Magnetic_Fields_and_Forces_VLab_2023 (1)

Virtual Lab: Magnetic Fields and Forces Name(s) : Date: Introduction Analogous to how electric charges produce electric fields, all moving electric charges produce magnetic fields. Similarly, just as electric charges exert electric forces on each other, the magnetic fields of moving charges exert magnetic forces on each other. An electric current flowing through a wire is a collection of moving charges and therefore has a magnetic field. This magnetic field forms closed loops around the wire, and its strength decreases with distance from the wire. The magnetic nature of current-carrying wires was discovered in 1819 by the Danish scientist Hans Christian Oersted. This demonstrated the connection between electricity and magnetism and paved the way for the modern era of electric motors and generators. The connection between electricity and magnetism can be demonstrated in the laboratory. If a magnetic compass is brought near a current-carrying wire, it is deflected due to the magnetic field of the wire. In the same way, if a current-carrying wire is placed in the magnetic field of a magnet, it will feel a force due to the interaction of its own magnetic field, and that of the external magnet. Current-carrying wires exert magnetic forces on each other. This property was first investigated by the French scientist Andre-Marie Ampere. He found that two parallel wires carrying an electric current in the same direction exert an attractive force on each other. On the other hand, if the currents in these two parallel wires flow in opposite directions, then they repel each other. The magnitude of this force (F) is given by: F = ILB sin α [ 1 ] where I is the strength of the current flowing through the wire (in amperes), L is the length of wire in the magnetic field, B is the strength of the magnetic field, and α is the angle between the wire and the magnetic field. Based on Newton’s third law, the two wires exert forces of equal magnitude, but opposite direction on each other. The strength of the magnetic field ( B ) at a distance r from a long, straight wire carrying a current I , is given by: B = μ 0 I 2 πr [ 2 ] 1

where  0 is the permeability constant: μ 0 = 1.26 × 10 − 6 T m / A From equation [2], we see that the magnetic field strength ( B ) around a current-carrying wire decreases with distance in an inverse relationship ( 1/r ). In part A of this lab, we will investigate the magnetic field around a current-carrying wire and verify equation [2]. In parts B and C of the lab, we will explore forces acting on current-carrying wires. Part A Magnetic field of a current-carrying wire In this part of the lab, we will study how the strength of the magnetic field of a current- carrying wire changes with distance. We will use a free online simulation provided by Prof. Frank McCulley at “The Physics Aviary.” You can access this simulation at this website: https://www.thephysicsaviary.com/Physics/Programs/Labs/FieldFromWire/index.html Read the instructions on the simulation start page and then click on “ Begin .” The animation uses a magnetic field sensor to measure the strength of the magnetic field ( B ) at different distances from a current-carrying wire. 1. Click on the “ Grid ” tab and move the “ Magnetic field sensor ” to a distance of 1 cm from the wire using the “ Location of Field Sensor ” arrows as shown in the figure below. Click on the “ Field Strength ” and “ Current ” tabs to display their values. Change the direction of current to conventional (right to left). Use the current value closest to 2.5 A . Click on “ Field Strength ” at the top right and record your measured magnetic field in tesla (T) in Table 1 below. Record the absolute value (ignore any negative signs). Click on “ Field ” at the top to view the closed loops of the magnetic field encircling the wire. Record the direction of the magnetic field at the top of the wire where the sensor is located. The first row has been completed as an example. You may replace this row with your own measurements. Enter the magnetic field values using “ e ” for the exponent instead of “x10^” for easier graphing in Excel. Note : one microtesla (1 μT) is 1e -6 Tor 10 -6 T. 2. Move the magnetic field sensor to a distance of 2 cm from the wire and record the magnetic field strength in row 2. Keep the current fixed at the same value (about 2.5 A). 2

3. Repeat step 2 for the different distances listed in Table 1 to complete the table. Figure 1 : Explanation of the magnetic field animation. 3