Exam 19: Electromagnetic Induction

A flat circular loop having one turn and radius 5.0 cm is positioned with its plane perpendicular to a uniform 0.60-T $\vec { B }$ field.The area of the loop is suddenly reduced to essentially zero in 0.50 ms.What emf is induced in the loop?

A long straight wire lies on a horizontal table and carries an ever-increasing current toward the north.Two coils of wire lie flat on the table,one on either side of the wire.When viewed from above,the direction of the induced current in these coils is

As shown in the figure,a metal bar is in contact with a pair of metal parallel rails.A steady uniform magnetic field B,perpendicular to the plane of the rails and pointing outward from the page,is present.The bar is in downward motion with velocity of magnitude ν.The direction of the induced current through the resistor R is

An outer metal ring surrounds an inner metal ring,as shown in the figure.The current in the outer ring is counterclockwise and decreasing.What is the direction of the induced current in the inner ring?

As shown in the figure,a metal bar is in contact with a pair of parallel rails and is in motion with an upward velocity of magnitude ν.A uniform magnetic field is present, $\vec { B }$ field vector directed downward as shown.The direction of the induced current through the resistor R is

A rectangular loop of wire that can rotate about an axis through its center is placed between the poles of a magnet in a $\vec { B }$ field of 0.40 T,as shown in the figure.The length of the loop L is 0.16 m and its width w is 0.040 m.What is the magnetic flux through the loop when the plane of the loop is parallel to the $\vec { B }$ field?

A transformer is a device used to

A conductor is formed into a flat loop that encloses an area of $1.0 \mathrm {~m} ^ { 2 }$ The plane of the loop is oriented at a 30.0° angle with the xy-plane.A uniform time-varying $\vec { B }$ field is oriented parallel to the z-axis.If the emf induced in the loop is $25.0 \mathrm {~V}$ what is the rate at which the magnitude of the $\vec { B }$ field strength is changing?

A flat rectangular coil with dimensions of 8.0 cm × 10 cm is dropped from a zero magnetic field position into a 1.4-T $\vec { B }$ field in 0.10 s.The coil has 60 turns and is perpendicular to the $\vec { B }$ field.What is the average induced emf in the coil as a result of this action?

A flat coil is wrapped with 200 turns of very thin wire on a square frame with sides 18 cm long.A uniform magnetic field is applied perpendicular to the plane of the coil.If the magnitude of the $\vec { B }$ field changes uniformly from 0.50 T to 0.00 T in 8.0 s,find the emf induced in the coil.

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

It is known that birds can detect the earth's magnetic field,but the mechanism of how they do this is not known.It has been suggested that perhaps they detect a motional emf as they fly north to south,but it turns out that the induced voltages are small compared to the voltages normally encountered in cells,so this is probably not the mechanism involved.To check this out,calculate the induced voltage across the wingtips of a wild goose with a wingspan of $1.2 \mathrm {~m}$ if it is flying directly south at $13 \mathrm {~m} / \mathrm { s }$ at a point where the earth's $\vec { B }$ field is 5.0 ×10^-5 T directed downward from the horizontal by $40 ^ { \circ }$

An eagle,with a wingspread of 2.0 m,flies toward the north at 8.0 m/s in a region where the vertical component of the earth's $\vec { B }$ field is 0.20 × 10^-4 T.What emf would be developed between the eagle's wing tips? (It has been speculated that this phenomenon could play a role in the navigation of birds,but the effect is too small,in all likelihood.)

A closed flat loop conductor with radius $2.0 \mathrm {~m}$ is located in a changing uniform magnetic field.If the emf induced in the loop is $2.0 \mathrm {~V}$ what is the rate at which the magnitude of the $\vec { B }$ field is changing if the $\vec { B }$ field vector is oriented perpendicular to the plane in which the loop lies?

An ideal step-down transformer is needed to reduce a primary voltage of 120 V to 6.0 V.What must be the ratio of the number of turns in the secondary to the number of turns in the primary?

The wire in the figure carries a steady current I.What is true about the currents induced in each of the three loops shown? The wire and the three loops are all in the same plane.

A flat coil is in a uniform magnetic field.The magnetic flux through the coil is greatest when the plane of its area is

A flat coil having 160 turns,each with an area of 0.20 m²,is placed with the plane of its area perpendicular to a 0.40T $\vec { B }$ field.The magnitude of the $\vec { B }$ field changes uniformly from 0.40 T in the +x direction to 0.40 T in the -x direction in 2.0 s.If the resistance of the coil is 16 Ω,at what rate is power generated in the coil during this change?

As shown in the figure,a battery supplies a steady current to the solenoid on the left.The two solenoids are moving toward each other with speeds v.The direction of the induced current through the resistor R is

As shown in the figure,a metal bar is in contact with a pair of parallel rails.A steady,uniform,magnetic field B is present directed to the right.The bar is moving upward with velocity of magnitude ν.What is the polarity of the induced emf in terminals X and Y?