Download Physics116_L22

Physics 116
Session 22
Review: ray optics
Nov 4, 2011
R. J. Wilkes
Email: [email protected]
Announcements
•! Exam 2 is Monday!
•!
•!
All multiple choice, similar to HW problems, same format as Exam 1
•! YOU must bring a standard mark-sense (bubble) sheet
•!
Closed book/notes, formula page provided
•! You provide: bubble sheet, pencils, calculator, brain
Covers material in Chs. 25 - 27 (not including material from ch. 28
yesterday)
•!
Please take alternate seats for the exam (empty seat between
students) - Latecomers can sit at tables in front or back
•!
Today = review and ”practice exam” = examples similar to exam
questions
•!
Formula sheet is included in today’s slides and also posted on
website
Lecture Schedule
(up to exam 2)
Today
3
The story so far – stuff you have learned about in 116
(since exam 1):
•!Electromagnetic Waves
•!Energy and speed of EM waves
•!Polarization
•!Reflection and plane mirrors
•!Ray tracing
•!Spherical mirrors
•!Mirror equation
•!Refraction
•!Total internal reflection
•!Thin-lens equation
•!Rainbows & related phenomena
•!Human vision; the eye
•!Optical Instruments
•! Magnifying glass
•! Microscope
•! Telescope
•! Camera / projector
•! Formula page
1) The frequency of a microwave signal is 9.76 GHz. What is its wavelength in
meters?
A)! 3.07 ! 10-2 m
B)! 2.07 ! 10-2 m
C) 1.07 ! 10-2 m
D) 5.07 ! 10-2 m
E) 4.07 ! 10-2 m
Answer: A
! = c /f
2) The rms value of the electric field component of an electromagnetic wave is
27.2 N/C. What is the maximum value of the electric field?
A) 38.5 N/C
B) 19.2 N/C
C) 27.2 N/C
D) 47.4 N/C
E) 52.8 N/C
Answer: A
Answer: A
3) A 60.0 W light bulb radiates light uniformly in all different
directions. What is the average intensity of the light bulb at a
distance of 0.400 m from the bulb?
A) 14.9 W/m2
B) 37.2 W/m2
Answer: E
C) 27.4 W/m2
D) 11.9 W/m2 I = ! watts $ = ! 60W $
#" m 2 &% #" 4' R 2 &%
E) 29.8 W/m2
oops, the problem actually posted was:
" B2 %
" 60W %
I == $
= c $ '( B=
2
# 4! R '&
# µ0 &
Notice: since 60W is the timeaveraged power radiated by
the bulb, the B value we find
here is the RMS B, not the
maximum B value
=
( 60kg * m
( )
/ s 3 (4! ) 10 *7 "# kg / s 2 A %& ( m / A )
4! 0.49m 2 3 ) 10 8 m / s
2
(
( 60 ) 10 )
*7
=
)
( 60W ) (4! ) 10 *7 T * m / A
2
4! ( 0.7m ) 3 ) 10 8 m / s
)
(
)
" kg 2 / A 2 s 4 % = 2.02 ) 10-7 T
&
( 0.49 ) 3 ) 10 #
8
4) If the magnification of a mirror is negative, which of the
following is correct?
A)! The image is upright and the mirror is convex.
B) The image is inverted and the mirror is convex.
C) The image is inverted and the mirror is concave.
D) All of the previous answers can be correct.
E) None of the previous answers is correct.
Answer: C
negative M means inverted
Image in convex mirror is always upright
5) An object is located 3.8 m in front of a plane mirror. The
image formed by the mirror appears to be
A)! 1.9 m in front of the mirror.
B) on the mirror's surface.
C) 1.9 m behind the mirror's surface.
D) 3.8 m in front of the mirror.
E) 3.8 m behind the mirror's surface.
Answer: E
f=infinity for plane mirror
di = -do so equal distance behind
6) An object is 12 cm in front of a concave mirror, and the image
is 3.0 cm in front of the mirror. What is the focal length of the
mirror?
A) 0.25 cm
Answer: D
B) 15 cm
C) 4.0 cm
D) 2.4 cm
E) 1.3 cm
7) At what angle must a fish underwater look in order to see a
fisherman at the shore? (Note: n for water is 1.33.)
A)! 41.2°
B) 48.8°
C) 60.0°
D) 36.9°
E) 90.0°
Answer: B
8) A ray of light consisting of blue light (wavelength 480 nm) and red
light (wavelength 670 nm) is incident on a thick piece of glass at 80°.
What is the angular separation between the refracted red and
refracted blue beams while they are in the glass? (The respective
indices of refraction for the blue light and the red light are 1.4636 and
1.4561.)
n1
In class today I had the numbers
sin
!
=
sin
!
2
1
A)! 0.277°
reversed, sorry
n2
B) 0.455°
1
C) 0.330°
sin ! 2" BLUE =
sin80! = 0.6729 # ! 2" BLUE = 42.2887!
1.4636
D) 0.155°
1
E) 0.341°
sin !
=
sin80! = 0.6763 # !
= 42.5577!
2" RED
$! = 0.27
1.4561
2" RED
(roundoff may make your answer a bit different - choose the closest answer)
Answer: A
9) A nearsighted person has a far point that is 4.2 m from his eyes. What focal length
lenses in diopters he must use in his contacts to allow him to focus on distant objects?
A)! 0.48 diopters
B) -0.48 diopters
C) -0.36 diopters
D) -0.24 diopters
E) 0.24 diopters
We want a lens that makes an object at infinity appear to be
4.2 m away, so do=infinity, dI = - 4.2m
(minus sign because image is on same side of lens as object)
10) The total length of a telescope is 2.20 m and the focal length of
the eyepiece is 1.9 cm. What is the focal length of the objective?
A) 41 cm
B) 45 cm
C) 111 cm
D) 218 cm
E) 16 cm
Answer: D
See you Monday!
Please take alternate seats for the exam (empty
seat between students)
Latecomers can sit at tables in front or back