NEET Physics: thermal expansion Practice Questions

Correct answer: B — Coefficient of Expansion

The amount of thermal expansion experienced by a substance is directly proportional to its coefficient of linear expansion (α).

Correct answer: C — The kinetic energy of the molecules increases

As temperature increases, the average kinetic energy of the molecules increases, causing them to move faster and occupy a larger volume.

Correct answer: D — The volume must increase.

Since density (ρ= m/V) is constant (assuming constant mass), if density remains constant, the volume must also remain constant. However, in thermal expansion context, if we consider thermal expansion, the statement implies a condition where the mass is constant. If we consider thermal expansion causing volume change while mass is constant, the density changes. The question implies a conceptual trap: if we are only considering volume changes due to heat, and we assume mass remains constant during the expansion process, this leads to a contradiction if density is strictly defined. For an ideal conceptual check: if ρ is constant, V must be constant. Since the question asks what must be true if density is *considered* constant, the implication is that the relationship is maintained, hence the volume doesn't change relative to mass changes. (Revisiting the core concept: If ρ is constant, V must change proportionally to m, which is complex. The simplest interpretation for an easy question is that for constant density, the volume remains fixed relative to that density constraint.) Let's rephrase for clarity: If the system is thermally expanded, density changes. If we force the condition that density is constant, volume is constant.

Correct answer: B — They decrease slightly

As temperature increases, the kinetic energy of the particles increases, causing them to move faster and push further apart. This increased spacing leads to a slight decrease in the net intermolecular forces holding the substance together, resulting in expansion.

Correct answer: B — Decrease

Since thermal expansion increases the volume while the mass remains constant, the density (ρ= m/V) must decrease.

Correct answer: D — Gases expand significantly upon heating

Gases expand significantly upon heating because the increased thermal energy allows the molecules to move farther apart, increasing the volume.

Correct answer: A — Length and Volume

Thermal expansion results from the change in the dimensions (length and volume) of the substance due to the increase in kinetic energy of the molecules.

Correct answer: C — γ= 3α

For solids, the coefficient of volume expansion (γ) is three times the coefficient of linear expansion (α). Thus, γ= 3α.

Correct answer: B — 0.1 K⁻¹

For area expansion, ΔA/A = βΔT, where β= 2α. If ΔA/A = 0.10, then 2αΔT = 0.10. Assuming ΔT = 1 K (for conceptual simplicity in this context), 2α≈ 0.10, so α≈ 0.05 K⁻¹. (Revising the options/context for simplicity based on easy recall: If expansion is 10%, α is half of the corresponding volume expansion factor, making 0.05 the most reasonable conceptual answer among the choices, assuming standard unit definitions).

Correct answer: D — Thermal expansion

The increase in the volume occupied by the material due to the increase in the kinetic energy of its constituent particles upon heating is known as thermal expansion.

Correct answer: A — The original length and the coefficient of linear expansion

The change in length (ΔL) is given by ΔL = L₀ αΔT, showing that expansion is directly proportional to the original length and the coefficient of linear expansion.

Correct answer: C — ΔV = VαT

The formula for volume expansion is ΔV = VαΔT, where ΔT is the change in temperature.

Correct answer: D — Specific Heat Capacity

While γ is fundamentally linked to α, the material's response to thermal change (and thus γ) is heavily influenced by its specific heat capacity (C) and its elastic properties, which determine how energy is distributed.

Correct answer: B — Coefficient of Volume Expansion

The increase in volume (ΔV) of a solid upon heating is quantified by its coefficient of volume expansion (γ). While density (ρ) changes, the expansion itself is directly governed by the coefficient of volume expansion, which relates the fractional change in volume to the change in temperature and the original volume (ΔV = γV₀ ΔT).

Correct answer: A — Volume and Length

Thermal expansion primarily manifests as a change in the dimensions (length, area, and volume) of a material when its temperature changes.