1. clamatoman

    How many Photons per second are entering the pupil?

    1. Homework Statement (a)Estimate the number of photons per second emitted by a 100-W lightbulb, assuming a photon wavelength of 550nm.(b) A person can just see this bulb for a distance of 800m, with the pupil dilated to 7.5mm. How many photons per second are entering the pupil? 2. Homework...
  2. RoboNerd

    Question on lightbulb brightness in circuit analysis

    1. Homework Statement 2. Homework Equations I know that power of a lightbulb/resister is I^2 * R 3. The Attempt at a Solution OK. Here's my attempt: Let's consider the situation where we do not close the lightbulb and assume that the wires and switch are ideal because they have no...
  3. RoboNerd

    Lightbulbs and a battery circuit

    1. Homework Statement 2. Homework Equations no equations 3. The Attempt at a Solution I know that we will have an equal current flowing through bulbs 1 and 2 when we connect them in parallel in accordance with kirchoff's voltage law which says that the voltage drops around both paths must...
  4. N

    B Lightbulb physics problem?

    The light in a lightbulb is the result of an increase in temperature. This increase is created by both a highter elektrical resistance in the wire and a highter elektric current. But a higher resistance results in a lower elektric current (I) (I=V/R), so it is both increasing and decreasing the...
  5. Svein

    Lightbulb jokes

    Q: How many science fiction writers does it take to change a lightbulb? A: Two, but it's actually the same person doing it. He went back in time and met himself in the doorway and then the first one sat on the other one's shoulder so that they were able to reach it. Then a major time paradox...
  6. TheAxolotl

    How is the vacuum in a light bulb sealed?

    I understand that one would use a vacuum pump to evacuate a light bulb, but once a vacuum is created, how is the bulb sealed without air coming in?
  7. skepticwulf

    Power of lightbulb problem

    1. Homework Statement A 100-W, 120-V lightbulb has a resistance of 12 ohm when cold (20°C) and 140 ohm when on (hot). Calculate its power consumption (a) at the instant it is turned on, and (b) after a few moments when it is hot. 2. Homework Equations P=IV, P=I^'R, P=V^2/R 3. The Attempt at...
  8. N

    Lightbulb I/V curve question

    The question I've been given this question by a teacher and I'm clueless as to what b) and c) are. Could you please help? I would really appreciate it. The prize is a place to see a lecture on quantum simulation at our local University. Thank you :)
  9. robotpie3000

    How can a light bulb be made more efficient so that it emits more light in the visible spectrum?

    I just finished an experiment on blackbody radiation, and one of the post lab questions asked me on the possible ways in which a light bulb can be made more efficient such that the majority of the light it produces falls in the visible spectrum. After some quick research I think one of the...