https://phet.colorado.edu/sims/cheerpj/faraday/latest/faraday.html?simulation=magnets-and-electromagnetsThis is the link for no 1 and 2https://www.compadre.org/Physlets/electromagnetism/prob27_10.cfmThis is link for no 3 and 4https://www.compadre.org/Physlets/electromagnetism/illustration28_2.cfmThis link is for no 5 and 6Answers all with bold and underline questions
PhET Simulation (colorado.edu) Open the simulation. This link was also shown in the lecture, to introduce you to magnetic "B field" line. They go "out" from North, and "in" to South. Note the color-coding. 1. B field lines are Red/White when pointing north, and Red/White when pointing south. The compass needle is a small magnet itself, so functions like a "test charge" in this case a "test magnet" N: that indicates the force on it from the B field lines given by the larger bar magnet. Move the compass "over and around" the bar magnet. Is the magnetic force on the compass always shown by its alignment with the B field? Yes/No, Now click on Electromagnet at the top. The figure shows how a coil or "solenoid" with an electric current, has a magnetic B field. The electromagnet has a B field identical to a bar magnet, except it has B field lines going through its empty center. Outside, the B field is the same. It has N = 4 windings, and an electric current from the battery. The right hand end of the battery is its + end, and its is -. We follow the wires from the battery's + and - ends, and we see the electric current causing a magnetic B field. 2. Is the direction of the electric current the same as the direction of the electrons movement? Yes/Opposite. We can apply the right hand rule (RHR) number 1 to get the direction of the B field, north indicated by the red and south by the white. RHR 1 gets applied by curved fingers going along the current's direction. Apply RHR 1 and indicate the direction of the B field at the electromagnet's ends, north is to the Right/Left. Click on the Show Field Meter, at the upper right. Pull its cross hairs on top of the compass. The B field (a vector) components are shown on the meter. Is the Bx +/-? Is the By+/-? Are these consistent with the B field's indicated direction here? Yes/No? Physlet Physics by Christian and Belloni: Problem 27.10 (compadre.org) Open the simulation This is similar to Example 27-2 Measuring a Magnetic Field, in the second page of the lecture. This shows that an electric current in a B field experiences a force. Here it's a blue rod conducting the current, and the B field is shown by symbols. 3. Which direction is the B field? Left/ Right/ Down into the page/ Up out of the page. The rod has a mass, and the rod's wight is pulling it downwards (bottom of the page). Which direction of magnetic force will support the weight of the rod? Up/Down. The magnetic force equation is F = 1 1 B sin@, and since B field and current are perpendicular, @ = 90, so the equation is F = 1 1 B. We use RHR 2 to get the force direction, straight fingers on I (the first one in the equation on its right) and bent fingers on B (second one). The thumb then indicates the direction of F. Here, we have B and F directions, so this is a bit of a tough RHR 2 problem-we want to find the current I direction (to have F "up"). Doing this, we find the current direction: Right/Left. 4, Now we solve for the mass of the rod. There are two forces present, "up" from the F = 1 1 B equation, and "down" from the rod's weight Fw = m g. The indicated force in the simulation is "the force required to support the rod" so this is F = 1 1B - mg. The simulation gives us B = 2 Tesla, I = 2 Amps, and let us suppose it's an 1 = 3 m rod. It states that F = 9.43 N. Solve for m, m=. kg- Physlet Physics by Christian and Belloni: Illustration 28.2 (compadre.org) Open the simulation. Force between 2 Currents. The red wire has its B field shown. See Examples 20-10 and 20-12 in the lecture. 5. RHR 1 gives the current direction: Up out of the page/ Down into the page. Then we can use the slider below the image to increase the blue wire's current, pull it over to the right to get 2.01 A. Now the blue wire's B field "enters the picture" and combines with the red wire's B field to produce the "net B field" shown to the left. Using the field arrows surrounding the blue wire's current, give the blue wire's current direction: Up out of the page/ Down into the page. 6. We learned in the lecture that parallel currents, in the same direction, attract one another and this is shown by black arrows coming from each wire. The equation for this force is F = 2E-7 1 12 1 / d. Let's suppose the wires are 1 = 2 m long, d = 1 cm apart, and each carries 20 A of current. Calculate the force between them, F=|N
