Physics 262 Test #1 L Spring 2004 Prof. Price

NAME(print)____________________

Instructions: READ each problem. Do required calculations on this examination paper. Use diagrams! Show equations used and mark answer clearly (BOXED) and also mark appropriate answer on blue answer sheet. In all cases, select the answer that is best. RTDP = A

For the first three questions use these answers: a. resistance

b. reactance

c. capacitance

d. impedance

e. inductance

1. The combination of resistance and reactance in the correct form represents ______________-.

2. A coil of wire is used to introduce ___________ into an electrical circuit.

3. The effect of a capacitor and/or inductor on an A.C. circuit is called ___________.

4. What direct current will produce the same amount of thermal energy (power dissipation) in a resistor, as an alternating current with a maximum value of 2.6 amperes?
1. 2.6 A
2. 1.3 A
3. 1.8 A
4. 1.5 A
5. 2.0 A

5. An A.C. generator provides 200 volts to the primary coil (with 50 turns) of a transformer. If the secondary coil has 20 turns, what is the secondary voltage out?
1. 80 volts
2. 500 volts
3. 10 volts
4. 20 volts
5. 200 volts

6. A transformer on a utility pole operates at 8.5 kV (a.c.) on the input side. It supplies electricity to houses at 120 Volts. (Both voltages are rms). If this is an ideal transformer, no losses and power factor of one, what is the turns ratio N primary/ N secondary ?
1. 120
2. 71
3. 1020
4. 14
5. 0.014

7. A group of electrons executing simple harmonic motion in a wire (forced by an a.c. generator) will:
1. only dissipate energy as heat
2. cause the wire to oscillate
3. will cause an EM wave to be radiated
4. will cause a current to flow through the air
8. The electromagnetic spectrum is made up of a number of regions, each assigned a name, depending on the wavelengths involved. In order of increasing frequency these are:
1. radio waves, x-rays, microwaves, visible light, ultraviolet, infrared, gamma rays
2. microwaves, radio waves, infrared, visible, gamma rays, x-rays
3. radio waves, infrared, visible, ultraviolet, x-rays, gamma rays, microwaves
4. radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays
5. gamma rays, x-rays, ultraviolet, visible, infrared, microwaves, radio waves

9. What is the radiation force from the Sun on a dust particle (mass = 3 micrograms) with a cross section of one square micron? Assume the radiation is completely absorbed. The dust particle is at the distance of the Earth from the Sun (150 million kilometers). The power output of the Sun is 3.9 e26 Watts.
1. 4.3 e-18 N
2. 1.3 e-9 N
3. 4.3 e-6 N
4. 5.7 e-16 N
5. 1.7 e-8 N

10. Same answer as number (9).

11. The Poynting vector for an electromagnetic wave always points:

1. toward the source of the radiation
2. in the direction the wave is moving
3. perpendicular to the way the wave is moving
4. in the direction of the electric field in the wave
5. Does not apply to EM waves.

12. Natural light passed through a polarizing filter has:
1. only Io/3 compared to its original intensity.
2. A greatly reduced B field.
3. Suffered no effect.
4. Lost half of its intensity.
5. Lost intensity depending on the square of the cosine of the angle between the light and the normal to the filter.

For the next six questions use these answers: a. reflection

b. refraction

c. dispersion

d. diffraction

e. interference

13. When light strikes glass at an angle, some is __________ through the glass.
14. When you have two apertures in the same opaque plane and illuminated by coherent light, you will find an_______________ pattern on a screen at a distance in front of the apertures.
15. _______________ is understood best in terms of Huygen’s radiators at every point on a wavefront.
16. When a light ray emerging from under water reaches the surface, it will appear to come from a point shallower than it really comes from. Why?
17. Shimmering bands of color on the surfaces of soap bubbles are due to _____________
18. The separation of white light into colors by a prism is due to _____________.

19. The Sun is about 150 million kilometers away. The time for light to travel this distance is about:
1. 4.5 e18 sec
2. 8 sec
3. 8 min
4. 8 hr
5. 17 min

20. The time averaged energy in a sinusoidal EM wave is:
1. Mostly electrical
2. Slightly more electrical than magnetic
3. Equally divided between electric and magnetic fields
4. Slightly more magnetic
5. Overwhelmingly magnetic

21. When the distance between a point source of light and a light meter is reduced from six meters to three meters, the intensity of the illumination at the meter will the original value multiplied by:
1. 4
2. 2
3. ½
4. ¼
5. 9

22. When light travels from medium X to medium Y as shown:
1. both the speed and the frequency decrease
2. both the speed and the frequency increase
3. both the speed and the wavelength decrease
4. both the speed and the wavelength increase
5. We cannot say what happens—we are not told the value of indices of refraction.

23. A virtual image is one:
1. toward which light rays converge but do not pass through
2. from which light rays diverge but do not pass through
3. from which light rays diverge as they pass through
4. toward which light rays converge and pass through
5. you cannot see

24. The focal length of a spherical mirror is N times its radius of curvature, where N is:
1. ¼
2. ½
3. 1
4. 2
5. 4

25. And erect object is located between a concave mirror and its focal point. Its image is:
1. virtual, erect, and larger than the object
2. virtual, inverted, and smaller than the object
3. real, erect, and larger than the object
4. real, erect, and smaller
5. real, inverted, larger

26. A convex spherical mirror is has a focal length of 12 cm. If an object is placed 6.0 centimeters in front

of it, the image position is:

1. 4 cm behind the mirror
2. 4 cm in front of the mirror
3. 12 cm behind the mirror
4. 12 cm in front of the mirror
5. at infinity

27. A ‘wave front’ is a surface of constant:
1. phase
2. frequency
3. wavelength
4. amplitude
5. speed

28. In Young’s double slit experiment, the center of a bright fringe occurs whenever waves from the slits differ in the distance they travel by a multiple of:
1. a quarter of a wavelength
2. a half a wavelength
3. a wavelength
4. three quarters of a wavelength
5. none of the above

29. A soap film, 4 e-5 cm thick, is illuminated by white light, normal to its surface. The index of refraction of the film is 1.50. Which visible wavelengths will be intensified in the reflected beam?
1. 400nm and 600nm
2. 480nm and 800nm
3. 360nm and 533 nm
4. 400nm and 800nm
5. 510nm and 710nm

30. The rainbow seen after a rain shower is caused by:
1. diffraction
2. interference
3. refraction
4. polarization
5. absorption

31. Consider a single-slit diffraction pattern caused by a slit of with a. There is a minimum if sinθ is equal to:

a. exactly λ/a

b. slightly more than λ/a

c. slightly less than λ/a

d. exactly λ/2a

e. slightly more than λ/2a

32. Two slits of width a and separation d are illuminated by a beam of light of wavelength λ. The separation of the interference fringes on the screen a distance D away is:

a. la/D b. ld/D c. lD/d d. dD/l e. lD/da

33. To obtain greater dispersion by a diffraction grating:
1. the slit width should be increased
2. the slit width should be decreased
3. the slit separation should be increased
4. the slit separation should be decreased
5. more slits should be added to the system

34. Bragg’s Law for x-ray diffraction is 2dsinq = ml , where the quantity d is the:
1. height of the unit cell
2. smallest interatomic distance
3. distance from detector to sample
4. distance between the planes of atoms
5. usual calculus symbol for a differential

If you think a question was poorly worded or confusing—describe it here and tell me how you would have done it better.

If you think there was no right answer on any question describe it here and give me the right answer.

Thank you. J