Physics 202 MWF 10:20 Spring 1994 (Ford)
Exam III Chapts. 32,33,35,36 in SZY College Physics


Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.


(14 pts) 1.
a) A ray of light traveling in glass is incident on the surface of the glass at an angle ø_a with respect to the normal. It is observed that there is no light refracted into the air when ø_a is greater than 30°. What is the refractive index of the glass?

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b) In air where the speed of light is 3.0 × 10⁸ m/s the wavelength of a beam of light is 800 nm. If the same light passes from air into a block of plastic where the wave speed is 2.0 × 10⁸ m/s, what is the wavelength of the light in the plastic?

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(14 pts) 2. The energy stored in a long, straight coil that has 2000 turns is 80 J when the current in the coil is 3.0 A.

a) What is the inductance L of the coil?

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b) What is the magnetic flux through each turn of the coil, when I = 3.0 A?

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(14 pts) 3. The radio transmitter in an airplane broadcasts at a frequency of 1240 × 10³ Hz with a power output of 2.6 × 10³ W. Assume that the radiation is emitted uniformly in all directions. The speed of the waves in air is 3.0 × 10⁸ m/s.

a) What is the intensity, in W/m², of the radiation at a distance of 200 m from the transmitter?

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b) At a distance of 200 m from the transmitter, what is the amplitude of the magnetic field of the radio waves?

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(20 pts) 4. Consider the circuit shown in the sketch, where = 80 V, R₁ = 4.0 , R₂ = 20 , and L =0.30 H. Initially the switch S is open and there are no currents.

a) Just after the switch is closed, what is the voltage v_ab across R₁? Which of the points a or b is at higher potential?

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b) Just after the switch is closed, what is the voltage v_de across L? Which of the points d or e is at higher potential?

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After the switch is left closed a long time (many time constants) it is opened again.

c) Just after the switch is opened again, what is the voltage v_cd across R₂? Which of the points c or d is at higher potential?

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d) Just after the switch is opened again, what is the voltage v_ab across R₁? Which of the points a or b is at higher potential?

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(18 pts) 5. There is a uniform magnetic field B in a cylindrical region of radius a =0.40 m. B is directed into the plane of the paper, has an initial value of 2.0 T, and is increasing in magnitude at a uniform rate of +0.05 T/s. A conducting metal ring with resistance 5.0 and radius r = 0.90 m encircles the field region, with the center of the ring at the center of the field region.

a) When the magnetic field is 2.0 T, what is the magnitude of the magnetic field flux through the metal ring?

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b) While the magnetic field is increasing in magnitude, what is the magnitude of the emf induced in the metal ring?

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c) Is the induced current in the ring in the counterclockwise or clockwise direction?

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(20 pts) 6. A rectangular loop of wire that is 0.40 m by 0.15 m is being pulled into a region of uniform magnetic field B that is directed into the plane of the paper. An external force F_ext = 0.30 N must be applied to the loop to maintain a constant speed of 8.0 m/s. The current induced in the loop is 0.50 A.

a) What is the magnitude of the magnetic field B?

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b) What is the direction of the current induced in the loop (clockwise or counterclockwise)?

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c) What is the magnitude of the emf induced in the loop?

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d) What is the resistance R of the loop?

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