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Unformatted text preview: University of the Philippines
College of Science PHYSICS 72 SET A First Semester 2010-2011
Third Long Examination National Institute of Physics 1St Sem AY 2010-2011 Physics 72 INSTRUCTIONS: Choose the best answer and shade the corresponding circle on your
answer sheet. To change your answer, cross out and sign your original answer and then
shade your new answer. No computational devices allowed (e.g. calculators, mobile phones).
Following instructions is part of the exam. Useful formulas: —IZEIEEEIEE nu . 4 3
Sphere (radIus = r) 4711' E 7LT
. Cylinder (radius =r,
hei ht = Useful constants:
e -1.60 x 10'19 C
me 9.1 x 10'31 kg
so 8.854 x 10'12 CZ/Nm2
k 8.988 x 109 Nmz/C2 For the next three numbers, consider an electromagnetic wave propagating in vacuum with
its electric ﬁeld given by E = 4c cos(2nz - 4nt) i in SI units. Note: c = speed of light in
vacuum. 1. Wavy. What is the direction of the wave propagation?
positive x-axis negative x-axis positive y-axis negative z-axis positive z-axis £11.50??? 2. WWF. What are the values of the wave's wavelength and frequency?
C. A = 1/(n) m; f: 1/(2n) Hz
D. A = 1 m; f = 2 Hz
E. ii = 2 m; f: 4 Hz 3. Max's. Which of the following statement/s does/do not conform to the Maxwell’s equations?
1. Electric field can exist in space even without magnetic field.
II. The induced electric field should be perpendicular to changing
magnetic field that produces it.
III. A point charge moving parallel to another moving point charge
experiences a magnetic field that is parallel to its direction of motion.
A. I only
B. III only
C. I and II 2|A National Institute of Physics 1St Sem AY 2010-2011 Physics 72 D. I and III
E. I, II and III 4. Mojo firefly. Consider a tiny firefly, flying in air, contained inside two concentric
spherical shells with different radii, 5-cm and 10-cm, respectively. Assuming that
both shells are totally absorbing of the light from the firefly with intensity Io, what
is the average radiation pressure exerted on each shell. A. 5-cm radius shell: Io/c ; 10-cm radius shell: Io/c B. 5-cm radius shell: Io/c; 10-cm radius shell: 2I0/c
C. 5-cm radius shell: 5Io/c; 10-cm radius shell: Io/c
D. 5-cm radius shell: Io/c; 10-cm radius shell: 10Io/c
E. 5-cm radius shell: 5Io/c; 10-cm radius shell: 10Io/c 5. CCI4. An electromagnetic wave propagates in carbon tetrachloride with a speed of
2.0 x 108 m/s. The relative magnetic permeability of carbon tetrachloride is 1.0. The
dielectric constant of carbon tetrachloride is closest to: A. 3.0
E. 2.0 6. Wavelength. A 2.0 x 1014 Hz electromagnetic wave propagates in carbon
tetrachloride with a speed of 5.0 x 108 m/s. The wavelength of the wave in carbon
tetrachloride is closest to: A. 1.0 x 10'7 m
B. 4.0 x 105 m
C. 2.5 X 10'6 m
D. 1.0 x 1022 m
E. 2.0 x 10'“ m 7. Index. The speed of yellow sodium light in a certain liquid is 1.5 x 108 m/s. The
index of refraction of this liquid for sodium light is approximately A. 2.0
E. 1.33 8. Glass-tic. Blue light with a wavelength of 425 nm passes from a vacuum into a glass lens; and the index of refraction is found to be 1.65. The glass lens is replaced
with a plastic lens. The index of refraction for the plastic lens is 1.50. In which one of the two lenses does the light have the greatest speed and what is that speed?
A. glass, 2.28 x 108 m/s
B. plastic, 2.13 x 108 m/s
C. glass, 1.82 x 108 m/s 3|A National Institute of Physics 10. 11. 12. 1st Sem AY 2010-2011 Physics 72 D. plastic, 2.0 x 108 m/s E. The speed of the blue light is the same in the vacuum and both lenses;
and it is 3.00 x 108 m/s. Antenna. At a distance 5 from the antenna, magnetic and electric field are
measured with amplitudes of 2E0 and 330. What is the intensity of the EM wave
that is detected at that distance from the antenna? A- (6EoBo)/IJ0
D. EoBo/IJD E. (4EoBo)/IJD Wavefront. In a certain region of space, radial rays emanate from a point light
source. Which of the following diagrams represent a cross-section of the
wavefronts in a plane? B A B. c
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Reflection. A horizontal ray is incident on a car side mirror whose plane is slightly tilted upward, as shown.
What is the angle between the incident and the reflected rays? A. 0° B. 10°
E. 70° Index. A dense transparent material makes light of wavelength 600 nm in air have
a wavelength of 450 nm inside it. What is the index of refraction of the material
A. 0.75 4|A National Institute of Physics 13. 14. 15. 16. 1st Sem AY 2010-2011 Physics 72 B. 1.00
Napasok na. A ray of light passes from different
materials with indices na, nb and nc as shown. What 11.. m. nc
can we conclude about the relationship of na, nb and -,___¥
nc? "‘ x
A. na =nh>nc B. na > nb = nC \ \ C. nb > na = nc D. h: > na > nb E. 17:: > nb > na Dispersion. Green and red lasers
simultaneously enter dense flint, whose GREEN
dispersion curve is shown in the figure. The
locations of the relative values of the green and \ RED
red wavelengths are also shown. Which of the following statements is true? . I , , , , A. Green light and red light have equal 0-3 0‘ 0";mee-:gm£31m)'2 H ‘5
speeds in dense flint.
Green light is faster than red light in dense flint.
Green light is slower than red light in dense flint.
Green light is always faster than red light.
Green light is always slower than red light. 'm
l Refractive index 11 F1909“ Malus Law. A beam of unpolarized light with intensity
In is incident upon two ideal polarizers oriented at 30°
from the vertical and another oriented at 120°. What
would be the intensity of light after it has passed through
the two polarizers? l A. Zero B. Incosz(30°) C. Incosz(120°) D. Incosz(30°)cosz(120°) E. In Scattering. Which of the following statements is definitely true about the
intensity of scattered (Rayleigh) light? I. The ratio of the intensity of scattered light of two different colors is
proportional to the inverse ratio of the wavelengths raised to the
fourth. II. The morning sky appears blue because red light is scattered better than blue light. 5|A National Institute of Physics 1St Sem AY 2010-2011 Physics 72 III. The sky at sunset appears red because only red light is left for the eye
to see. I only
I and II
I and III
E. I, II and III
17. Total Internal reflection. A light ray is incident with material ‘a’ with index of
refraction equal to one is totally reflected and makes a 30 degree angle with
respect to the vertical as shown. Which of the following is/are true?
1. na > nb
II. The critical angle is 30°
III. nb = (3/4)"2 POP? A. I B. II C. I and II D. I and III E. All of the above 18. Brewster's Angle. A light from material ‘a’ with
index of refraction (na) equal to 2 is polarized by
reflection as it hiis material ‘b’. The incident light
ray makes an angle equal to 60° with respect to
the vertical as shown. What is the index of
refraction of material ‘b’? A. (3)“2
E. 1 For the following two numbers, consider a convex mirror with a focal length of 34 cm.
19. Imahe. Which of the following best describes the image that is formed?
A. real, reduced, upright
B. real, magnified, upright
C. virtual, reduced, upright
D. virtual, magnified, upright
E. virtual, magnified, inverted 20. Oily. A curious physics 72 student immersed the same mirror in oil (n = 1.52).
What will be its focal length inside the medium? A. +34 cm
B. -34 cm
D. -17cm mA National Institute of Physics 1St Sem AY 2010-2011 Physics 72 E. Infinity For the next two questions, consider a thin converging lens where its second focal point, f12, coincides with the radius of curvature of another R thin converging lens with focal lengths f for both of 2 its sides. An extended object from a distance qu . . . .
is incident on to the left of the ﬁrst converging thin f1 1 f1 2 lens. [Note f11 = f12 = f] 21. Lens system. Where will the object for the second lens be formed? A. -fu
22. Lens system. Where will the final image be formed?
E. Infinity 23. Converging lens. Calvin’s picture is placed in front
of a converging lens with focal length f shown
below. Calvin’s picture seen with the naked eye is
shown in boxed picture below. Which of the ‘
following choices indicates the image seen by Andy observer
the observer? D picture lens IIA'IVD 24. Trinoma. Ana saw a lovely dress while window-shopping in Trinoma. She tried to
wear the dress inside a fitting room where she saw two parallel plane mirrors.
How many virtual images were formed if she stood between the two mirrors? A. 2 B. 4 C. 16 D 32 E. Infinite 7|A National Institute of Physics 25. 26. 27. 28. 29. 1st Sem AY 2010-2011 Physics 72 Fishy. A not-so-golden fish is at the center of a water-filled (nany water = 1.5)
spherical fish bowl with radius of 12 cm. What is the apparent position of the fish to an observer outside the bowl? A. 12 cm
B. -12 cm
C. 24 cm
D. -24 cm
E. Infinity Plane Mirror. Which of the following statements is/are true about the image of a
real object placed in front of a plane mirror?
I. The image formed is virtual
II. The image formed is upright
III. The magnitude of the image distance is always the same distance as
the object distance
IV. The image formed can be real I only II only III only I, II and III I, II, III and IV mpowa Lens. An object is placed 5 cm from a concave lens with focal length of -10cm. The
image is A. real, inverted and diminished B. real, inverted and enlarged C. real, upright and enlarged D. virtual, upright and enlarged E. virtual, upright and diminished Path Difference. Two identical point sources each produce coherent EM
radiation of the same wavelength A = 500.0 nm. One source is at (0, 1), while the
other is at (0, -1). Along which straight line is the interference always
XLHQ Phase Construction. Which of the following phase differences between two
coherent light waves will result in constructive interference? A. n/Z
B. 11; C. 31L/2
E. 51L/2 MA 1St Sem AY 2010-2011 National Institute of Physics 30. 31. 32. 33. 34. Physics 72 Width. Three 2-point slit interference setups, R, K, and M were prepared
identically except for the light wavelength used, AR > A; > AM. Arrange the
width of the bright fringes, W, of the three setups in the correct order. A.IIIIII
B. WR< WK< WM
C. W; < WK > WM
D. WR = WK = WM
E. WR > WK = WM Young_. You performed a classical two-slit experiment, using a laser with
wavelength A = 500.0 nm, and slit separation d = 5.0 mm. If you placed the screen
10.0 m away from the slits, which among the following distances from the
optical axis is/are the location(s) of a bright fringe?
I. 2.5 mm
II. 4.0 mm
III. 5.0 mm I only II only
I and III 00?? Fringe Logic. Three 2-slit interference setups, R, K, and M were prepared
identically except for the slit width used, all; > dK > d”. Arrange the three
setups according to width of the dark fringes. A. R > K > M B. R < M < K Ill-Ill
E R<K>M Anti-Reflection. Dr. Valdo decided to design an anti-reflection coating for
Silicon (n5. = 3) solar cells. What minimum thickness must he use to minimize
reflection (at A0 = 500 nm) if the material he’ll use for the coating is V-glass (n =
2.5)? A. 25 nm
B. 50 nm
C. 100 nm
D. 250 nm
E. 500 nm Intensity. What will happen to the intensity of a two slit interference pattern if the
intensity of the laser used is doubled? A. Doubled NA National Institute of Physics 1St Sem AY 2010-2011 Physics 72
E. Remains the same 35. 36. 37. 38. Phase Difference. Given a two slit interference experiment, a laser that has A =
600 nm was used. In the m = 1 (first from the center) bright band, what must be
the path difference of the two waves? A. 300 nm
B. 450 nm
C. 600 nm
D. 750 nm
E 900 nm Interference Patterns. Two glass slides
are configured as shown in the figure which
results in bright and dark bands along the
slides. What will happen to the spacing
between the bands when the height h is
doubled? Hint: assume everything else is
the same. A. Doubled \ B. Quadrupled " \ X\AH\\\ C. Halved k— != 10.0 (Sm—H
D. Quartered E. Remains the same Laser I. A laser beam of wavelength 600 nm passes through a slit producing a
bright diffraction pattern on a distant screen. If the first diffraction minima are at
i300, what is the width of the slit? A. 100 nm
B. 300 nm
C. 600 nm
D. 900 nm
E. 1200 nm Laser II. A monochromatic light of wavelength 400 nm passes through a slit of
width 100 pm. The diffraction pattern is observed on a screen 2 m away from the
slit. What is the width of the central bright maximum? A. 0.8 x 10'3m B. 1 x 10'3m
C. 1.6 x 10'3m
D. 8 x 10'3m E. 16 X 10'3 m 10|A National Institute of Physics 1St Sem AY 2010-2011 Physics 72 39. Five for Pattern. The five diffraction patterns below are observed when the
wavelength component of a tunable light source that passes through narrow slit is
tuned from red to blue. If the width of the slit and its distance to the screen are
kept constant, which pattern is most likely produced by the red wavelength? E .“ TI .5 TI .C C
6 6 9
6 6 40. The Fraction. What will happen to the width of the central maximum in a
diffraction pattern if the slit width and slit-to-screen distance are both halved?
A. Increases by a factor of 4
B. Increases by a factor of 2
C. Remains the same
D. Decreases by a factor of 2
E. Decreases by a factor of 4 41. Rainbow. Red, green and blue light with frequencies 400 x 1012 Hz, 526 x 1012
Hz and 631 x 1012 Hz, respectively, are, in turn, incident on a slit. Compare the
widths of each resulting central maximum. A. Wred < Wgreen < Wblue
B. Wred < Wblue < Wgreen
C. Wgreen < Wred < Wblue
D. Wblue < Wgreen < Wred
E. Wgreen < Wblue < Wred 42. Singkit. What will happen to the width of the central diffraction envelope in a
double slit experiment if the slit separation is increased without changing the slit width?
E. quadrupled 43. Intense. An interference pattern is formed by light of wavelength 500 nm passing
through two slits of width 0.5 mm separated by 1 mm. The slits are separated from 11|A National Institute of Physics 1St Sem AY 2010-2011 Physics 72 the screen by 1 m. What is the intensity at y = 1 mm in terms of the maximum
intensity Imax? I max
I max/ 2
I max/ 4 Imax/ 8
Zero moon? For the next two numbers, consider the interference pattern shown below. H m— -l m—U m=| 44. Grating. How many slit/s formed the interference pattern?
A. 1 slit
B. 2 slits
C. 4 slits
D. 8 slits
E. 16 slits 45. To the max. What is the maximum intensity in terms of the incident light intensity
In? A. In
E. 16Io SO. ISTHJS n?
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