Magnetic Force (strength) - Assignment 21

Unravel the mysteries of magnetic force! Learn to calculate force on wires and particles using F=ILB and F=qvB.

Magnetism In 1820, Orsted demonstrated the connected between electricity and magnetism.What is the only thing you really need to understand magnetism : your right hand.Only certain materials, especially those containing iron, can be magnets.Magnetic field lines point from the north pole to the south pole, like how electric field lines point from the positive to the negative charge.A fundamental principle of electromagnetism is that an electric current produces a magneticfield.When a current runs through a wire, a magnetic field runs aroundit. (this should have been one of our drawings from last week)The first right hand rule tells you that the direction your fingers are pointing when curled around a wire (with the thumb of your right hand pointing in the direction of the electric current) is the direction of the magnetic field lines.The direction of the force from a magnetic field on a current running through a wire will be perpendicularto both the magnetic field and the current.The second right hand rule lets you keep track of 3 directions: the direction of the magnetic field, the current, and the force. Point your right armin the direction of the current, then point your fingers so they are perpendicular to your palm – this represents the direction of the magnetic field. Your thumb, perpendicular to your fingers, is the direction of the force on the wire. (I am supper bummed to not be doing this is class. It definitely takes some practice to get used to these conventions)The equation for finding the magnetic force on a wire is F=ILBsin(theta) where:F = magnetic forcemeasured in NewtonsI = current measured in AmperesL = lengthof wire measured in metersB = magnetic fieldmeasured in TeslaIf the current is parallel to the magnetic field lines, there won’t be any force on the wire at all.Currents are made up of moving electric charges, so a magnetic field will exert a force on single electric charges that pass through it. This is the concept that explains why Earth’s magnetic field protects us from charged particles from the sun.The equation for finding the magnetic force on a single charged particle is F=qvBsin(theta) where:F = magnetic forcemeasured in Newtonsq= chargemeasured in Coulombsv = velocityof charged particle measured in meters = magnetic fieldmeasured in TeslaFor the third right hand rule, if the charged particle is positive, then your thumb is point in the direction of the force. If the charge is negative, then your thumb is pointing in the direction opposite the force.Your arm is the direction of the particle velocity and your fingers, which are perpendicular to your thumb and arm, are the direction of the magnetic field. Strength of Magnetic Force. As was mentioned in the video, there are two equations to calculate the magnetic force.One of the equations is for the magnetic force created by a current carrying wire. If the word problem says current or wire, you know you will be using the equation F = ILB (for this class, we are going to assume that our field, current, and force are all perpendicular to each other and we will drop the sin(theta) from the original equation)rearranged for current I = F rearranged for length L = F rearranged for field B = F other equation is for the magnetic force created by a charged particle. If the word problem says velocity or particle, you know you will be using the equation F =qvB (we drop the sin(theta) for this one too).rearranged for charge q = F rearranged for velocity v = F rearranged for field B = F A fax machine requires 1.4 A of current to pass through a 2 m cable in order to work. If the magnetic field perpendicular to the cable is 3.6 × 10–4 T, what is the magnetic force exerted on the cable? 1) list the variables (with units) 2) pick the equation 3) plug and solve. Suppose a wire is placed perpendicular to a uniform magnetic field of 4.6 × 10–4 T. A magnetic force of 2.9 × 10–3 N is exerted on the wire. If the current in the wire is 10.0 A, how long is the wire? 1) list the variables (with units) 2) pick the equation 3) plug and solve. A 12 m wire carrying a current of 12 A is placed at right angles to a uniform magnetic field. A magnetic force of 7.3 × 10–2 N acts on this wire. What is the magnitude of the magnetic field? 1) list the variables (with units) 2) pick the equation 3) plug and solve. A printer is connected to a 1.0 m cable. If the magnetic force is 9.1 × 10–5 N, and the magnetic field is 1.3 × 10–4 T, how much current passes through the wire? 1) list the variables (with units) 2) pick the equation 3) plug and solve. A proton (q = 1.6 × 10–19 C) moves at right angles to a uniform magnetic field of 0.8 T. If the speed of the proton is 3.0 × 107 m what is the magnetic force exerted on the proton? 1) list the variables (with units) 2) pick the equation 3) plug and solve. An electron (q = 1.6 × 10–19 C) in a cathode ray tube (found in many televisions) moving at a speed of 1.2 × 106 m has a magnetic force of 1.2 × 10–17 N acting on it. What is the magnitude of the magnetic field perpendicular to the electron’s path? 1) list the variables (with units) 2) pick the equation 3) plug and solve. An electron (q = 1.6 × 10–19 C) moves perpendicular to a sunspot at a speed of 7.8 × 106 m A magnetic force of 3.7 × 10–13 N is exerted on the electron. What is the magnitude of the magnetic field emitted by the sunspot? 1) list the variables (with units) 2) pick the equation 3) plug and solve. The magnetic field in the Crab Nebula is about 1 × 10–8 T. If an electron moving perpendicular to this field is affected by a magnetic force of 3.2 × 10–22 N, what is the electron’s speed? The charge of an electron is 1.6 × 10–19 C. 1) list the variables (with units) 2) pick the equation 3) plug and solve.