Physics is the natural science that studies matter,[a] its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force.[2] Physics is one of the most fundamental scientific disciplines, with its main goal being to understand how the universe behaves.[b][3][4][5] A scientist who specializes in the field of physics is called a physicist.
Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest.[6] Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the Scientific Revolution in the 17th century these natural sciences emerged as unique research endeavors in their own right.[c] Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other sciences[3] and suggest new avenues of research in these and other academic disciplines such as mathematics and philosophy.
Advances in physics often enable advances in new technologies. For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons;[3] advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus.
Astronomy is one of the oldest natural sciences. Early civilizations dating back before 3000 BCE, such as the Sumerians, ancient Egyptians, and the Indus Valley civilisation, had a predictive knowledge and a basic awareness of the motions of the Sun, Moon, and stars. The stars and planets, believed to represent gods, were often worshipped. While the explanations for the observed positions of the stars were often unscientific and lacking in evidence, these early observations laid the foundation for later astronomy, as the stars were found to traverse great circles across the sky,[6] which however did not explain the positions of the planets.
According to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy.[11] Egyptian astronomers left monuments showing knowledge of the constellations and the motions of the celestial bodies,[12] while Greek poet Homer wrote of various celestial objects in his Iliad and Odyssey; later Greek astronomers provided names, which are still used today, for most constellations visible from the Northern Hemisphere.[13]
4. Introduction
• A useful law that provides a method to
calculate the magnetic field produced by
an arbitrary current distribution.
• First discovered by Jean-Baptiste
Biot and
Félix Savart in the beginning of 19th
century
5. introduction
The Biot Savart Law is an equation
describing the magnetic field generated
by a constant electric current. It relates
the magnetic field to the magnitude,
direction, length, and proximity of the
electric current. Biot–Savart law is
consistent with both Ampere's
circuital law and Gauss's theorem
6. Definition
• According to this law the magnitude of magnatic
field due to current element is directly
proportional to ds, sign of angle, and inversaly
propotional to the square of distance between the
point p and ds.
with
the permeability of free
space.
7. Thus the total magnetic field vector B is the sum of all
of these small elements or, since they are
differentially small, it is equivalent to the integral of
dB over the current source.
Several key points to remember:
• B is a vector quantity which direction is determined by
the cross product ds x r (and is perpendicular to both ds
and r)
• The integration takes place over the entire current
source (finite or infinite)
• Since the integral is a vector integral, the expression for
B
is really three integrals, one for each component of B.
31. •When a current-carrying conductor is placed in an
external magnetic field B, the magnetic force on the
conductor is given by: F = I·(L x B).
•Consider two parallel wires of equal length carrying
a steady current:
• The two wires will exert magnetic forces on each other.
• Wire 1 will exert a magnetic force on wire 2; wire 2 will exert a magnetic
force on wire 1.
32. • The wires are separated by distance a and carry currents I1 and I2
in the same direction.
• Wire 2, carrying current I2, sets up a magnetic field B2 at the
position of wire 1.
- The direction of the magnetic field B2 is perpendicular to the
wire.
- F1 = F2 on 1 = I1·(L x B2)
- Angle q between L and B2
is 90.
34. • F1 = F2 on 1 = I1·(L x B2) = I1·L·B2·sin q
F1 = F2 on 1 = I1·L·B2
• Biot-Savart law for the magnetic field B2:
• Substituting:
a
π
2
I
μ
B 2
o
2
a
π
2
I
I
μ
L
F
F
a
π
2
I
μ
L
I
B
L
I
F
F
2
1
o
1
on
2
1
2
o
1
2
1
1
on
2
1
35. •Rewriting in terms of the force per unit length:
•The direction of F1 is downward and is
determined using the right hand rule (fingers of
right hand in direction of current I; palm facing
in the direction of B; thumb points down in the
direction of F1)
•The magnetic force that wire 1 exerts on wire 2
(F1 on 2) is equal in magnitude to and opposite in
direction to F1 (F2 on 1).
a
π
2
I
I
μ
L
F 2
1
o
36. •Wire 1 and wire 2 will attract each other.
•When the currents are in opposite directions, the
magnetic forces again equal in magnitude but
are opposite in direction and the wires repel
each other.
•Conclusions: parallel conductors carrying
currents in the same direction attract each other;
parallel conductors carrying currents in opposite
directions repel each other.
38. Force between two parallel current-
carrying straight wires
1. Parallel wires with current flowing in the same direction, attract
each other.
2. Parallel wires with current flowing in the opposite direction, repel
each other.
39. •The force between two parallel wires each
carrying a current is used to define the
ampere (A):
•If two long, parallel wires 1 m apart carry
the same current I and the force per unit
length on each wire is 2 x 10-7 N/m, then
the current is defined to be 1 A.
•If I1 = I2 = 1 A and a = 1 m, the numerical
value of 2 x 10-7 N/m is obtained from:
a
π
2
I
I
μ
L
F 2
1
o
40. •The unit of charge, the coulomb, can be
defined in terms of the ampere:
•a conductor carries a steady current of
1 A, then the quantity of charge that
flows through a cross-section of the
conductor in 1 s is 1 C.
