Physics MCQs
Topic Notes: Physics
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
11
Calculate the elastic potential energy stored in a 4m steel wire (cross-sectional area 3×10^-6 m^2) extended by 1mm, given Young's modulus is 2×10^11 Nm^-2.
Answer:
0.75
The elastic potential energy U is given by U = 1/2 * (Y * A * ΔL^2) / L. Substituting the values: Y = 2×10^11, A = 3×10^-6, ΔL = 1×10^-3, and L = 4. Calculation: U = 0.5 * (2×10^11 * 3×10^-6 * (1×10^-3)^2) / 4 = 0.5 * (6×10^5 * 1×10^-6) / 4 = 0.5 * 0.6 / 4 = 0.075 J. Note: The provided answer 0.75 may be a decimal error in the source.
12
What physical quantity is defined as the mass per unit volume of a substance?
Answer:
density
Density is a fundamental physical property defined as the ratio of an object's mass to its volume (ρ = m/V). It measures how compactly the matter is packed within a given space. It is an intensive property, meaning it does not depend on the amount of the substance present, and it is commonly measured in kg/m³ in the SI system.
13
Calculate the density of a wooden cube with dimensions 40 cm by 10 cm by 5 cm and a mass of 850 g.
Answer:
425 kgm-3
Density is mass divided by volume. The volume is 40 cm * 10 cm * 5 cm = 2000 cm³. Converting mass to kg (0.85 kg) and volume to m³ (0.002 m³), the density is 0.85 / 0.002 = 425 kg/m³. This calculation confirms the material's density relative to standard units.
14
Which physical property remains constant regardless of the amount of substance present?
Answer:
Density
Density is an intensive property of matter, meaning it does not depend on the size or amount of the sample. It is defined as the ratio of mass to volume (ρ = m/V). While mass and volume are extensive properties that change proportionally with the amount of substance, their ratio remains constant for a homogeneous material at a given temperature and pressure.
15
What is the dimensional formula for the elastic modulus (Young's, Bulk, or Shear modulus)?
Answer:
ML-1T-2
Elastic modulus is defined as the ratio of stress to strain. Since strain is a dimensionless quantity, the dimensions of elastic modulus are identical to those of stress. Stress is defined as force per unit area (Force/Area). Force has dimensions MLT^-2 and Area has dimensions L^2. Thus, (MLT^-2) / (L^2) results in ML^-1T^-2.
16
What is the defined ratio of tensile stress to tensile strain within the elastic limit of a material?
Answer:
Young’s modulus
Young's modulus, also known as the elastic modulus, is a mechanical property that measures the stiffness of a solid material. It is defined as the ratio of tensile stress to tensile strain in the linear elastic region of the material's stress-strain curve.
17
Match the types of strain and elastic moduli with their definitions.
Answer:
a-2, b-3, c-1, d-4
Linear strain involves a change in length (2). Volumetric strain involves a change in volume (3). Shearing strain involves a change in shape without changing volume (1). Young's modulus is defined as the ratio of normal stress to longitudinal strain (4). Thus, the correct mapping is a-2, b-3, c-1, d-4.
18
What is the modulus of rigidity for a liquid?
Answer:
zero
The modulus of rigidity (or shear modulus) measures a material's resistance to shearing forces. Liquids are fluids that cannot sustain a shear stress; they flow when subjected to such forces. Because a liquid cannot maintain a shape change under shear, its resistance to shear is zero, meaning the modulus of rigidity is zero.
19
Under what conditions is longitudinal strain typically described in material mechanics?
Answer:
under a large force change in length is smaller
Longitudinal strain is the ratio of the change in length to the original length. While the provided answer suggests a large force results in a smaller change in length, this is often context-dependent, such as in materials with high Young's modulus where significant force is required to produce even a small deformation.
20
What is the typical value for the Young's modulus of rubber?
Answer:
5×106 Nm-2
Young's modulus represents the ratio of tensile stress to tensile strain for a material. Rubber is a highly elastic polymer with a relatively low Young's modulus compared to metals, typically falling in the range of 10^6 to 10^7 Nm^-2 depending on the vulcanization and composition. The value 5×10^6 Nm^-2 is a standard representative value for common rubber materials.