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AP Physics III.D. Magnetostatics. 21.1 Magnetic Fields. The prized lodestone. Force of one magnet on another. Magnetic field as plainly demonstrated by iron filings and compasses. The Earth’s magnetic field (a source of some confusion). 21.2 The Force of a Magnetic Field on a Moving Charge.
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AP Physics III.D Magnetostatics
Magnetic field as plainly demonstrated by iron filings and compasses.
A magnetic field exerts a force on a charged particle when . . . • The charge is moving • The velocity of the moving charge has a component that is perpendicular to the direction of the field
Consider . . . 1) a magnetic field and the charge moving parallel or antiparallel to the field
2) The charge moving at 90º to the direction of the field (time for Right Hand Rule Number 1)
3) The charge moving between 0º and 180º to the direction of the field
Ex. A proton moves with a speed of 1.0 EE 5 m/s through the Earth’s magnetic field where the value at a particular location is 55 micro-Teslas. When the proton moves eastward, the magnetic force acting on it is a maximum and when it moves northward the magnetic force is zero. What is the strength of the magnetic force and the direction of the field?
Ex. A electron moves at 8.0 EE 6 m/s along the x-axis. It enters a region where there is a magnetic field of 2.5 T directed at an angle of 60.0º with the x-axis and in the x-y plane. Find the initial force and acceleration of the electron. What is the direction of the magnetic force on the electron?
p. 661: 1 – 4, 9; p. 337: 11; p. 339: 38 2. Fa = 5.7 EE -5 N (into page), Fb = 1.1 EE -4 N (into page), Fc = 5.7 EE -5 N (into page) • 1/3 38. 250 N
Work done on a charged particle moving through a electric and magnetic fields
A for a handy formula which I never remember and is not a “boxer” but one you can easily derive.
Ex. (in your book) A proton released from rest next to the positive plate of a capacitor, accelerates towards a hole in the negative plate. The potential difference between the plates is 2100 V. After passing through the hole, the proton enters a magnetic field of 0.10 T (out of the page). Find the velocity of the proton as it passes through the hole and the radius of the circular path it makes in the magnetic field.
p. 662: 10-12, 15, 20, 22, 25 • a) 2.89 EE 16 m/s2 b) 0.026 T • Find force from each field, use Pyth.Th. to find net force (0.011 N) • 6.82 EE 5 C/kg 22. 484
Ex. A rectangular loop of wire hangs vertically in a magnetic field directed out of the page. The length of the wire (ab) is 10.0 cm. The loop hangs from a balance that measures a downward force of 3.48 EE –2 N when the wire carries a current of 0.245 A. What is the magnitude of the magnetic field?
Electromagnetism – the linking of the motion of electric charges with the creation of a magnetic field
Formula for a magnetic field produced by a current carrying wire.
Ex. (in your book) The current through a wire is 3.0 A. A charge of 6.5 µC is moving parallel to a wire at a distance of 0.050 m with a velocity of 280 m/s. Find the magnitude and direction of the force on the moving charge by the current.
90B2 a) 20 000 V/m, direction? • 3.5 EE 15 m/s2, towards ? • 4.9 EE -3 m • Yirz • 6.7 EE -4 T, direction?
91B2 • i. use cons. of E ii. b) i. and ii. Yerz c)