Question 1

Suppose that you wish to construct a simple AC generator with an output of 12. V maximum when rotated at 60. Hz. A magnetic field of 0.050 T is available. If the area of the rotating coil is 100. cm², how many turns are needed?

Accepted Answer

The answer of Suppose that you wish to construct a...

Question 2

A transformer with 120. turns in its secondary supplies 12. volts at 220. ma to a toy train. The primary is connected across a 120. V wall outlet.
(a) How many turns are in the primary?
(b) What is the primary current?
(c) What power is delivered by the wall outlet?

Accepted Answer

The answer of A transformer with 120. turns in its...

Question 3

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?

Accepted Answer

The answer of The windings of a DC motor have...

Question 4

A 60. Hz AC generator produces a maximum emf of 170. V. What is the value of the emf 0.025 s after it has reached its maximum value?

Accepted Answer

The answer of A 60. Hz AC generator produces a...

Question 5

A 80. volt DC motor draws 4.0 A at its operating speed of 1500. rpm with an
armature resistance of 4.0 Ω.
(a) What is the starting current?
(b) What is the back emf when running normally?
(c) What series resistance could be added to limit the starting current to 10. A?

Accepted Answer

The answer of A 80. volt DC motor draws 4.0...

Question 6

A transformer has a turns ratio of 10. The primary voltage and current are 120. volts and 20. Amperes.
(a) What is the primary impedance (ratio of primary voltage to current)?
(b) What is the secondary impedance?

Accepted Answer

The answer of A transformer has a turns ratio of...

Question 7

FIGURE 23-5 
-A rectangular loop of wire carrying a current of 2.0 A that can rotate is placed in a magnetic field whose strength is 0.40 T, as shown in Figure 23-5. The length of the loop L is 0.16 m and its width w is 0.04 m. What is the magnetic flux through the loop when the plane of the loop is parallel to the magnetic field?

Accepted Answer

When the plane of the loop is parallel to the magnetic field, the angle between the magnetic field and the normal to the loop is 90 degrees, resulting in zero magnetic flux through the loop.

Question 8

A metal airplane flies horizontally at 200. m/s where the Earth's magnetic field
is vertical and is 45.0 μT. If the wingspan is 25.0 meters:
(a) what emf is induced across the wings?
(b) what wingspan would produce 1.0 volt emf?
(c) The plane reverses direction. Does the polarity of the wingtip emf change, i.e., if the left wing was positive, does it now become negative?

Accepted Answer

The answer of A metal airplane flies horizontally at 200....

Question 9

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?

Accepted Answer

The answer of A coil of 40. turns and cross-sectional...

Question 10

A coil of 160 turns and area 0.20 m² is placed with its axis parallel to a magnetic field of 0.40 T. The magnetic field changes from 0.40 T in the x-direction to 0.40 T in the negative x-direction in 2.0 s. If the resistance of the coil is 16 Ω, at what rate is power generated in the coil?

Accepted Answer

The answer of A coil of 160 turns and area...

Question 11

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?

Accepted Answer

The answer of An ideal transformer steps down 120. volts...

Question 12

FIGURE 23-5 
-A rectangular loop of wire carrying a current of 2.0 A that can rotate is placed in a magnetic field with a strength of 0.40 T as shown in Figure 23-5. 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 perpendicular to the magnetic field?

Accepted Answer

The magnetic flux (Φ) through the loop is given by Φ = B * A * cos(θ), where B is the magnetic field strength, A is the area of the loop, and θ is the angle between the magnetic field and the normal to the plane of the loop. When the plane of the loop is perpendicular to the magnetic field, θ = 0 degrees, and cos(θ) = 1. The area A = L * w = 0.16 m * 0.040 m = 0.0064 m². Therefore, Φ = 0.40 T * 0.0064 m² = 2.56 × 10^-3 T∙m², which rounds to 2.6 × 10^-3 T∙m².

Question 13

An ideal transformer has 60. turns on its primary coil and 300. turns on its secondary coil. If 120. V at 2.0 A is applied to the primary, what voltage and current are present in the secondary?

Accepted Answer

The answer of An ideal transformer has 60. turns on...

Question 14

The starting current in a DC motor is 20. A, but it normally operates on 110. volts with a back EMF of 90. volts.
(a) What is the resistance in the windings?
(b) What is the current at normal load?

Accepted Answer

The answer of The starting current in a DC motor...

Question 15

An AC generator rotating at 60. Hertz in a 300. Gauss field has 1000. turns and produces an rms voltage of 150. volts and an rms current of 70. Amperes.
(a) What is the peak current?
(b) What is the area of each turn in the coil?

Accepted Answer

The answer of An AC generator rotating at 60. Hertz...

Question 16

A power transmission line 50. km long has a total resistance of 0.60 Ω. A generator produces 100. V at 70. A. In order to reduce energy loss due to heating of the transmission line, the voltage is stepped up with a transformer with a turns ratio of 100:
1.
(a) What percentage of the original energy is lost when the transformer is used?
(b) What percentage of the original energy would be lost if the transformer were not used?

Accepted Answer

The answer of A power transmission line 50. km long...

Question 17

A circular coil of diameter 20. cm, with 16. turns is in a 0.13 Tesla field.
(a) Find the total flux through the coil when the field is perpendicular to the coil plane.
(b) If the coil is rotated in 10. ms so its plane is parallel to the field, find the average induced emf.

Accepted Answer

The answer of A circular coil of diameter 20. cm,...

Question 18

A step-down transformer is needed to reduce a primary voltage of 120. V AC to
6.0 V AC. What turns ratio is required?

Accepted Answer

The answer of A step-down transformer is needed to reduce...

Question 19

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

Accepted Answer

The answer of A 90.% efficient transformer supplies 3.0 Amperes...

Question 20

An eagle, with a wingspread of 2.0 m, flies due North at 8.0 m/s in a region where the vertical component of the earth's magnetic field is 0.2 × 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.)

Accepted Answer

The answer of An eagle, with a wingspread of 2.0...

Quiz 23: Magnetic Flux and Faradays Law of Induction

Suppose that you wish to construct a simple AC generator with an output of 12. V maximum when rotated at 60. Hz. A magnetic field of 0.050 T is available. If the area of the rotating coil is 100. cm2, how many turns are needed?

A transformer with 120. turns in its secondary supplies 12. volts at 220. ma to a toy train. The primary is connected across a 120. V wall outlet. (a) How many turns are in the primary? (b) What is the primary current? (c) What power is delivered by the wall outlet?

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?

A 60. Hz AC generator produces a maximum emf of 170. V. What is the value of the emf 0.025 s after it has reached its maximum value?

A 80. volt DC motor draws 4.0 A at its operating speed of 1500. rpm with an armature resistance of 4.0 Ω. (a) What is the starting current? (b) What is the back emf when running normally? (c) What series resistance could be added to limit the starting current to 10. A?

A transformer has a turns ratio of 10. The primary voltage and current are 120. volts and 20. Amperes. (a) What is the primary impedance (ratio of primary voltage to current)? (b) What is the secondary impedance?

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?

A coil of 160 turns and area 0.20 m2 is placed with its axis parallel to a magnetic field of 0.40 T. The magnetic field changes from 0.40 T in the x-direction to 0.40 T in the negative x-direction in 2.0 s. If the resistance of the coil is 16 Ω, at what rate is power generated in the 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?

An ideal transformer has 60. turns on its primary coil and 300. turns on its secondary coil. If 120. V at 2.0 A is applied to the primary, what voltage and current are present in the secondary?

The starting current in a DC motor is 20. A, but it normally operates on 110. volts with a back EMF of 90. volts. (a) What is the resistance in the windings? (b) What is the current at normal load?

An AC generator rotating at 60. Hertz in a 300. Gauss field has 1000. turns and produces an rms voltage of 150. volts and an rms current of 70. Amperes. (a) What is the peak current? (b) What is the area of each turn in the coil?

A circular coil of diameter 20. cm, with 16. turns is in a 0.13 Tesla field. (a) Find the total flux through the coil when the field is perpendicular to the coil plane. (b) If the coil is rotated in 10. ms so its plane is parallel to the field, find the average induced emf.

A step-down transformer is needed to reduce a primary voltage of 120. V AC to 6.0 V AC. What turns ratio is required?

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

Suppose that you wish to construct a simple AC generator with an output of 12. V maximum when rotated at 60. Hz. A magnetic field of 0.050 T is available. If the area of the rotating coil is 100. cm², how many turns are needed?

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?

A coil of 160 turns and area 0.20 m² is placed with its axis parallel to a magnetic field of 0.40 T. The magnetic field changes from 0.40 T in the x-direction to 0.40 T in the negative x-direction in 2.0 s. If the resistance of the coil is 16 Ω, at what rate is power generated in the coil?