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Exam 25: EM Induction and Em Waves

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Question 71

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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 strength of the magnetic 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?

A) 5.6 × 10^-3 V
B) 5.6 × 10^-2 V
C) 5.6 × 10^-1 V
D) 5.6 × 10^-4 V
E) 5.6 × 10^-5 V

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Question 72

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A rectangular loop of wire that can rotate about an axis through its center is placed between the poles of a magnet in a magnetic field with a strength 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 magnetic field?

A) 13 × 10^-3 T ∙ m²
B) 2.6 × 10³ T ∙ m²
C) 0.80 T ∙ m²
D) 2.6 × 10^-3 T ∙ m²
E) 0 T ∙ m²

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Question 73

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The area of a rectangular loop of wire is 3.6 × $10 ^{- 3}$ $m ^ { 2 }$ . The loop is placed in a uniform magnetic 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 magnetic field. What is the magnitude of the induced emf in that loop?

A radio transmitter is operating at an average power of $4.00 \mathrm {~kW}$ and is radiating uniformly in all directions. What is the average intensity of the signal $8.00 \mathrm {~km}$ from the transmitter?

A circular coil of copper wire is lying flat on a horizontal table. A bar magnet is held above the center of the coil with its south pole downward. The magnet is released from rest and falls toward the coil. As viewed from above, what is the direction of the current induced in the coil as the magnet approaches the coil?

What is the wavelength of a photon having energy 2.00 eV? (c = 3.00 × 10⁸ m/s, h = 6.626 × 10^-34 J ∙ s, 1 eV = 1.60 × 10^-19 J)

The following items are positioned in sequence: A source of a beam of natural light of intensity I₀, three ideal polarizers A, B, and C; and an observer. Polarizer axis angles are measured clockwise from the vertical, as viewed by the observer. The axis angle of polarizer A is set at 0° (vertical) , and the axis angle of polarizer C is set at 50°. The axis angle of polarizer B is set at 120°. What is ratio of the intensity of the beam at the observer to the intensity I₀ of the source?

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

An 8.0-mW laser beam emits a cylindrical beam of single-wavelength sinusoidal light 0.90 mm in diameter. What is the rms value of the electric field in this laser beam? (ε₀ = 8.85 × 10^-12 C²/N ∙ m², μ₀ = 4π × 10^-7 T ∙ m/A, c = 3.0 × 10⁸ m/s)

A flat circular loop of radius 0.10 m is rotating in a uniform magnetic field of 0.20 T. Find the magnetic flux through the loop when the plane of the loop and the magnetic field vector are at an angle of 30°.

As shown in the figure, the orientation of the transmission axis for each of three ideal polarizing sheets is labeled relative to the vertical direction. A beam of light, polarized in the vertical direction, is incident on the first polarizer with an intensity of 1.00 kW/m². What is the intensity of the beam after it has passed through the three polarizing sheets when θ₁ = 30°, θ₂ = 30°, and θ₃= 60°?

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 light source radiates 60.0 W of single-wavelength sinusoidal light uniformly in all directions. What is the amplitude of the electric field of this light at a distance of 0.400 m from the bulb? (ε₀ = 8.85 × 10^-12 C²/N ∙ m², μ₀ = 4π × 10^-7 T ∙ m/A, c = 3.00 × 10⁸ m/s)

If the sunlight from a star peaks at a wavelength of 0.55 µm, what temperature does this imply for the surface of that star? The constant in Wien's law is 0.00290 m ∙ K.

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

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 field changes uniformly from 0.50 T to 0.00 T in 8.0 s, find the emf induced in the coil.

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?

A coil of wire containing N turns is in an external magnetic field that is perpendicular to the plane of the coil and it steadily changing. Under these circumstances, an emf ε is induced in the coil. If the rate of change of the magnetic 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?

How far does light travel in 1.0 μs? (c = 3.0 × 10⁸ m/s)

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?