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KOÇ UNIVERSITY
SCIENCE 106
FASCINATING WORLD OF LIGHT
Alphan Sennaroğlu
MIDTERM EXAM 2
Maximum Score = 100 points
Time allowed = 90 minutes
Closed-book Exam
NOTE ON ACADEMIC INTEGRITY
Academic dishonesty, in particular, cheating during the examination, will not be
tolerated and disciplinary action will be taken against those involved.
DIRECTIONS
1) PLEASE CHECK TO MAKE SURE YOUR EXAM BOOKLET HAS 7 PAGES.
3) CALCULATORS ARE NOT ALLOWED.
NAME: _____________________________________________________________
DEPARTMENT:_____________
SIGNATURE:_______________________
PART 1 (55 POINTS):______
PART 2 (45 POINTS):______
TOTAL SCORE :
______
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PART 1: SHORT-ANSWER QUESTIONS (55 POINTS)
Question 1: (9 points): Refraction of Waves
1
AIR
Boundary
WATER

(a) (7 pts) Above, you see a plane wave passing from air into water at oblique incidence. 1 is the
angle of incidence in air and 2 is the angle of refraction in water. Two consecutive wavefronts in
air and water are shown. The arrows point along the direction of wave motion in each medium.
Use simple trigonometric relations and the basic characteristics of waves to obtain the expression
for sin 1 / sin  2 in terms of the wave velocities in air and water.
(b) (2 pts) How does your answer to part (a) differ from the result that Newton found by assuming
that light consists of tiny particles like billiard balls. You do not need to derive his result. Just
state the difference in one sentence.
Question 2: (8 points)
Write Maxwell’s 4 equations. No equations are needed. Just the qualitative statements.
1)__________________________________________________________________________________
2)__________________________________________________________________________________
3)__________________________________________________________________________________
4)__________________________________________________________________________________
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Question 3: (11 pts) Young’s Double-Slit Experiment (5 points)
P
yn
S2
d
S1
L
(a) (2 pts) What is the relation between the disyances S1P and S2P if constructive interference occurs
at P?
(b) (2 pts) What is the relation between the distances S1P and S2P if destructive interference occurs at
P.
(c) Suppose that P is the location of the nth bright fringe on the screen. The distance of P from the
center bright is yn. Also, d is the slit separation and L is the distance of the slits from the screen.
Use simple trigonometry to find the relation between yn, L, d, and the wavelength  of the light.
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Question 4: (6 points)
(4pts) Briefly give the story of the Poisson’s spot. (2 pts) What was the important conclusion that was
drawn from here?
Question 5: (4 points)
Sketch the electric field lines around a negative point charge shown below.
Question 6 (4 pts)
Below, you see the cross section of a wire carrying electric current into the paper. Sketch the magnetic
field arrows around the wire.
X
Question 7 (5 pts) Fill in the Blanks
(a) (2 pts) After James Clerk Maxwell proposed the existence of electromagnetic waves, he calculated that
the speed of electromagnetic waves in vacuum is _______.
(b) (3pts) This result suggested that_____________________________________________________.
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Question 7 (4 pts)
Sketch an electromagnetic wave which moves to the left. Clearly show the direction of oscillation of the
electric field, magnetic field, and wave motion.
Question 8: Fill in the Blanks (4 points)
(a) (2 pts) The phenomenon of ______________________explains the beautiful colors of butterfly wings.
(b) (2 pts) Magnetic fields produce forces on current carrying conductors. A widely used device based on
this principle is _________________________.
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PART 2: MULTIPLE-CHOICE QUESTIONS (45 POINTS) (Each question is 3 points)
1) (3 pts) A water wave moves with a velocity of 30 m/sec. If the frequency is 5Hz then
(a) the period is 6 seconds.
(b) the wavelength is 150 meters.
(c) the period is 150 seconds.
(d) the wavelength is 6 meters.
2) (3 pts) As a water wave passes from deep to shallow water,
(a) the velocity remains the same.
(b) both frequency and the wavelength decrease.
(c) the wavelength becomes shorter but the frequency stays the same.
(d) the frequency becomes shorter but the wavelength stays the same.
3) (3 pts) Which of the following is not in general correct about waves?
(a) A wave is a moving pattern.
(b) Waves of all types travel with the same velocity.
(c) Waves refract while going from one medium to another.
(d) Wave velocity depends on the characteristics of the medium.
4) (3 pts) Two waves are moving in opposite directions on a hose as shown below. The shape on the right
is the inverted version of the shape on the left. The initial separation is also shown in the figure. Each
wave is moving with a velocity of 5 m/s. After how long, will the hose look flat instantaneously?
(a) 1 sec (b) 2 secs (c) 3 secs (d) 4 secs.
20m
(5) (3 pts) According to Faraday’s law of induction
(a) no isolated magnetic pole exists in nature.
(b) a time varying electric field produces a magnetic field.
(c) a time varying magnetic field produces an electric field.
(d) a static electric charge produces magnetic fields.
(6) (3 pts) The index of refraction of a certain optical medium is 3. This means that light moves with a
velocity of
(a) c/1.5
(b) 3c
(c) c/9
(d) c/3
in this medium.
(7) (3 pts) Consider the refraction of light as it goes from medium 1 to medium 2. The speed of the wave is
v1 in medium 1 and v2 in medium 2. Also, the frequency of the wave is f1 in medium 1 and f2 in medium 2.
Which of the following is correct?
(a) f1/f2 is equal to v1/v2.
(b) If v1 is greater than v2, the ray refracts away from the normal.
(c) If v1 is greater than v2, the ray refracts toward the normal.
(d) f1/f2 is equal to v2/v1.
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(8) (3 pts) Consider the double-slit experiment performed with different colors of light. The slit separation
and the distance to the screen are kept constant. Which of the following is correct?
(a) the separation between the bright fringes is larger for red light than for blue light.
(b) the separation between the bright fringes does not depend on the color of the light.
(c) the separation between the bright fringes is smaller for red light than for green light.
(d) the separation between the bright fringes is smaller for yellow light than for blue light.
(9) (3 pts) When the separation between two charged objects is 3 cm, the force of attraction is 9 Newtons.
If the separation is decreased to 1 cm without changing the charge on the objects, the force becomes
a) 27 N b) 1 N c) 3 N
d) 81 N
(10) ( 3pts) Which of the following is incorrect?
a) neutrons are lighter than electrons
b) electrons are lighter than neutrons
c) protons are positively charged
d) neutrons and protons have about the same mass
(11) (3 pts) Which of the following is correct about magnets/magnetic field lines?
(a) It is possible to separate the north and south poles of a magnet by cutting it into smaller pieces.
(b) Magnetic field lines point from positive to negative electric charges.
(c) Magnetic field lines point along the direction of force on the north pole of a tiny magnet.
(d) Magnetic field lines point from negative to positive charges.
(12)(3 pts) According to Oersted’s discovery
(a) static electric charges produce electric fields.
(b) moving magnets generate electric fields.
(c) magnetic fields produce forces on electric currents.
(d) electric currents produce magnetic fields.
(13) (3 pts) Which of the following is not ionizing radiation?
(a) radio waves
(b) uv
(c) x-rays
(d) gamma rays
(14) (3 pts) The distance between the crests of a wave is called
(a) wavelength
(b) period
(c) frequency
(d) velocity.
(15) (3 pts) Consider two polarizers with the transmission axes oriented at 90 degrees with respect to each
other so that no light passes through the region of overlap. What happens if a third polarizer is placed in
between the two polarizers with its transmission axis at some angle (between 0 and 90 degrees) with
respect to those of the original polarizers?
(a) No light still passes through.
(b) All of the incident light now passes through.
(c) Some of the incident light now passes through, the transmission amount depends on the orientation of
the third polarizer.
(d) Independent of the orientation of the third polarizer, exactly half of the light will now go through.
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