Exam 19: Electromagnetic Induction

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

As shown in the figure,two solenoids are in line.The switch S,initially closed,is suddenly opened.Just after opening S,what is the polarity of the induced emf in terminals X and Y?

A circular coil lies flat on a horizontal surface.A bar magnet is held fixed above the center of the coil with its north pole pointing downward.What is the direction of the induced current in the coil,as viewed from above?

A circular coil lies flat on a horizontal surface.A bar magnet is held above the center of the coil with its north pole pointing down.If the magnet is dropped from this position what is the direction of the induced current in the coil,as viewed from above?

A coil of wire containing N turns is in an external $\vec { B }$ field that is perpendicular to the plane of the coil and it steadily changing in magnitude.Under these circumstances,an emf ε is induced in the coil.If the rate of change of the magnitude of the $\vec { B }$ field and the number of turns in the coil are now doubled (but nothing else changes),what will be the induced emf in the coil?

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

A conducting rod whose length is ℓ = 1.60 m is placed on frictionless U-shaped metal rails that is connected to a lightbulb having a resistance of 4.00 Ω as shown in the figure.The rails and the rod are in the plane of the page.A constant uniform $\vec { B }$ field 2.20 T in magnitude is applied perpendicular to and out of the paper.An external force exerted on the rod moves the rod to the right with a constant speed of 6.00 m/s.At what rate is electric energy converted into internal energy in the lightbulb?

A bar magnet is oriented above a copper ring,as shown in the figure.If the magnet is kept fixed while the ring is dropped,what is the direction of the current induced in the ring,as viewed from below the ring?

The wire in the figure carries a current I that is increasing with time at a constant rate.The wire and the three loops are all in the same plane.What is true about the currents induced in each of the three loops shown?

The three loops of wire shown in the figure are all hanging in the same uniform magnetic field $\vec { B }$ that is perpendicular to the page and does not vary with time.Loop 1 swings back and forth like 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 coil lies flat on a horizontal tabletop in a region where the $\vec { B }$ field points straight down.The magnetic field disappears suddenly.When viewed from above,what is the direction of the induced current in this coil as the field disappears?

An ac generator consisting of a coil with N turns rotating at angular speed ω in an external magnetic field B produces a maximum emf ε₀.If you now decrease the number of turns in the coil to N/2 and at the same time cause it to rotate twice as fast,what will be the new maximum emf if you do not change any of the other quantities?

A airplane having a metal surface and a wingspan of 25.0 m flies horizontally at 200 m/s where the earth's $\vec { B }$ field is vertical with magnitude 45.0 μT. (a)What emf is induced across the wings? (b)What wingspan would the plane need to produce 1.00-V emf across its wings? (c)The plane now reverses direction.Does the polarity of the wingtip emf change? That is,if the left wing was positive before,does it now become negative?

An ac generator with a total resistance of 12 Ω contains 100 flat loops of wire,each with an area of 0.090 m².The loops rotate at 60 rev/s in a $\vec { B }$ field of magnitude 0.50 T.What is the maximum possible induced current?

The area of a rectangular loop of wire is 3.6 × $10 ^{- 3}$ $m ^ { 2 }$ The loop is placed in a uniform $\vec { B }$ field that changes steadily from 0.20 T to 1.4 T in 1.6 s.The plane of the loop is perpendicular to the direction of the $\vec { B }$ field.What is the magnitude of the induced emf in that loop?

At a certain instant,coil A is in a 10-T external magnetic field and coil B is in a 1-T external magnetic field.Both coils have the same area and are oriented at right angles to the field.Which coil will have a greater emf induced in it?

According to Lenz's law,the induced current in a circuit always flows to oppose the external magnetic field through the circuit.

A flat circular coil having 16 turns,each of diameter 20 cm,is in a uniform and steady 0.13-T $\vec { B }$ B field. (a)Find the total magnetic flux through the coil when the field is perpendicular to the plane of the coil. (b)If the coil is rotated in 10 ms so its plane is parallel to the $\vec { B }$ field vector,find the average induced emf in the coil.

A round flat metal coil has 180 turns and negligible resistance.It is connected in a series circuit with a $17 - \Omega$ resistor,with nothing else in the circuit.You measure that a $6.0 - \mathrm { A }$ current flows through the resistor when a magnetic field through the coil,perpendicular to its area,is changing at $3.0 \mathrm {~T} / \mathrm { s } .$ What is the radius of the coil?

According to Faraday's law,a coil in a strong magnetic field must have a greater induced emf in it than a coil in a weak magnetic field.