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B = BA Cos Example 1.1 A coil consists of 200 turns of wire. Each turn is a square of side 18 cm, and a uniform magnetic field directed perpendicular to the plane of the coil is turned on. If the field changes linearly from 0 to 0.50 T in 0.80 s, what is the magnitude of the induced emf in the coil while the field is changing? Solution Since = zero cos 0 = 1 4.05 volts Example 1.2 Consider a single circular loop (or coil) with a 2.50-cm radius in a constant magnetic field of 0.625 T. Find the magnetic flux through this loop when it’s normal makes an angle of (a) 0o, (b) 30.0o, (c) 60.0o, and (d) 90.0o with the direction of the magnetic field B. Solution BA cos Br 2 cos (a) 0.625T 0.025 cos0o 1.23103 Wb 2 (b) 0.625T 0.025 cos30o 1.07 103 Wb 2 (c) 0.625T 0.025 cos60o 6.1510 4 Wb 2 (d) 0.625T 0.025 cos90o 0 2 Example 1.3 The induced emf in a single loop of wire has a magnitude of 1.48 V when the magnetic flux is changed from 0.850 T.m2 to 0.110T.m2. How much time is required for this change in flux? Solution Using equation 1.3 The induced current in a loop is in the direction that creates a magnetic field that opposes the change in magnetic flux through the area enclosed by the loop. Motors are devices into which energy is transferred by electrical transmission while energy is transferred out by work. Essentially, a motor is a generator operating in reverse. Instead of generating a current by rotating a coil, a current is supplied to the coil by a battery