Question

1. what caused the weight on the iron wire to move down when the wire heated up?

options: hot objects expand; hot objects weigh more; hot objects are more dense; hot objects get weaker

1. which defect is not a point defect?

options: dislocation; interstitial; substitutional; vacancy

1. which alloy is made by combining two elements with interstitial defects?

options: brass; bronze; nitinol; steel

Explanation:

Question 55

When an iron wire is heated, it expands (thermal expansion). This expansion makes the wire longer, so the weight attached moves down. Hot objects don't weigh more (mass/weight is conserved), aren't more dense (expansion increases volume, decreasing density), and "weaker" isn't the reason for the weight moving down here. So the correct reason is hot objects expand.

Point defects in crystals involve individual atoms/ions (vacancy, interstitial, substitutional). Dislocation is a line defect (involves a row of atoms), not a point defect. Interstitial (extra atom in interstice), substitutional (atom replaced), and vacancy (missing atom) are point defects.

Interstitial alloys form when small atoms fit into interstices of a metal lattice. Steel is an interstitial alloy (carbon atoms in iron's lattice). Brass (Cu - Zn) and bronze (Cu - Sn) are substitutional. Nitinol is a shape - memory alloy with different bonding, not interstitial in the same way as steel.

Answer:

A. hot objects expand

Question 56