Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Fictitious force wikipedia , lookup
Centrifugal force wikipedia , lookup
Magnetohydrodynamics wikipedia , lookup
Electromagnetic field wikipedia , lookup
Force between magnets wikipedia , lookup
Electromagnet wikipedia , lookup
Faraday paradox wikipedia , lookup
Centripetal force wikipedia , lookup
PHYS219 Fall semester 2014 Lecture 11: Force on Current-Carrying Wires Dimitrios Giannios Purdue University The Lorentz Force • The Lorentz Force - the force on a charged particle moving in a magnetic field • Coulomb’s Law correctly gives the force between two point charges when they are at rest. • When the two charges are in motion, there is an extra force called the “magnetic force”. In what follows, we provide a very simple introduction to this magnetic force. The magnetic force on a charged particle in a uniform B field (from systematic experiments) a) zero velocity NO FORCE ! b) velocity parallel to B NO FORCE ! c) velocity perpendicular to B MAXIMUM FORCE It’s a cross-wise force!! Direction of magnetic force on a charged particle moving in a uniform B field http://www.conspiracyoflight.com/Lorentz/Lorentzforce.html The Lorentz Force (1892) OR (a) Focus on the plane containing v and B (b) (c) (d) Always chose the smallest angle between B and v This implies that a charge q of 1 C moving with a velocity v of 1 m/s perpendicular to a magnetic field B of 1 T experiences a force F of 1 N. What is the magnetic force on the charged particle? F B v F B v direction?? for +q charge; reverse F if q is negative Force on a current carrying wire in a B field 1. An electric current is a collection of moving charges I= ΔQ/ Δ t 2. From the equation of the force on a moving charge F = qvB sinθ q= Δ Q v=L/ Δ t F=(Δ Q)(L/ Δ t)B sinθ 3. The force on a current-carrying wire is Fon wire =I L B sin θ 4. The direction of the force is given by the right-hand rule conventional current Example =1.3 A L=1.5 m A 1.5 m long piece of wire is in a uniform magnetic field of 2 T. If the wire is carrying a current of 1.3 A, what force will it feel? =2.0 T v (or I) B F is in -x direction?? Consequence: MAGNETIC force between current-carrying wires X B V Similar Force on wire 2 Parallel currents attract Wires are electrically neutral, but still feel a force! What is the force between two parallel wires? (from experiment) Parallel Currents Attract Antiparallel Currents Repel Force on a Current Loop Equilibrium Orientation 3 A Home-Made Motor The general case line ┴ to plane of loop Example line ┴ to plane of loop A loop of wire with a 15 cm radius is placed in a uniform magnetic field of 2 T at an angle of 45o. If the wire is carrying a current of 10 A, what torque will the coil feel? Lawn mower torques – for comparison? Craftsman 37436 PRICE: $430 TORQUE: 7 lb-ft