The mass of an electron and its antiparticle, a positron, is 0.511 MeV/c2 . In order to produce an electron-positron pair, a gamma ray must have an energy larger than 1.022 MeV because __________

Fill in the blank(s) with correct word


of the equivalence of mass and energy

Physics & Space Science

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An aluminum cantilever beam (E 5 72 GPa) with a square cross section and span length L 5 2.5 m is sub- jected to uniform load q 5 1.5 kN/m. The allowable bending stress is 55 MPa. The maximum deflection of the beam is approximately:

(A) 10 mm
(B) 20 mm
(C) 30 mm
(D) 40 mm

Physics & Space Science

A 400-g piece of metal at 100°C is dropped into a 100-g aluminum cup containing 500 g of water at 15°C. The final temperature of the system is 40°C

What is the specific heat of the metal, assuming no heat is exchanged with the surroundings? The specific heat of aluminum is 900 J/(kg?K) A) 1900 J/(kg?K) B) 2270 J/(kg?K) C) 3300 J/(kg?K) D) 3800 J/(kg?K) E) 4280 J/(kg?K)

Physics & Space Science

Light pollution makes it impossible to see faint objects

Indicate whether the statement is true or false

Physics & Space Science

Which of the following statements is not true about x-ray scattering (in crystals) and its importance?

a. It showed that electromagnetic radiation diffracts and interferes like a wave. b. It ruled out the corpuscle model of light. c. It helped uncover the crystalline structures of many solids. d. It helped scientists more accurately measure x-ray wavelengths. e. Rosalind Franklin used the scattering to model molecules of DNA.

Physics & Space Science