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NOTES 36A - Topic 5 - Electricity & Magnetism - ------------------------------------------------------------------------------------------------ 6 .3.3 Force on I-wire in B • Use Modified RHR (+ charges) and Modified LHR (- charges) to determine
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NOTES 36A - Topic 5 - Electricity & Magnetism ------------------------------------------------------------------------------------------------- 6.3.3 Force on I-wire in B • Use Modified RHR (+ charges) and Modified LHR (- charges) to determine direction of force exerted on current-carrying wire in B and moving charged particles in B: With hand flat and thumb extended... when thumb points in direction of current (moving charges), and fingers point in direction of B , bent index finger points in direction of resultant force;
6.3.4 Force on Moving q in B • Use Modified RHR to determine direction of force exerted on moving + charged particles in B: With right hand flat and thumb extended... when thumb points in direction of moving + charge, and fingers point in direction of B , bent index finger points in direction of resultant force; • Use Modified LHR to determine direction of force exerted on moving - charged particles in B (same as above, but left hand for electrons); B S F + F N -
6.3.5 Magnetic Forces on I and q and Magnetic Field Strength Problems • The amount of force exerted on a current-carrying wire in a magnetic field is given by: FB = I L B sin θ, where I is current (A), L is length of wire in B (m), B is strength of magnetic field (T), and θ is the angle the wire makes with B (if θ = 0, wire is parallel to field lines and FB = 0); • The amount of force exerted on a moving charged particle in a magnetic field is given by: FB = q v B sin θ, where q is charge (C), v is velocity of particle (m s-1), B is strength of magnetic field (T), and θ is the angle the particle makes with B (if θ = 0, particle moves parallel to field lines and FB = 0);
• To determine the strength of a magnetic field (B)... If ...FB = I L B , then B = FB / I L = N / A m = N A-1 m-1 ; And if... FB = q v B , then... B = FB / q v = N / (C) (ms-1) = N / A m = N A-1 m-1 ; 1.0 N A-1 m-1 = 1.0 Tesla = 1.0 T ;
Sample Problem 1: For a 1.0 m wire carrying a 1.0 A current and experiencing a magnetic force of 1.0 N, calculate the strength of the magnetic field (show solution in NB): Given: Unknown: Equation: ...The strength of the magnetic field must be 1.0 Tesla, or 1.0 T; • 1.0 T is a very large unit; Bearth = 5 x 10-5 T; • 1.0 T = 1.0 x 104 Gauss (G) ; • Bearth = 5 x 10-5 T = 0.5 G;
• Sample Problem 2: (show solution in NB): 1. What is the force exerted on an electron moving perpendicularly at 1.0 x 105 m s-1 through a magnetic field of 50. G? Given: Unknown: Equation:
Sample Problem 3: What magnetic field strength (aka magnetic flux density) would produce a 0.050 N force on 3.5 m of straight wire carrying 1.5 A of current that is at an angle of 45o to magnetic field lines? Given: Unknown: Equation: