Question 1

A loop of wire is rotated about a diameter (which is perpendicular to a given magnetic field.) In one revolution the induced current in the loop reverses direction how many times?
A) 4
B) 1
C) 0
D) 3
E) 2

Accepted Answer

The induced current in the loop reverses direction twice in one revolution. This happens because as the loop rotates through the magnetic field, the sides of the loop that cut through the magnetic field lines change direction relative to the field. This change in direction relative to the magnetic field occurs twice per revolution, leading to two reversals in the direction of the induced current.

Question 2

A horizontal metal bar rotates at a constant angular velocity w about a vertical axis through one of its ends while in a constant magnetic field B that is directed down. The emf induced between the two ends of the bar is A) constant and proportional to the product B . B) variable with a maximum of B ². C) constant and proportional to the product B²². D) variable with a maximum of B . E) constant and proportional to the product B ².

Accepted Answer

The answer of A horizontal metal bar rotates at a...

Question 3

A lightbulb is plugged into a household outlet, and one of the wires leading to it is wound into a coil. Now a slug of iron is slid into the coil. What effect will this have?
A) The lamp will get brighter because there will be an induced emf that will drive more current through the lamp.
B) The lamp will dim because a back emf will be produced by the coil, and this will reduce the current flowing in the coil and the lamp.
C) This will have no effect on the brightness of the lamp.
D) The lamp will dim because energy will now be dissipated in the iron.
E) This will not affect the lamp's brightness because the coil will shift the phase, but not the magnitude, of the current through the lamp.

Accepted Answer

Inserting an iron slug into the coil increases the coil's inductance, which in turn induces a back electromotive force (emf) when the current through the coil changes. This back emf opposes changes in the current, effectively reducing the current flowing through the circuit and thus dimming the lamp.

Question 4

A transformer is a device that
A) increases the power level of a circuit.
B) operates only on AC.
C) operates on either DC or AC.
D) operates only on DC.

Accepted Answer

Transformers operate only on alternating current (AC) because their function relies on the changing magnetic field created by AC to induce a current in another coil, thereby transferring energy from one circuit to another. DC does not create a changing magnetic field, so transformers cannot work with direct current (DC).

Question 5

Alternating current and voltage (AC), rather than direct current and voltage (DC), are used for domestic electrical power. The reason for this is based on one of the following physical principles. Which one?
A) Opposite electric charges attract each other, and like charges repel each other.
B) When the number of magnetic field lines passing through a circuit changes, a voltage is generated in the circuit.
C) When a current flows through a wire, a magnetic field is created.
D) When a current flows through a resistance, heat is generated.
E) When a current-carrying wire is placed in a magnetic field, it may experience a force if properly oriented.

Accepted Answer

Alternating current (AC) is used for domestic electrical power primarily because of the principle of electromagnetic induction, as described in option B. This principle allows for the efficient generation and transmission of electricity over long distances. AC can be easily transformed to higher or lower voltages, which reduces energy loss during transmission.

Question 6

James Clerk Maxwell presented the "complete" theory of electromagnetism as how many equations?
A) 1
B) 4
C) 3
D) 2
E) 5

Accepted Answer

James Clerk Maxwell presented the "complete" theory of electromagnetism as four equations, now known as Maxwell's equations. These equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.

Question 7

The tail of a comet is primarily caused by
A) eddy currents.
B) nuclear magnetism.
C) radiation pressure.
D) Coulomb repulsion.
E) electromagnetic induction.

Accepted Answer

The tail of a comet is primarily caused by radiation pressure from the Sun, which pushes dust and gas away from the comet's nucleus, creating the tail.

Question 8

Electromagnetic radiation of wavelength 3.5 meters is which type?
A) FM-radio
B) visible
C) ultraviolet
D) microwaves
E) AM-radio

Accepted Answer

The answer of Electromagnetic radiation of wavelength 3.5 meters is...

Question 9

Electromagnetic radiation of wavelength 0.3 pico-meters is which type?
A) gamma rays
B) ultraviolet
C) FM-radio
D) visible
E) X-rays

Accepted Answer

Gamma rays have wavelengths shorter than 0.01 picometers.

Question 10

Electromagnetic radiation of wavelength 2.5 cm is which type?
A) microwaves
B) AM-radio
C) FM-radio
D) ultraviolet
E) visible

Accepted Answer

Microwaves are electromagnetic waves with wavelengths ranging from about 1 millimeter to 1 meter, which includes the 2.5 cm wavelength specified in the question.

Question 11

Electromagnetic radiation of wavelength 200. nano-meters is which type?
A) ultraviolet
B) microwaves
C) AM radio
D) visible
E) X-rays

Accepted Answer

Electromagnetic radiation with a wavelength of 200 nanometers falls within the ultraviolet (UV) range. UV light has wavelengths shorter than visible light but longer than X-rays.

Question 12

A flux of 4 × 10^-5 Wb is maintained through a coil for 0.5 s. What emf is induced in this coil by this flux? A) No emf is induced in this coil. B) 4 × 10^-5 V C) 6 × 10^-5 V D) 2 × 10^-5 V E) 8 × 10^-5 V

Accepted Answer

If the magnetic flux through a coil is constant, as in this case, no change in flux occurs over time, and therefore, no emf is induced according to Faraday's law of electromagnetic induction.

Question 13

The cross-sectional area of an adjustable single loop is reduced from 1.0 m² to 0.25 m² in 0.10 s. What is the average emf that is induced in this coil if it is in a region where B = 2.0 T upward, and the coil's plane is perpendicular to B? A) 0 V B) 15 V C) 12 V D) 21 V E) 18 V

Accepted Answer

The average emf (ε) induced in a coil when its area changes can be calculated using Faraday's law of electromagnetic induction, which is ε = -ΔΦ/Δt, where ΔΦ is the change in magnetic flux and Δt is the change in time. The magnetic flux (Φ) is given by Φ = B*A*cos(θ), where B is the magnetic field strength, A is the area of the coil, and θ is the angle between the magnetic field and the normal to the plane of the coil. Since the coil's plane is perpendicular to B, cos(θ) = 1. The change in area (ΔA) is 1.0 - 0.25 = 0.75 m^2. Therefore, ΔΦ = B*ΔA = 2.0 T * 0.75 m^2 = 1.5 Wb. Given Δt = 0.10 s, the average emf is ε = -ΔΦ/Δt = -1.5 Wb / 0.10 s = -15 V. The negative sign indicates the direction of the induced emf, which is not required here, so the magnitude of the emf is 15 V.

Question 14

The flux through a coil changes from 4 × 10^-5 Wb to 5 × 10^-5 Wb in 0.1 s. What emf is induced in this coil? A) 3 × 10^-4 V B) 5 × 10^-4 V C) 7 × 10^-4 V D) 1 × 10^-4 V E) 4 × 10^-4 V

Accepted Answer

The induced emf (ε) is calculated using Faraday's law: ε = -ΔΦ/Δt. Here, ΔΦ = (5 - 4) × 10^-5 Wb = 1 × 10^-5 Wb and Δt = 0.1 s. Thus, ε = -(1 × 10^-5 Wb) / 0.1 s = -1 × 10^-4 V. The magnitude is 1 × 10^-4 V.

Question 15

A very long solenoid has 1.0 × 10⁶ turns per meter and a cross-sectional area of 2.0 × 10⁶m². A short, secondary coil with 1.0 × 10³ turns is wound over the solenoid's midpoint. What emf is induced in the secondary coil if the current in the solenoid is changing at a rate of 4.0 A/s? A) 1.6 V B) 1.0 V C) 4.4 V D) 2.7 V E) 0.52 V

Accepted Answer

The answer of A very long solenoid has 1.0 ×...

Question 16

Suppose that the maximum rate of change of current in a "high power" transmission line is 10⁴ A/s. How large a coil (area) placed 10. meters from the line would have 120. volts (max) induced in it? A) 2. × 10³ m² B) 6. × 10³ m² C) 6. × 10⁴ m² D) 2. × 105³ m² E) 6. × 10⁵ m²

Accepted Answer

The answer of Suppose that the maximum rate of change...

Question 17

A generator coil rotates through one revolution 60 times each second. The frequency of the emf is
A) 30 Hz.
B) 60 Hz.
C) (60/  ) Hz.
D) 120 Hz.
E) 60  Hz.

Accepted Answer

The answer of A generator coil rotates through one revolution...

Question 18

The coil of a generator has 50 loops and a cross-sectional area of 0.25 m². What is the maximum emf generated by this generator if it is spinning with an angular velocity of 4.0 rad/s in a 2.0 T magnetic field? A) 400. V B) 0. V C) 50. V D) 100. V E) 75. V

Accepted Answer

The maximum emf (ε) generated by a generator is given by the formula ε = NABω, where N is the number of loops, A is the area, B is the magnetic field, and ω is the angular velocity. Substituting the given values: ε = 50 * 0.25 * 2.0 * 4.0 = 100 V.

Question 19

The coil of a generator rotates through one complete turn in a uniform magnetic field 50. times every second. When this generator is connected to an external load, the current through the load reverses directions
A) 100 times every second.
B) 50 times every second.
C) 200 times every second.
D) 25 times every second.
E) 75 times every second.

Accepted Answer

The coil of a generator produces one complete cycle of alternating current (AC) with each rotation. Since it rotates 50 times every second, it completes 50 cycles per second. Each cycle of AC includes two reversals of current direction (once when the current goes from positive to negative and once when it goes from negative to positive), resulting in 100 reversals of current direction every second.

Question 20

An AC generator has 80. rectangular loops on its armature. Each loop is 12. cm long and 8.0 cm wide. The armature rotates at 1200. rpm about an axis parallel to the long side. If the loop rotates in a uniform magnetic field of 0.30 T, which is perpendicular to the axis of rotation, what will be the maximum output voltage of this generator?
A) 220 V
B) 124 V
C) 167 V
D) 120  V
E) 182 V

Accepted Answer

The answer of An AC generator has 80. rectangular loops...

Quiz 20: Electromagnetic Induction and Waves

A loop of wire is rotated about a diameter (which is perpendicular to a given magnetic field.) In one revolution the induced current in the loop reverses direction how many times?

A horizontal metal bar rotates at a constant angular velocity w about a vertical axis through one of its ends while in a constant magnetic field B that is directed down. The emf induced between the two ends of the bar is

A lightbulb is plugged into a household outlet, and one of the wires leading to it is wound into a coil. Now a slug of iron is slid into the coil. What effect will this have?

A transformer is a device that

Alternating current and voltage (AC) , rather than direct current and voltage (DC) , are used for domestic electrical power. The reason for this is based on one of the following physical principles. Which one?

James Clerk Maxwell presented the "complete" theory of electromagnetism as how many equations?

The tail of a comet is primarily caused by

Electromagnetic radiation of wavelength 3.5 meters is which type?

Electromagnetic radiation of wavelength 0.3 pico-meters is which type?

Electromagnetic radiation of wavelength 2.5 cm is which type?

Electromagnetic radiation of wavelength 200. nano-meters is which type?

A flux of 4 × 10^-5 Wb is maintained through a coil for 0.5 s. What emf is induced in this coil by this flux?

The cross-sectional area of an adjustable single loop is reduced from 1.0 m² to 0.25 m² in 0.10 s. What is the average emf that is induced in this coil if it is in a region where B = 2.0 T upward, and the coil's plane is perpendicular to B?

The flux through a coil changes from 4 × 10^-5 Wb to 5 × 10^-5 Wb in 0.1 s. What emf is induced in this coil?

A very long solenoid has 1.0 × 10⁶ turns per meter and a cross-sectional area of 2.0 × 10⁶m². A short, secondary coil with 1.0 × 10³ turns is wound over the solenoid's midpoint. What emf is induced in the secondary coil if the current in the solenoid is changing at a rate of 4.0 A/s?

Suppose that the maximum rate of change of current in a "high power" transmission line is 10⁴ A/s. How large a coil (area) placed 10. meters from the line would have 120. volts (max) induced in it?

A generator coil rotates through one revolution 60 times each second. The frequency of the emf is

The coil of a generator has 50 loops and a cross-sectional area of 0.25 m². What is the maximum emf generated by this generator if it is spinning with an angular velocity of 4.0 rad/s in a 2.0 T magnetic field?

The coil of a generator rotates through one complete turn in a uniform magnetic field 50. times every second. When this generator is connected to an external load, the current through the load reverses directions