Chemists (and Astronomers!) like to express lengths in Angstrom units where 1 An

Question

Chemists (and Astronomers!) like to express lengths in Angstrom units where 1 Angstrom = 10^-10 m. roughly the length of a chemical bond What is the repulsive energy of two protons that are 1 Angstrom unit apart? State your answer in both joules and Electron Volts. The resistivity of carbon is 3.5x10^-5 ohm m. Remembering that R = rho L/A. how long a piece of carbon. 1 mm in radius would be needed for a 4000 ohm resistor. What would the electric field be inside the resistor if the two ends were kept at a 5 volt difference in potential? A 2000 ohm resistor and a 125 mu F capacitor are connected in series and the combination placed across the terminals of a 100 Volt battery. What is the current through the resistor a time 0? What will the current be at long times? What is the charge stored in the capacitor at time 0? What will the charge be at long times? What are the SI units of energy electric field capacitance Magnetic field Electric current Electric charge Elec

Explanation / Answer

C)   = 3.5*10^-5 ohm-m

      A = pi*r^2 = pi*10^-6 = 3.14*10^-6 m^2

      R = 4000 ohm

      Now   L = RA/ = (4000*3.14*10^-6)/3.5*10^-5 = 358.86 m

       Electric field = E = V/L = 5/358.86 = 0.01393 N/C

4) a) Current through resistor at t = 0 ===> I = V/R = 100/2000 = 0.05 A

b) Current after long time = I = 0.05 A

c) Charge stored in capacitor at time 0 ===> Q = 0

d) Charge after long time = Q = CV = 125*10^-6*100 = 0.0125 C

5) Energy =======> Joule(J)

Electric Field ====> V/m or   N/C

Capacitance =======> Farad (F)

Magnetic Field =======> Tesla (T)

Electric Current =======> Ampere (A)

Electric Charge =======> Coulomb (C)

Electric Current =======> Ampere (A)

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