Exam 19: Electromagnetic Induction

An electromagnetic flowmeter is useful when it is desirable not to interrupt the system in which the fluid is flowing (such as the blood in an artery during heart surgery).Such a device is illustrated in the figure.The conducting fluid moves with speed v in a tube of diameter d.Perpendicular to this tube is a magnetic field B.A voltage V is induced between opposite sides of the tube due to the motion of the conducting fluid in the magnetic field.For a certain case,B = 0.120 T,d = 1.2 cm,and the measured voltage is $V = 2.88 \mathrm { mV }$ Determine the speed of the fluid.

An ideal step-up transformer doubles a primary voltage of 110 V.What is the ratio of the number of turns in its primary coil to the number of turns in the secondary coil?

A flat square coil of wire with 15 turns and an area of 0.40 m² is placed with the plane of its area parallel to a 0.75-T $\vec { B }$ field.The coil is flipped so its plane is perpendicular to the $\vec { B }$ field in a time of 0.050 s.What is the magnitude of the average induced emf in the coil?

As shown in the figure,two parallel wires carry a current I in opposite directions,and this current is decreasing.A rectangular loop is centered between the wires.The direction of the induced current through the resistor R is

The wire in the figure carries a current I that is decreasing 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?

Two solenoids are close to each other,as shown in the figure,with the switch S open.When the switch is suddenly closed,which way will the induced current flow through the galvanometer in the left-hand solenoid?

As shown in the figure,a straight wire carries a steady current I.A metal bar is in contact with a pair of rails and is in upward motion with velocity of magnitude ν.The polarity of the induced emf in terminals X and Y is

As shown in the figure,two solenoids are side by side.The switch S is initially open.When S is suddenly closed,the direction of the induced current through the resistor R is

As shown in the figure,a wire and a 10-Ω resistor are used to form a circuit in the shape of a square with dimensions 20 cm by 20 cm.A uniform but non-steady $\vec { B }$ field is directed into the plane of the circuit.The magnitude of the $\vec { B }$ field is steadily decreased from 2.70 T to 0.90 T in a time interval of 96 ms.What is the induced current in the circuit,and what is its direction through the resistor?

A coil lies flat on a level tabletop in a region where the $\vec { B }$ field vector points straight up.The $\vec { B }$ field suddenly grows stronger in magnitude.When viewed from above,what is the direction of the induced current in this coil as the field increases?

As shown in the figure,one end of a metal bar is in contact with a circular rail and the other end is pivoted at P.A steady uniform,magnetic field B into the page is present.As the bar rotates about point P in a clockwise direction,the direction of the induced current through the resistor R is

A constant uniform magnetic field of 0.50 T is applied at right angles to the plane of a flat rectangular loop of area 3.0 × $10^{ - 3}$ $m ^ { 2 }$ If the area of this loop changes steadily from its original value to a new value of 1.6 × 10^-3 m² in 1.6 s,what is the emf induced in the loop?

As shown in the figure,a region of space contains a uniform $\vec { B }$ field of magnitude 2.8 T,directed straight into the plane of the page in the region shown.Outside this region the magnetic field is zero.A rectangular loop measuring 0.20 m by 0.60 m and having a resistance of 2 Ω is being pulled into the magnetic field by an external force,as shown. (a)What is the direction (clockwise or counterclockwise)of the current induced in the loop? (b)Calculate the magnitude of the external force F_ext that is required to move the loop at a constant speed of 3.9 m/s.

A long vertical wire carries a steady 70 A current.As shown in the figure,a pair of horizontal rails are 0.20 m apart.A 20-Ω resistor connects points a and b,at the end of the rails.A bar is in contact with the rails,and is moved by an external force with a constant horizontal velocity of 0.90 m/s to the right,as shown.The bar and the rails have negligible resistance.At the instant that the bar is 0.20 m from the wire,what are the induced current in the resistor and its direction through the resistor? (μ₀ = 4π × 10^-7 T ∙ m/A)

A bar magnet is oriented above a copper ring,as shown in the figure.The magnet is dropped and passes completely through the ring.As viewed from above,what is the direction of the current induced in the ring after the magnet has completely passed through the ring and is somewhat below it?

A circular conducting loop with a radius of $0.50 \mathrm {~m}$ and a small gap filled with a $10.0 - \Omega$ resistor is oriented in the $x y - p l a n e .$ If a uniform $\vec { B }$ field of $1.0 \mathrm {~T}$ making an angle of $30 ^ { \circ }$ with the $\text { z-axis, }$ increases to $10.0 \mathrm {~T} ,$ in $4.0 \mathrm {~s}$ what is the magnitude of the current that will be induced in the loop if it has negligible resistance?

A circular coil with 600 turns has a radius of 15 cm.The coil is rotating about an axis perpendicular to a magnetic field $\vec { B }$ of 0.020 T in magnitude.If the maximum induced emf in the coil is 1.6 V,at what angular frequency is the coil rotating?

A bar magnet is pushed through a coil of wire of cross-sectional area 0.020 m² as shown in the figure.The coil has seven turns,and the rate of change of the magnitude of the $\vec { B }$ field in it due to the motion of the bar magnet is 0.040 T/s.What is the magnitude of the induced emf in that coil of wire?

As shown in the figure,a coil of wire is placed in the xy-plane,centered on the z-axis.A solenoid is centered on the z-axis and is carrying a steady dc current.Which one of the following actions will not result induce an emf in the coil?

A flux of 4.0 × 10^-5 T ∙ m² is maintained through a coil of area 7.5 cm² for 0.50 s.What emf is induced in this coil during this time by this flux?