Exam 29: Electromagnetic Induction and Faradays Law

A loop of radius r = 3 cm is placed parallel to the xy-plane in a uniform magnetic field = ( 0.75 T) . The resistance of the loop is R = 18 Ω. Starting at t = 0, the magnitude of the field decreases uniformly to B = 0 in 0.15 seconds. What is the magnitude of the electric current produced in the loop during that time?

The windings of a DC motor have a resistance of 6.00 Ω. The motor operates on 120 V AC, and when running at full speed it generates a back emf of 105 V. What is the starting current of the motor?

An airplane is flying horizontally in a region where the earth's magnetic field is 5.2 × 10^-5 T downward. If the speed of the plane is 200 m/s and the wing tips are 65 m apart, what is the potential difference between the wing tips?

In a transformer, how many turns are necessary in a 110-V primary if the 24-V secondary has 100 turns?

A coil is rotating at constant speed within a uniform magnetic field. What can be said about the magnitude of the emf induced in the coil?

An ac generator consists of a coil with 40 turns of wire, each with an area of 0.06 m². The coil rotates in a uniform magnetic field B = 0.4 T at a constant frequency of 55Hz. What is the maximum induced emf?

An emf is induced in a wire by changing the current in that wire.

The negative sign in the Faraday's equation for electromagnetic induction is related to the direction of the induced emf.

A generator produces 60 A of current at 120 V. The voltage is usually stepped up to 4500 V by a transformer and transmitted through a power line of total resistance 1.0 Ω. Find the number of turns in the secondary if the primary has 200 turns.

FIGURE 29-4 -Fig. 29-4 shows the time evolution of a uniform magnetic field. Four particular instants labeled t_A to t_D are also identified on the graph. The field passes through a circular coil whose normal is parallel to the direction of the field. At what time does the current induced in the coil have the largest value?

In a transformer, the power input

A circular loop of wire is in the plane of the paper. The north pole of a bar magnet is being moved toward the center of the loop from a position in front of the paper. The direction of the induced current in the loop

FIGURE 29-2 -The wire in Fig. 29-2 carries a current I that is increasing with time at a constant rate. The induced emf in each of the loops is such that

FIGURE 29-13 -A power transmission line 50 km long has a total resistance of 0.60 Ω. A generator produces 100 V at 70 A. In order to reduce energy loss due to heating of the transmission line, the voltage is stepped up with a transformer with a turns ratio of 100:1. (a) What percentage of the original energy would be lost if the transformer were not used? (b) What percentage of the original energy is lost when the transformer is used?

If the number of turns on the secondary coil of a transformer are less than those on the primary, the result is a

A transformer changes the 10,000 V power line to 120 V. If the primary coil contains 750 turns, how many turns are on the secondary?

The area of a rectangular loop of wire is 3.6 × 10^-3 m². The loop is placed in a magnetic field that changes from 0.20 T to 1.4 T in 1.6 s. The plane of the loop is perpendicular to the direction of the magnetic field. What is the magnitude of the induced emf in that loop?

FIGURE 29-13 -The windings of a motor have a resistance of 4.0 Ω. The counter emf of this motor when connected to a 120-V line and running at full speed is 104 V. (a) What is the start up current of this motor? (b) What is the current in the motor when running at full speed?

A conducting loop in the form of a circle is placed perpendicular to a magnetic field of 0.50 T. If the area of the loop increases at a rate of 3.0 × 10^-3 m² /s, what is the induced emf in the loop?

The primary coil of a transformer has 100 turns and its secondary coil has 400 turns. If the ac voltage applied to the primary coil is 120 V, what voltage is present in its secondary coil?