Physics Question of The Week (5)

1. Electrons are ejected from a surface with speeds ranging up to 4.6 x 10⁵ m/s when light with a wavelength  λ = 625 nm is used.  

        a)    What is the work function of this surface?  

        b)    What is the threshold frequency for this surface?  

Answer Key for Physics Question of The Week (4)

F = qvB = mv² / r

F = (1.6 x 10^-19)(2 x 10⁷)(0.1)

   = 0.32 x 10^-12

r = [(1.67 x 10^-27)(2 x 10⁷)²] / 0.32 x 10^-12

   = 2.09 m

Physics Question of The Week (4)

A proton moves at a speed of 2 X 10⁷ m/s at right angles to a magnetic field with a magnitude of 0.10 T.  Find the radius of its circular orbit.  

Answer Key for Physics Question of The Week (3)

μ₀  =  ₄π x 10^-7  

I  =  5

r  =  30 cm =  .3 m

B  = 2 x 10^-5

B  =  (μ₀I) / (2πr)

(₄π x 10^-7)(5)  / (2π)(0.3)  =  (20 x 10^-7)  /  (0.6)  =  (10 x 10^-7)  /  (0.3)

(2 x 10^-5)(tan θ)  =  (10 x 10^-7)  /  (0.3) 

θ = 9.46⁰

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Physics question of the week (3)

A boat is sailing due north, as indicated by its compass needle, in a location where Earth's magnetic field is 2.0 X 10^-5 T. The boat’s captain inadvertently places his radio on the shelf directly above the compass.  If the 5.0 A current carrying wire of the radio is aligned in a north-south direction and is 30 cm directly above the compass, how much from due north with the compass needle be deflected?  

Answer Key for Math question of the week (4)

a.    d = 3

       u_n = a + n − d

       u₁₀₁ = 2 +100—3

       u₁₀₁ = 302 

b.   152 = 2 + (n −1)(3)

      150 = (n −1)(3),

      50 = n −1,

      152 = −1+ 3n

       n = 51