The following questions for physics assignment: 1. If the power of a laser is 60
ID: 1602949 • Letter: T
Question
The following questions for physics assignment:
1. If the power of a laser is 60 mW, how much energy is transferred to the patient's eye during a 30s treatment?
2. Bright narrow fringes are observed on a screen in front of a diffraction grating. The entire experiment is immersed in water. Which of the following do you expect to happen to the fringes?
a) They get closer together
b)They get further apart
c) They remain at the same spacing
3. Which of the following statements about the photoelectron effect is NOT correct?
a. Photoelectrons produce a photocurrent when they travel to an electrode which has a positive potential compared to the metal surface.
b. The emission of photoelectrons is independent of the wavelength of the light used
c. The incident photon must have a certain minimum energy to cause a photoelectron to be emitted
d. The emission of photoelectrons can be stopped by applying a positive Stopping Potential to the metal surface
4. The Heisenberg Uncertainty Principle can be used to calculate the uncertainty in the energy of an emitted photon from a state with lifetime .
Calculate the energy uncertainty for a state with a lifetime of 3.8 picoseconds, expressing your answer in eV to 2 sf.
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Explanation / Answer
1. P = 60 mW = 60 x 10^-3 W
energy = P t
= (60 x 10^-3) (30 )
= 1.8 J
hence energy transferred to eye is 1.8 J .
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