Exam 30: Electromagnetic Induction

A bar magnet is held vertically with its upper end a little bit below the center of a horizontal metal ring.The upper end of the magnet is its north pole,as shown in the figure.The bar magnet is now dropped.An observer views the ring from above its center.To this observer,how will the induced current in the ring behave as the magnet falls?

What resistance should be added in series with a 3.0-H inductor to complete an LR circuit with a time constant of ?

An LC circuit consists of a 3.4-µF capacitor and a coil with a self-inductance 0.080 H and no appreciable resistance.At t = 0 the capacitor has a charge of 5.4 µC and the current in the inductor is zero. (a)How long after t = 0 will the current in the circuit be maximum? (b)What will be this maximum current?

A 50-cm wire placed in an east-west direction is moved horizontally to the north with a speed of 2.0 m/s.The horizontal component of the earth's magnetic field at that location is 25 μT toward the north and the vertical component is 50μT downward.What is the emf induced between the ends of the wire?

In the figure,two parallel wires carry currents of magnitude I in opposite directions.A rectangular loop is midway between the wires.The current I is decreasing with time.The induced current through the resistor R is

In the figure,the inner loop carries a clockwise current I that is increasing.The resistor R is in the outer loop and both loops are in the same plane.The induced current through the resistor R is

The three loops of wire shown in the figure 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 emf induced in them?

A circular coil of radius 5.0 cm and resistance 0.20 Ω is placed in a uniform magnetic field perpendicular to the plane of the coil.The magnitude of the field changes with time according to B = 0.50e^-20t T.What is the magnitude of the current induced in the coil at the time t = 2.0 s?

A series LR circuit consists of a 2.0-H inductor with negligible internal resistance,a 100-ohm resistor,an open switch,and a 9.0-V ideal power source.After the switch is closed,what is the maximum power delivered by the power supply?

How much energy is stored in a room 3.0 m by 4.0 m by 2.4 m due to the earth's magnetic field with a strength of 5.0 × 10^-5 T? (μ₀ = 4π × 10^-7 T ∙ m/A)

The figure shows a bar magnet moving vertically upward toward a horizontal coil.The poles of the bar magnets are labeled X and Y.As the bar magnet approaches the coil it induces an electric current in the direction indicated on the figure (counter-clockwise as viewed from above).What are the correct polarities of the magnet?

You are designing a generator to have a maximum emf of 8.0 V.If the generator coil has 200 turns and a cross-sectional area of 0.030 m²,what should be the frequency of the generator in a uniform magnetic field of 0.030 T?

A conducting bar slides without friction on two parallel horizontal rails that are 50 cm apart and connected by a wire at one end.The resistance of the bar and the rails is constant and equal to 0.10 Ω.A uniform magnetic field is perpendicular to the plane of the rails.A 0.080-N force parallel to the rails is required to keep the bar moving at a constant speed of 0.50 m/s.What is the magnitude of the magnetic field?

Wire is wound on a square frame,30 cm by 30 cm,to form a coil of 7 turns.The frame is mounted on a horizontal shaft through its center (perpendicular to the plane of the diagram),as shown in the figure.The coil is in clockwise rotation,with a period of 0.060 s.A uniform,horizontal,magnetic field of magnitude 0.40 T is present.At a given instant,the plane of the coil forms a 60° angle with the horizontal,as shown.At that instant,what is the magnitude of the emf induced in the coil?

In an LC circuit containing a 40-mH ideal inductor and a 1.2-mF capacitor,the maximum charge on the capacitor is 45 mC during the oscillations.What is the maximum current through the inductor during the oscillations?

In the figure,a C-shaped conductor is in a uniform magnetic field B,which is increasing.The polarity of the induced emf in terminals X and Y is

A coil lies flat on a tabletop in a region where the magnetic field vector points straight up.The magnetic field vanishes suddenly.When viewed from above,what is the direction of the induced current in this coil as the field fades?

The figure shows three metal coils labeled A,B,and C heading towards a region where a uniform static magnetic field exists.The coils move with the same constant velocity and all have the same resistance.Their relative sizes are indicated by the background grid.As they enter the magnetic field the coils will have an induced electric current in them.For which coil will the current be the greatest?

A large magnetic flux change through a coil must induce a greater emf in the coil than a small flux change.

In the figure,a copper bar is in contact with a pair of parallel metal rails and is in motion with velocity ν.A uniform magnetic field is present pointing downward,as shown.The bar,the rails,and the resistor R are all in the same plane.The induced current through the resistor R is