PHY3054 - Exam 3 - Fall 1994 - Selman Hershfield
1. The conducting rod in Figure 1 moves producing a clockwise current of 8 Amperes. If the resistance of the circuit ABCD is 3 Ohms and the magnetic field is 3 Tesla out of the page, what the is the velocity of the rod?

1. 4 m/s to the right
2. 4 m/s to the left
3. 8 m/s to the left
4. 8 m/s to the right
5. none of the above

2. As shown in Fig. 2, a square loop of wire with resistance 10 Ohms is moved at a constant speed of 5 m/s through a region of magnetic field, B = 2 Tesla out of the page. What is the force on the loop when it is in the middle of the finite field region (see Figure 2)?

1. 0 Nt
2. 0.02 Nt to the right
3. 0.02 Nt to the left
4. 0.1 Nt to the right
5. 0.1 Nt to the left

3. In Figure 3.1 the current through the long wire increases. In Figure 3.2 the current is increased through the loop at left. What are the directions of the induced current around the loop in Fig. 3.1 and the right loop in Fig. 3.2?

1. clockwise in Fig. 3.1 and clockwise in Fig. 3.2
2. clockwise in Fig. 3.1 and counterclockwise in Fig. 3.2
3. counterclockwise in Fig. 3.1 and clockwise in Fig. 3.2
4. counterclockwise in Fig. 3.1 and counterclockwise in Fig. 3.2
5. none of the above

4. A coil with 80 turns, area 0.5 m2 , and resistance 40 Ohms is connected to a charge measuring instrument. Initially a magnetic field of 4 Tesla is in the plane of the coil. The coil is rotated quickly so that the magnetic field now makes at angle of 30 degrees with the plane of the coil (see Fig. 4). What is the net charge which flows through the circuit?

1. 1 Coulomb
2. 3 Coulomb
3. 4 Coulomb
4. 2 Coulomb
5. 5 Coulomb

5. A magnetic field of 1 Tesla is perpendicular to the plane of a circular loop of wire with radius 10 cm and resistance 5 Ohms. If in one second the loop is stretched so that its final radius is 17 cm, keeping the resistance the same, what is the magnitude of the induced current in the loop?

1. 6 mA
2. 12 mA
3. 18 mA
4. 24 mA
5. none of the above

6. In a vacuum the wavelength of orange light is 1.5 times the wavelength of violet light. What is the speed of orange light divided by the speed of violet light?

1. 0.67
2. 1.0
3. 1.5
4. 2.25
5. 3.0

7. The radius of the earth is 6 x 106 m, and the distance from the earth to the sun is 1.5 x 1011 m. If the power of the radiation hitting the earth is 2 x 1017 Watts, what is the net power radiated by the sun?

1. 1 x 1026 Watts
2. 2 x 1026 Watts
3. 3 x 1026 Watts
4. 4 x 1026 Watts
5. 5 x 1026 Watts

8. A satellite in outer space experiences light of intensity 1.5 kW m-2 . If the satellite has a perfectly reflecting sail normal to the incident light and with area 104 m2 , what is the net force on the satellite?

1. 5 x 10-5 Nt
2. 10-4 Nt
3. 5 x 10-4 Nt
4. 0.05 Nt
5. 0.1 Nt

9. At a distance of 2 km from a radio station, the maximum electric field is 0.3 V m-1 . Assuming that the antenna radiates equally in all directions, at what distance from the radio station is the maximum magnetic field equal to 10-10 Tesla?

1. 2 km
2. 20 km
3. 200 km
4. 2000 km
5. 105 km

10. Put your name, social security number, and test number correctly on the bubble sheet and the exam printout.

1. Done correctly.
2. Done incorrectly.
3. Done incorrectly.
4. Done incorrectly.
5. Done incorrectly.

11. Let f, c, and L be the frequency, speed, and wavelength of light traveling in a vacuum. If this light then goes into a piece of glass with index of refraction of 1.5, what are the new frequency, speed, and wavelength of the light?

1. f/1.5, c/1.5, L/1.5
2. f/1.5, c/1.5, L
3. f/1.5, c, 1.5 L
4. f, c/1.5, L/1.5
5. 1.5 f, c, L/1.5

12. Four polarizers are arranged as shown in Fig. 5. If I is the intensity of incoming unpolarized light, what is the intensity of the outgoing light?

1. 0
2. 0.1 I
3. 0.2 I
4. 0.3 I
5. 0.4 I

13. As shown in Fig. 6 a light ray is incident upon a plane of glass which covers water in a tank. What is the angle marked X in Fig. 6?

1. 22 degrees
2. 35 degrees
3. 41 degrees
4. 59 degrees
5. 68 degrees

14. The critical angle for total internal reflection when going from one type of glass to water is 56 degrees. If light has an angle of incidence of 20 degrees when going from the water to the glass, what is the angle of the transmitted ray to the normal of the interface?

1. 16.5 degrees
2. 17.7 degrees
3. 22.6 degrees
4. 24.4 degrees
5. no light is transmitted

15. Light is totally internally reflected in a triangular piece of glass as shown in Fig. 7. What is the minimum index of refraction of the glass for this to happen?

1. 0.87
2. 1.15
3. 1.5
4. 1.67
5. 2

16. An object is placed 0.4 meters in front of a concave mirror with radius 1 meter. Which of the following is true of the image formed?

1. The image is real and erect.
2. The image is real and inverted.
3. The image is virtual and erect.
4. The image is virtual and inverted.
5. Not enough information given.

17. In Figure 8 which of the principal rays is draw incorrectly?

1. Ray 1
2. Ray 2
3. Ray 3
4. Ray 4
5. All the rays are drawn correctly.

18. An image in a convex mirror with radius 1 m has a magnification of 1/3. What is the distance of the object from the mirror?

1. -0.33 m
2. 0.25 m
3. 0.33 m
4. 0.5 m
5. 1 m

19. Light coming from infinity in a glass rod is focused to a point as shown in Figure 9. What is the distance, d, of this point from the end of the glass rod?

1. 3.33 cm
2. 4 cm
3. 5 cm
4. 6.67 cm
5. 10 cm

20. A fish, which is 0.5 meters underwater, looks straight up at a fisherman, who is 1 meter above the water. If the index of refraction of water is 1.33 and the index of refraction of air is 1.00, how far above the water does the fish think the fisherman is?

1. 0.37 m
2. 0.66 m
3. 0.75 m
4. 1.00 m
5. 1.33 m

1. Answer = (1) 4 m/s to the right
2. Answer = (1) 0 Nt
3. Answer = (4) counterclockwise in Fig. 3.1 and counterclockwise in Fig. 3.2
4. Answer = (4) 2 Coulomb
5. Answer = (2) 12 mA
7. Answer = (5) 5 x 1026 Watts
8. Answer = (5) 0.1 Nt
9. Answer = (2) 20 km
10. Answer = (1) Done correctly.
11. Answer = (4) f, c/1.5, L/1.5
12. Answer = (3) 0.2 I
13. Answer = (5) 68 degrees
14. Answer = (1) 16.5 degrees