Physics Quiz on Density and Measurements

Gold Sheet Thickness Calculation

• 1.00 oz of gold has a mass of 28.350 g.
• Gold's density is 19.3 g/mL, allowing conversion of mass to volume.
• Volume of gold = mass/density = 28.350 g / 19.3 g/mL = 1.47 mL.
• If the volume covers an area, thickness can be calculated using thickness = volume/area.

Significant Figures in Calculations

• Significant figures represent the precision of a measurement.
• In the expression (1.4312 - 1.1 × 10^-2) ÷ (1.0712 × 10^-4), the calculation's significant figures depend on the least precise measurement.
• Subtraction dictates the number of decimal places; division dictates the total significant figures.

Temperature Conversion

• Core temperature of the warp drive is approximately 3 million degrees Celsius.
• Use the formula: °F = (°C × 9/5) + 32 to convert to Fahrenheit.
• Converted value is significant for discussions of technology and science fiction.

Neutron Count in Atoms

• Atoms can differ in neutron count, affecting stability and isotopic abundance.
• Identifying the atom with the greatest neutron count requires reviewing periodic table data.

Atomic Mass of Sulfur

• The mass of a single sulfur atom can be calculated using Avogadro's number (6.022 × 10^23) and the molar mass of sulfur (approximately 32.07 g/mol).

Calcium Abundance in Earth's Crust

• The natural abundance of calcium is 3.4% by mass in the crust.
• To find the number of calcium atoms in a 1.50 g sample, use the formula: (mass of sample × abundance) / (molar mass of calcium).

Cation Symbols

• A cation with 13 neutrons and 10 electrons that carries a +1 charge suggests an atomic number of 11 (sodium).
• The correct ion symbol would be Na+.

Isotopic Mass of Magnesium

• Isotopes of magnesium include 24Mg, 25Mg, and 26Mg; their weighted contributions determine the average atomic mass.
• Calculating the atomic mass of 26Mg requires information about its isotopic mass and natural abundance distribution.

Bohr Theory and Emission Spectra

• Emission spectra relate to electron transitions between energy levels.
• The Bohr theory articulates how energy released during these transitions produces specific spectral lines.

Wavelength of a Truck as Matter Wave

• Associated wavelength can be calculated using the de Broglie equation: λ = h/mv, where h is Planck's constant, m is mass, and v is velocity.
• The result reveals quantum characteristics of large objects like trucks.

Uncertainty in Electron Position

• Position uncertainty relates to the speed of an electron and the uncertainty in speed.
• Use the Heisenberg uncertainty principle to relate position and velocity uncertainties.

Molar Mass of Unknown Compound

• Given 1.00 g containing 8.35 × 10^21 molecules, molar mass can be calculated by dividing total mass by the number of moles (using Avogadro's number).

Moles and Atoms of Gold in 14K Gold

• 14K gold is 58% gold by weight.
• Volume of a cube can be calculated; then, using density and percentage composition, find moles and atoms of gold in the sample.
• Use density of 14K gold (14.0 g/mL) for calculations.