PHYS 2422 PRACTICE EXAM #1 21 JANUARY 2017 NAME ___________________________

Work the following four problems in Chapter 21:

54) A charge 6.0 µC is to be spilt into two parts that are then separated by 3.0mm. What is the maximum possible magnitude of the electrostatic force between those two parts?

54) Use Coulomb’s law which states that 𝐹 = 𝑞1𝑞2

4𝜋𝜀0𝑟2 =

𝑞1(𝑄−𝑞2)

4𝜋𝜀0𝑟2

59) What is the total charge in coulombs of 75.0 kg of electrons?

59) n = M/m, q = -ne

69) In the radioactive decay of Eq. 21-13, a 238U nucleus transforms to 234Th an ejected 4He. (These are nuclei, not atoms, so no electrons are involved.) When the separation between 234Th and 4He is 9.0 X 10-15m, what is the magnitude of (a) the electrostatic force between them and (b) the acceleration of the 4He particle?

69) First, Coulomb’s law 𝐹 = 𝑘𝑒2

𝑟2 , 𝑎𝑛𝑑 𝐹 = 𝑚𝑎. k = 8.99 X 109Nm2/kg2, mn = 1.67 X 10-27kg. 234Th has 90

protons and 4He has two protons and two neutrons. Assume all nucleons have the same mass.

74) A 100W lamp has a steady current of 0.83A in its filament. How long is required for 1 mol of electrons to pass through the lamp?

74) 𝑖 =∆𝑞

∆𝑡, 𝑤ℎ𝑒𝑟𝑒 ∆𝑞 = 𝑁𝐴𝑒, 𝑢𝑠𝑖𝑛𝑔 𝑁𝐴 = 6.022 𝑋 1023, 𝑎𝑛𝑑 𝑒 = 1.602 𝑋 10−19𝐶

Work the following four problems in Chapter 22:

62) (a) What is the magnitude of an electron’s acceleration in a uniform electric field of magnitude 1.40 X 106 N/C? (b) How long would the electron take, starting from rest, to attain one-tenth the speed of light? (c) How far would it travel in that time?

62) (a)𝑎 =|𝑞|𝑒

𝑚 (b) C = C/10, t = 𝑡 =

∆𝑣

𝑎 (c) ∆𝑥 =

𝑣2−𝑣02

2𝑎

71) A charge of 20 nC is uniformly distributed along a straight rod of length 4.0 m that is bent into a circular arc with a radius of 2.0 m. What is the magnitude of the electric field at the center of curvature of the arc?

71) |�⃑� | = ∫𝜆

4𝜋𝜀0𝑟

𝜃

−𝜃𝑠𝑖𝑛𝜃𝑑𝜃

76) In Fig. 22-67, an electric dipole swings from an initial orientation i ( = 110.0 degrees) to a final

orientation of f (f = 70.0 degrees) in a uniform external electric field E. The electric dipole moment is 1.60 X 10-27 C*m; the field magnitude is 3.00 X 106 N/C. What is the change in the dipole’s potential energy?

76) 𝑈 = −𝑝𝐸𝑐𝑜𝑠Δ𝜃.

80) Calculate the electric dipole moment of an electron and a proton 4.30 nm apart.

80) p=qd.