deduced by right hand thumb rule
what is a solenoid
It consists of a long wire
wound in the form of a helix where the neighbouring turns are closely
spaced. So each turn can be regarded as a circular loop.Enamelled wires
are used for winding so that turns are insulated from each other
what is a long solenoid
By long solenoid we mean that the
solenoid’s length is large compared to its radius.
what is the magnetic field of a solenoid
Inside the solenoid the field is unform and along the axis of the solenoid.
Outside the solenoid, the field is approaching 0 and hence can be considered 0.
