Magnetism PDF

# Introduction: - NS - Diamagnetic Material - Magnetic Field H=0 - Paramagnetic Material - Magnetic Field H=0 - Magnetic Field H>0 # Unit 4 Magnetism - Magnetism: phenomenon associated with magnetic fields, magnets, or the magnetic fields created by moving electric charges. - The...

# Introduction: - NS - Diamagnetic Material - Magnetic Field H=0 - Paramagnetic Material - Magnetic Field H=0 - Magnetic Field H>0 # Unit 4 Magnetism - Magnetism: phenomenon associated with magnetic fields, magnets, or the magnetic fields created by moving electric charges. - The force of magnetism can attract or repel other magnets, and change the motion of other charged particles. - Definition and Properties of Magnetic Field: The magnetic field is the region around a magnetic material or moving electric charge within which the force of magnetism acts. - Magnetic fields are represented using magnetic field lines, see figure (4.1). # Fig. (4.1) Magnetic lines of force of a bar magnet: - N - S # Some Important Properties of Magnetic Fields: - The tangent drawn to the magnetic field lines gives the direction of the magnetic field. - The closeness or density of the field lines is directly proportional to the strength of the field. - Magnetic field lines appear to emerge or start from the north pole and merge or terminate at the south pole. - Magnetic field lines never intersect with each other. - Magnetic field lines form a closed-loop. - Field lines have both direction and magnitude at any point on the field. Therefore, magnetic field lines are represented by a vector. - B = vector quantity - They denote the direction of the magnetic field. - The magnetic field is stronger at the poles because the field lines are denser near the poles. # Magnetic Flux: - Magnetic flux is defined as the number of magnetic field lines passing through a given closed surface. It provides the measurement of the total magnetic field that passes through a given surface area. - Here, the area A under consideration can be of any size and under any orientation with respect to the direction of the magnetic field. - Magnetic flux is commonly denoted using the Greek letter Phi or Phi suffix B (Ф or Фв). - The SI unit of magnetic flux is Weber (Wb). - Magnetic flux formula is given by: - Фв = B · A = B A cos θ - Where: - Фв is the magnetic flux. - B is the magnetic field. - A is the area. - θ is the angle between B and A at which the field lines pass through the given surface area. # Magnetic flux through a plane in this case: - Consider the special case of a plane of area A in a uniform field B that makes an angle θ with dA: - Фв = BA cos θ - If the magnetic field is parallel to the plane, as in Figure a, then θ = 90°, and the flux through the plane is zero. - If the field is perpendicular to the plane, as in Figure b, then θ = 0°, and the flux through the plane is BA (the maximum value). # Properties of the magnetic force on a charged particle moving in a magnetic field: - The magnitude FB of the magnetic force exerted on the particle is proportional to the charge q and to the speed v of the particle. - When a charged particle moves parallel to the magnetic field vector, the magnetic force acting on the particle is zero. - When the particle's velocity vector makes any angle θ ≠ 0 with the magnetic field, the magnetic force acts in a direction perpendicular to both v and B; that is, FB is perpendicular to the plane formed by v and B (Fig. 29.4a). - The magnetic force exerted on a positive charge is in the direction opposite the direction of the magnetic force exerted on a negative charge moving in the same direction (Fig. 29.4b). - We can summarize these observations by writing the magnetic force in the form: - FB = qv x B - FB = qvBsin θ ῆ # Figure 29.4: - The magnetic force is perpendicular to both v and B. - The magnetic forces on oppositely charged particles moving at the same velocity in a magnetic field are in opposite directions. # Right-hand rules Figure 29.5: - Point your fingers in the direction of B, with coming out of your thumb. - The magnetic force on a positive particle is in the direction you would push with your palm. - Where θ is the smaller angle between v and B. - From this expression, we see that FB is zero when v is parallel or antiparallel to B (θ = 0 or 180°). - And maximum when v is perpendicular to B (θ= 90°). - Magnetic field is expressed in SI units as a tesla (T), which is also called a weber per square meter: - T = Wb / m^2 = N / Cm/s = N / Am - A non-SI magnetic-field unit in common use, called the gauss (G), is related to the tesla through the conversion 1 T = 10^4 G. # Quick Quiz: - An electron moves in the plane of this paper toward the top of the page. A magnetic field is also in the plane of the page and directed toward the right. What is the direction of the magnetic force on the electron? - (a) toward the top of the page - (b) toward the bottom of the page - (c) toward the left edge of the page - (d) toward the right edge of the page - (e) upward out of the page - (f) downward into the page. - Determine the direction of the magnetic force on a charged particle as it enters the magnetic fields in each part as shown the figure below. - (a) Bin - (b) Bup - (c) Bright - (d) B at 45° # Magnetic Force Acting on a Current-Carrying Conductor: - The magnetic force on a segment of wire of length Lis - FB = (qva × B)nAL - The current in the wire is I= nqvaA. Therefore, - FB = IL X B - Where L is a vector that points in the direction of the current I and has a magnitude equal to the length L of the segment. # Magnetic Field of a Straight Current-Carrying Conductor: - A long, straight section of wire carrying a current I is shown in the diagram below. Because there is current present in the wire, a magnetic field is produced around the wire and is composed of closed concentric circles, as represented by the gray loops in figure (4.3). - The strength of a magnetic field, B, some distance d away from a straight wire carrying a current, I, can be found using the equation. - B = μ₀I / 2πd - Where μ₀ is a constant known as "the permeability of free space" and has the value μ₀ = 4π × 10^-7 T · m/A. - It should be noted that the distance d must be measured perpendicular to the wire. - Fig. (4.3) Magnetic Field of a Straight Current-Carrying Conductor # Quick Quiz: - A wire carries current in the plane of this paper toward the top of the page. The wire experiences a magnetic force toward the right edge of the page. The direction of the magnetic field causing this force is - (a) in the plane of the page and toward the left edge, - (b) in the plane of the page and toward the bottom edge, - (c) upward out of the page, - (d) downward into the page. # Quick Quiz: - The four wires shown in the Figure all carry the same current from point A to point B through the same magnetic field. In all four parts of the figure, the points A and B are 10 cm apart. Rank the wires according to the magnitude of the magnetic force exerted on them, from greatest to least. - (a), (b) = (c), (d)