| Physics | Arts and Sciences | University of Toronto | Libraries |

Postings

Questions

Some topics from the tutorial sessions:
  1. Newton is standing on the moon. He drops a big apple and a feather from the same height above the lunar surface. Which object reaches the surface of the moon first? Why?
  2. Which car is going faster, A or B? Assume there are equal intervals of time between the frames of both movies.
    car car car car
    (Car A)
    Car Car Car
    (Car B)
  3. A book about the laws of physics is at rest on a table on Earth. Identify the force(s) acting on the book and explain why it is not moving. Which of Newton's Laws of Motion are demonstrated by this example?
  4. How does Newton explain the elliptical motion of the planets?
  5. Mars follows an elliptical orbit around the Sun. Is the acceleration of Mars directed a. towards the Sun, b. away from the Sun, or c. along the direction of its velocity (at a tangent to the ellipse)?
  6. Suppose that the Earth was orbiting two large stars, instead of one. Would there be simple laws of planetary motion in this case? What type of motion would the Earth exhibit?
  7. According to Faraday and Maxwell, what mediates the forces between charged objects?
  8. Draw the electric field lines between two parallel oppositely charged metal plates. One plate has an excess of positive charges and other has an excess of negative charges. If a positron (an electron with a positive charge) is placed between the two plates, which way will it travel? Why? What eventually happens to the positron?
  9. What is wrong with the sound effect of an exploding spaceship that is heard in many science fiction/fantasy movies?
  10. How are sound waves converted into electrical waves in a telephone? Think about the motion of a magnet which is surrounded by a coil of wire.
  11. The Coyote hears the Road-Runner's voice at a higher pitch (frequency) compared to the pitch when the Road-Runner is at rest with respect to the Coyote. Is the Road-Runner moving towards or away from the Coyote? What phenomenon is illustrated by this example?
  12. What is the perihelion shift of the planet Mercury? How does the measurement of this quantity support the predictions of the General Theory of Relativity?
  13. Why does the photoelectric effect suggest that light has particle-like properties? Orange light can generate photoelectrons from the metal potassium, but red light cannot. Name another color of light which can produce the photoelectric effect in potassium and explain your answer.
  14. Suppose an atom has only three evenly spaced energy levels. How many lines would result in the spectrum of these atoms? How would the frequencies of these spectral lines compare?
  15. What does the double slit experiment using electrons tell us about the wave and particle nature of electrons?

Answers

Answers to selected homework questions:
  1. hw4 Hold a pencil to the left of your head. View the image of the pencil in a mirror. Draw a picture showing light waves originating from the tip of the pencil, reflecting from the mirror, and arriving at your eyes.
    A sketch of either circular waves or a profile of the oscillating E-field originating from the pencil tip, going to the mirror, and reflecting to the eye should be shown. The angle of incidence should be the same as the angle of reflection. Click the diagram to the right (thanks to Jimmy).
  1. Gandalf goes to the top of a mountain. He sends an orange pulse of light to his friend Frodo at the bottom of the mountain. If Frodo has a sensitive enough detector, what frequency of light does he measure?
    The frequency of the light is blue shifted. The measured frequency would be larger than that corresponding to orange. Here is why: Instead of being in a gravitational field, consider the observer to be in an elevator accelerating upwards in outer space. A pulse of light travels from the source S ahead of the elevator to the detector D which travels with the elevator. Since D moves towards the light pulse, the wave pattern according to D appears compressed. The wavelength is measured to be smaller. The frequency is larger compared to that observed when S and D are at rest with respect to one another. If the frequency is larger in an accelerated reference frame, then by the Principle of Equivalence, it will be larger in a gravitational field.

Links