Month: February 2015

Charge is quantized. The elementary charge has the value:

e = 1.60×10^-19C

SP2. A penny, being electrically neutral, contains equal amounts of positive and negative charge. What is the magnitude of these equal charges?

M_penny = 3.1g

Atomic mass of copper = 63.546 amu

Atomic number of copper = 29

1 amu = 1.66×10^-24g

• Find number of Cu atoms in 3.1g
  • 3.1g / (63.546 amu * 1.66×10^-24g) = 2.94×10²²
• Find number of protons (or electrons)
  • 2.94×10²² x 29 = 8.522×10²³
• Find charge of protons (or electrons)
  • 522×10²³ * 1.60×10^-19C =136,358.9C

Answer is ~136,000C

Coulomb’s law describes the electrostatic force acting between the charges of two particles.

• F      = Force (Newtons)
• q1   = Charge of first particle (Coulombs)
• q2   = Charge of second particle (Coulombs)
• r²     = Distance between particles (Meters)