Exam 1, PH204, July 19, 2012, for Dr. Harold Williams
With Answers
Question 1:
1) How long (in ns) does it take light to travel 2 m in vacuum?
Answer 6.6 ns
2) What distance does light travel in water during the time that it travels 2.0 m in vacuum? Use
1.33 for the index of refraction for water.
Answer 1.5 m
3) What distance does light travel in glass during the time that it travels 2.0 m in vacuum? Use 1.5
for the index of refraction for glass.
Answer 1.34 m
Question 2:
A double slit illuminated with light of wavelength 644 nm forms a diffraction pattern on a screen
6 cm away. The slit separation is d = 2783 nm. What is the distance Δx between orders m = 14
and m = 9?
A) 6.94 × 107 nm
B) 129.64 × 107 nm
C) 13.88 × 107 nm
D) 3.47 × 107 nm
Answer: A
Question 3:
A plane on one side and convex on the other side glass lens has an index of refraction of n=1.5
and the convex side has a radius of curvature of 50 cm, what is the focal length of the lens.
Please use the corrected formulae we went over in class yesterday not the incorrect one given in
the lab manual.
Question 4:
A convex lens has a focal length of 45 cm and an object is placed in front of it 55 cm. What is the image
distance?
What is the magnification of the image?
If the object is 2cm high what is the image height?
Is the image real or virtual?
Is the image up right or inverted?
Please draw a ray diagram and label everything clearly!
Question 5:
A concave mirror has a focal length of 50 cm and an object is placed in front of it 20 cm. What is the
image distance?
What is the magnification of the image?
If the object is 3cm high what is the image height?
Is the image real or virtual?
Is the image up right or inverted?
Please draw a ray diagram and label everything clearly!
Question 6:
Light having a speed in vacuum of 3.0 × 108 m/s enters a liquid of refractive index 2.0. In this
liquid, its speed will be:
A) 6.0 × 108 m/s
B) 3.0 × 108 m/s
C) 1.5 × 108 m/s
D) 0.75 × 108 m/s
E) None of the above choices are correct.
Answer: C
Question 7:
A ray in air is incident on a glass plate whose index of refraction is 1.42. The angle of refraction
is one-half the angle of reflection. The angle of refraction is closest to:
A) 45°
B) 43°
C) 41°
D) 39°
E) 37°
Answer: A
Question 8:
A telescope made with two convex lenses whose objective lens is 40 cm and whose eyepiece lens is 4
cm has a magnification of what?
Is the image right side up or inverted?
Of you look at something far away like the moon the distance between the lenses is how far?
What will be the best optical resolution in radians if the wavelength is 500 nm and the diameter of the
objective lens is 6 cm?
Question 9:
A metal sphere is insulated electrically and is given a charge. If 25 electrons are added to the
sphere in giving a charge, how many Coulombs are added to the sphere? The charge on an
electron is 1.6 × 10-19 C.
A) - 4.0 × 10-18 C
B) - 4.0 × 10-20 C
C) - 40 C
D) - 25 C
Answer: A
Question 10:
If a negative charge of 4 C is placed 2 m from the center of the question 10 sphere what will be
the force on the charge 2 meters away and what direction will the force be? Please draw a
clearly labeled picture as well.
Question 11:
An electron of mass 9.11 × 10-31 kg is accelerated from rest with a potential difference of 2000
volts. What is the kinetic energy in electron volts?
What is the kinetic energy in Joules?
What is the velocity of the electron?