if necessary). 14. When a magnetic field is changed from 0 T to 1.5 T, an emf of 2.5 V is created in a loop of wire with a radius of 50 cm. How fast was the magnetic field changed? (Be able to solve general equations with Faraday's law and use the induced emf in Ohm's law.) 15. A rod of length L = 10 cm slides to the right at a constant speed v = 5.0 m/s along frictionless conducting rails attached to a resistor in a uniform magnetic field B = 0.80 T pointing out of R the page as shown by the dots in the figure. If the current in the B resistor is 0.2 A, what is its resistance? (Be able to solve Faraday's law problems with motional emf and use that emf in Ohm's law). 16. When the energy stored in a solenoid is doubled, how has the magnetic field changed? (Know how to use the equation for magnetic energy stored in a magnetic field.) 17. If the frequency of a generator is doubled, what happens to the maximum voltage? (Understand and know how to use the equation for a generator.)