Exam 23: Magnetic Flux and Faradays Law of Induction

FIGURE 23-7 -A bar magnet is placed with its north pole pointing toward a coil of wire that has a cross-sectional area of 0.02 m² and 6 turns, as shown in Figure 23-7(a). What is the magnitude of the induced emf in the coil of wire?

A 90.% efficient transformer supplies 3.0 Amperes at 6.0 volts. If the input voltage is 120. v, what is the input current?

In an RL series circuit connected to a dc source and a switch, the inductor gets 40% of its maximum current 1.8 s after the switch is closed at t = 0 s. What is the time constant of this circuit?

A 1.50-H inductor is connected in series with a 200-Ω resistor through a 15.0-V dc power supply and a switch. If the switch is closed at t = 0 s, what is the energy stored by the inductor 20.0 ms after the switch is closed?

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?

FIGURE 23-9 -A conducting rod with a length of 25 cm is placed on a U-shaped metal wire that has a resistance R of 8.0 Ω as shown in Figure 23-9. The wire and the rod are placed in the plane of the paper. A constant magnetic field of strength 0.40 T is applied perpendicular into the paper. An applied force moves the rod to the right with a constant speed of 6.0 m/s. What is the magnitude and direction of the induced current in the wire?

The inductance of a solenoid 16.0 cm long with a cross-sectional area of 1.00 × 10^-4 m² is 1.00 mH. How many turns of wire does this solenoid have?

FIGURE 23-1 -The three loops of wire shown in Figure 23-1 are all subject to the same uniform magnetic field that does not vary with time. Loop 1 oscillates back and forth as the bob in a pendulum, loop 2 rotates about a vertical axis, and loop 3 oscillates up and down at the end of a spring. Which loop, or loops, will have an induced emf?

A 25.0-mH inductor is connected in series to a 20.0-Ω resistor through a 15.0-V dc power supply and a switch. If the switch is closed at t = 0 s, what is the time constant of this circuit?

A coil of 40. turns and cross-sectional area 12. cm² is oriented perpendicular to a magnetic field, which varies from zero to 1.2 T in 0.02 s. What emf is induced in the coil?

The primary coil of a transformer has 600 turns and its secondary coil has 150 turns. If the ac current in the primary coil is 2 A, what is the current in its secondary coil?

FIGURE 23-2 -The two identical bar magnets in Figure 23-2 are dropped from rest along a vertical line passing through the center of the rings, as shown. The two rings are identical in every respect except that the ring on the right has a small break in it. Calling a_L and a_R the magnitude of the downward accelerations of the magnets on the left and right, respectively, you observe that

The coil of a generator is rotated twice as fast keeping all other factors constant. What happens to the value of the maximum induced emf?

A step-up transformer doubles a primary voltage 110 V (ac). What is the ratio of the number of turns in its primary coil to those in the secondary coil?

A coil with a self-inductance of 6 H has a constant current of 2 A flowing through it for 2 seconds. What is the emf induced in this coil?

An ideal transformer steps down 120. volts to 12. volts and the 2630. turn secondary supplies 12. Amperes. (a) Determine the current in the primary. (b) Determine the turns ratio. (c) What is the ratio of output power to input power?

The windings of a DC motor have a resistance of 6.0 Ω. The motor operates on 120. V AC, and when running at full speed it generates a back emf of 105. V. (a) What is the starting current of the motor? (b) What current does the motor draw when operating at full speed?

FIGURE 23-6 -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?

FIGURE 23-13 -A rectangular coil of N turns, length L = 25 cm, and width w = 15 cm, as shown in Figure 23-13, is rotating in a magnetic field of 1.6 T with a frequency of 75 Hz. If the coil develops a sinusoidal emf of maximum value 56.9 V, what is the value of N?

How would the self-inductance, L, of a coil change if you would increase its radius by a factor of two and increase its length by a factor of two?