Physics 202 MWF 12:40 Spring 1993 (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. An L-C circuit has an inductor with L = 0.80 H and a capacitor with C = 5.0 × 10^-10 F. During the current oscillations the maximum current in the inductor is 2.0 A. During the oscillations, what is the maximum energy stored in the capacitor?

Ans. __1.6 J__


(22 pts) 2.
a) The magnetic field B at all points in a circular region of radius a = 0.200 m is the same. It is directed into the plane of the paper, has an initial value of 4.0 T, and is increasing at a uniform rate of +0.20 T/s. A conducting wire loop with resistance R = 5.0 and radius r = 0.100 m is in the region of magnetic field with its center at the center of the field region. What are the magnitude and direction (clockwise or counterclockwise, as viewed in the diagram) of the current induced in the wire loop?

Ans. magnitude __1.26 × 10^-3 A__

direction __counterclockwise__

b) The electric field E at all points in a circular region of radius R = 0.200 m is the same. It is directed out of the plane of the paper, has an initial value of 400 V/m, and is decreasing at a uniform rate of -20 V/m. What are the magnitude and direction (left, right, up, down, into paper, out of paper) of the induced magnetic field at point a which is 0.40 m above the center of the region?

Ans. magnitude __1.11 × 10^-17 T__

direction __to right__

(16 pts) 3. In an attempt to make yet another movie the elderly crew of the starship Enterprise are traveling in the vicinity of the bright star Agge.

a) At a distance of 2.0 × 10¹⁰ m from the star the light from the star has an intensity of
5.0 × 10³ W/s². What is the total power output of the star?

Ans. __2.51 × 10²⁵ W__

b) Part of the light from Agge has wavelength 5.0 × 10^-7 m. At a distance of 5.0 × 10⁹ m from the star the magnetic field amplitude of the light with this wavelength is 4.0 × 10^-8 T. At this same distance from Agge what is the electric field amplitude E_max of the light with this wavelength?

Ans. __12 V/m__


(20 pts) 4. A rectangular loop of wire with resistance R = 2.0 is being pulled to the right out of a region of uniform magnetic field at a constant speed of 0.4 m/s. The magnetic field has magnitude 0.50 T and is directed into the plane of the paper. The loop has length 0.30 m and width 0.15 m.

a) What are the magnitude and direction (clockwise or counterclockwise) of the current induced in the loop?

Ans. magnitude __0.015 A__

direction __clockwise__

b) What are the magnitude and direction of the force that the magnetic field exerts on the loop?

Ans. magnitude __1.12 × 10^-3 N__

direction __to right (opposes the motion)__


(16 pts) 5. The circuit shown in the sketch has an emf = 90 V, a resistor R₁ = 40 a resistor R₂ = 30 , and an inductor L = 8.0 H.

a) Switch S is closed. At some time t afterwards the current in the inductor is increasing at a rate of i/t = 4.0 A/s. At this instant what is the current i₁ through R₁ and the current i₂ through R₂?

Ans. i₁ = __2.25 A__

i₂ = __1.93 A__

b) After the switch has been closed a long time it is opened again. Just after it is opened, what is the current through R₁?

Ans. i₁ = __3.0 A__


(12 pts) 6. A ray of light is incident in air on the top of a block of glass whose index of refraction is 1.32.

a) What is the critical angle for total internal reflection for light traveling in the glass and incident on the interface with air?

Ans. __49.2°__

b) What is the largest angle of incidence ø_a of the light on the top surface of the glass for which total internal reflection will occur at the vertical face (point A in the sketch)?

Ans. __59.5°__