CBSE Class 12 Physics Solids and Fluids Objective Questions

CBSE Class 12 Physics Solids and Fluids Objective Questions. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

1. Two bars A and B of circular cross-section and of same volume and made of the same material are subjected to tension. If the diameter of A is half that of B and if the force applied to both the bars is same and it is within elastic limits, the ratio of extension of A to that of B is
(a) 2 (b) 4 (c) 8 (d) 16s

2. An iron rod of Y = 10¹¹ N / m² and coefficient of linear expansion 10^–5 / 0C has a length of one metre and area of cross-section 10 cm². If its temperature is raised by 1000C and it is held so that it is not allowed to expand or bend, the force produced is
(a) 10³ N (b) 10⁴ N (c) 10⁵ N (d) 10⁶ N

3. A thick cylindrical metallic rod of density ρ, Young’s modulus Y and length L is suspended from a rigid support. The increase in length of the rod due to its own weight is
(a) ρ g L/Y (b) ρ gL²/Y (c) ρg L²/ 2Y (d) ρg L²/4Y

4. A 20 Newton block is suspended from a wire such that its length changes by 1 %. If Young’s modulus of material of the wire is 2 × 10¹¹ Nm^–2, the area of cross-section of the wire is
(a) 1 mm² (b) 10^–1 mm² (c) 10–2 mm² (d) 10^–3 mm²

5. A metallic rod breaks when the strain produced is 0.2 %. Young’s modulus of the material of the rod is 7 × 109 N / m. The area of cross-section to support a load of 104 N is
(a) 7.1 × 10^–2 m² (b) 7.1 × 10^–4 m² (c) 7.1 × 10^–6 m² (d) 7.1 × 10^–8 m²

6. Bulk modulus of rubber is 9 × 108 N / m2. The depth below the surface of sea where a solid rubber ball should be taken to reduce its volume by 0.1 % is (Given that atmospheric pressure at sea level is equal to 10 m of column of water)
(a) 10³ m (b) 10² m (c) 10 m (d) 1 m

7. A solid sphere of radius R made of a material of bulk modulus K is surrounded by a liquid in a cylindrical container. A massless piston of area A floats on the surface of the liquid when a mass M is placed on the piston to compress the liquid. The fractional change in the radius of the sphere is
(a)  mg/ 4KA (b)  mg/ 3KA (c) 3KA/ mg  (d)  4KA/mg 

8. Young’s modulus of steel and brass are 2 × 10¹⁰ N/m² and 10¹⁰ N/m² respectively. A steel and brass wire of the same length are extended by 1 mm under the same force, the radii of steel and brass wires are R_s and R_B respectively. Then
(a) R_S = √2 R_B (b) Rs=R_B /√2 (c) R_S = 4R_B (d) Rs= R_B/4

9. Two capillary tubes of same radius r but of lengths l1 and l2 are fitted in parallel to the bottom of vessel. The pressure head is P. What sould be the length l of the single tube that can replace the two tubes, so that the rate of flow is same as before.

(a) l = l₁ + l₂ (b) l =l₁l₂ /  l₁ + l₂ (c) l= 1/ l₁+1/l₂  (d) l=1/  l₁ + l₂

10. One end of a uniform wire of length L and of weight W is attached rigidly to a point in the roof and a weight W1 is suspended from its lower end. If S is the area of cross-section of the wire, the stress in the wire at height 3L/4  from its lower end is
(a) W₁/S  (b) (W₁  +W/4)S   (c) (W^₁  +W/4)/S (d) W^₁+ W/S 

11. A metal rod has Young’s modulus Y, length L and area of cross-section A. The work done in stretching
the rod by an amount ΔL is
(a) YA(ΔL)²/ 2L (b) YA(ΔL)²/ L (c)  YA(ΔL) /2 L (d) YA(ΔL)/L

12. The following four wires are made of the same material. Which of these will have the largest extension when the same tension is applied ?
(a) length 50 cm, diameter 0.5 mm (b) length 100 cm, diameter 1 mm
(c) length 200 cm, diameter 2 mm (d) length 300 cm, diameter 3 mm

13. A nylon rope 3 cm in diameter has a breaking strength of 1.5 × 10⁵ N. The breaking strength of a similar
rope 1.5 cm in diameter is
(a) 7.5 × 10⁴ N (b) 3.75 × 10⁴ N (c) 3 × 10⁵ N (d) 6 × 10⁵ N

14. A highly rigid cubical block A of small mass and side L is fixed rigidly on to another cubical box B of the same dimensions and of low modulus of rigidity η such that the lower face of A completely covers the upper face of B. The lower face of B is rigidly held on a horizontal surface. A small force F is applied perpendicular to one of the side face of A. After the force is withdrawn, block A executes small oscillations, the time period of which is given by
(a) 2π √Mη L (b) 2π √Mη/L (c)  2π √ML/η   (d)  2π √M/ηL

15. On end of a long metallic wire of length L is tied to the ceiling. The other end is tied to a massless spring of spring constant K. A mass m hangs freely from the free end of the spring. The area of cross-section and Young’s modulus of the wire are A and Y respectively. If the mass is slightly pulled down and released, it will oscillate with a time period T equal to
(a) 2π √ m/K(b) 2π √m(YA+KL)/YAK (c) 2π√mYA/KL (d) 2π√mL/YA

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